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ABSTRACT

EFFECTS OF METHYL SUBSTITUTION ON THE PHOTOPROCESSES
OF ALKYL PHENYL KETONES

BY

Eugene George Harris

Photochemical studies were conducted to determine the
effects of methyl substituents on the rates of hydrogen
abstraction (kr) and radiationless decay (kd) from the
triplet states of butyro and valerophenone. Methyl groups
were added in the series: EEEE methyl, REES methyl,
3,4-dimethyl, and 3,5-dimethyl. Values for kr and kd were
calculated from solvent studies and Stern Volmer quenching
plots.

The rates of radiationless decay were found to be
larger for the ESEE substituted phenyl ketones. The 3,4-
dimethyl ketones possessed kd values which were determined
to be about the same as those for the paaa substituted
ketones. The 3,5-dimethy1 ketones possessed kd values that
were lower than those of the maaa methyl ketones.

The faster rates of hydrogen abstraction for the EEEE
substituted ketones were proposed to be the result of the

larger (n,n*)-(n,n*) triplet separations in the para isomers.

Eugene George Harris

An additivity relationship was noted for the relative rates
of hydrogen abstraction among the various isomers of the
methylated ketones. These rates showed a reasonable
correlation to (n,n*)-(n,n*) triplet separations which had

been determined from earlier phosphorescent excitation

studies.

EFFECTS OF METHYL SUBSTITUTION ON THE PHOTOPROCESSES
OF ALKYL PHENYL KETONES

By

Eugene George Harris

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Chemistry

1973

To Paula
for her endurance and

understanding

ii

ACKNOWLEDGMENTS

Appreciation is gratefully extended to Professor
Peter J. Wagner for his guidance and support during the

author's term of study.
The author also acknowledges the financial support

from Michigan State University and the National Science

Foundation.

iii

TABLE OF CONTENTS

INTRODUCTION. . . . . . . . . . . . . . . . .

A.

RESULTS
A.

B
C.
D

Substituent Effects on the Photoreduction
of Ketones . . . . . . . . . . . . .

1) Review of Photoreduction .
2) Substituent Effects - Meta and Para.

3) Ortho Substituent Effects.

Substituent Effects on the Type II Reaction.

1) Review of the Type II Reaction .

2) Effects of Ring Substituents on the
Type II Photoreaction. . .

Objectives

Kinetics of Experimental Techniques. .

1) Representation of the Type II Process.
2) Energy Transfer.

3) Determination of Reactivity.

4) Effect of Revertible Hydrogen Transfer
Absolute Type II Quantum Yields.
Cyclobutanol Quantum Yields.

Stern Volmer Quenching Slopes.

Solvent Studies.

iv

Page

t9 ha rd

U1

10
11
11
14
15
16
18
18
18
19
20

TABLE OF CONTENTS (Continued)

E. Dependence of Quantum Yields on Ketone
Concentration.
F. Disappearance Quantum Yields
G. UV Absorption of Methylated Butyrophenones
DISCUSSION.
A. Effects of Methyl Substitution on
Reactivities and Radiationless Decay of
Triplet State.
B. Additivity of Substituents Effects
C. The High Rate of Radiationless Decay of
Valerophenones . . . . . . . . .
D. Summation.
E. Further Studies.
EXPERIMENTAL.
A. Chemical

1) Dependence on Purity
2) Preparation of Ketones
a) Method I
b) Method II. . . . . . . . . .
c) Method II-a.
3) Photolysis Products.
a) Acetophenone
b) .Maaa-Methylacetophenone.

c) Para-Methylacetophenone.

Page

20
21
21
32

32
39

41
42
42
44
44
44
44
44
45
46
46
46
46
46

4)

5)

6)

TABLE OF CONTENTS (Continued)

d) 3,4-Dimethy1acetophenone
Solvents

a) Benzene.

b) t-Butyl alcohol.
c) Heptane.

d) Pentane.

e) Pyridine

f) Ethanol.
Internal Standards
a) Tetradecane.

b) Pentadecane.

c) Hexadecane .

Quenchers.

a) cis-l,3-Pentadiene (piperylene).

b) 2,S-Dimethyl-2,4-hexadiene

Methods of Analysis.

1)

2)
3)
4)

Preparing Ketones for Photolysis
a) Making Solutions

b) Degassing.

Photolysis

Analysis of Photolyzed Solutions

Product Identification .

vi

Page
46
46
46
49
49
49
49
49
49
49
50
50
50
50
50
50
50
SO
SO
SO
52
53

5)
6)
7)

8)
KINETIC DATA.
BIBLIOGRAPHY.

TABLE OF CONTENTS (Continued)
Standardization Factors.
Actinometry.

Ketone Disappearance and Cyclobutanol
Yields . . . . . . . . . . . . .

Reliability of Data.

vii

Page
55
55

S6
57

58
76

TABLE

10

11
12
13
14
15

16

LIST OF TABLES

Photokinetic Parameters.

Data for Solvent Studies .
Substituent Effect on the S + 1La
Transitions of Acylbenzenes. . . . .

Substituent Effects on Triplet State
Reactivities of Butyrophenone.

Substituent Effects on Triplet State
Reactivities of Valerophenone.

Phosphorescent Excitation O-O Bands of
Several Methylated Acetophenones

Additivity of Substituent Effects on
Reactivities . . . . . . . . . . .

Additivity of Substituent Effects in
Spectroscopic Data . .

Physical Data for Synthesized Ketones.

Stern-Volmer Quenching of .l M para-Methyl-

butyrophenone by 2,S-Dimethyl-Z,4-hexadiene.

Photolysis of meta-Methylbutyrophenone
Photolysis of 3,4-Dimethy1butyrophenone.

Photolysis of 3,S-Dimethylbutyrophenone.

Photolysis of .l M Para-methylvalerophenone.

Photolysis of .l M 3,5-Dimethy1-
valerophenone. . . . . . . . . .

Photolysis of .1 M 3,4-Dimethyl-
valerophenone. . . . . . . . . .

viii

Page
22
23

24

34

35

36

39

41
47

59
60
61
62
63

64

65

TABLE
17
18
19

20
21
22
23
24
25
26
27
28
29
3O
31
32

Solvent Study

Photolysis

Photolysis

buterphenone.

Photolysis
Photolysis
Photolysis
Photolysis
Photolysis
Photolysis
Photolysis
Photolysis
Photolysis

Photolysis

of
of

of
of
of
of
of
of
of
of
of
of

LIST OF TABLES (Continued)

of a para-Methylbutyrophenone.

meta-Methylbutyrophenone

.1 M 3,4-Dimethy1-

3,S-Dimethylbuterphenone.
aaaa-Methylvalerophenone
3,4-DMVP .

3,5-DMVP .
p-Methylbutyrophenone.
3,4-Dimethy1butyrophenone.
3,S-Dimethylbutyrophenone.
m-Methylvalerophenone.
3,S-DimethylvalerOphenone.

3,4-Dimethy1va1erophenone.

Data for Cyclobutanol Ratios

Standard-Product Molar Response Ratios

Experimental Data for Determining
Disappearance Quantum Yields

ix

Page
66
67

68
69
69
70
7O
71
71
72
72
72
73
73
74

74

FIGURE
1

10

11

12

LIST OF FIGURES

Electron density in 3(n,1r*) and 3(11,")
states . . . . . . . . . . . .

Jablonski diagram of the photolysis of
valerophenone with a quencher present.

Photolysis of valerophenone.
Dependence of kq on low viscosity solvents

Relationship of type II quantum yield to
ketone concentration 0 p- methylbutyrophenone,
D 3, 4- dimethylbutyrophenone, A3, 5- dimethyl-
butyrophenone. . . . .

Relationship of type II quantum yield to
ketone concentration; 0 m- methylvalero-
phenone, E13, 5- dimethylvalerophenone,

3, 4- -dimethylvalerophenone. .

Stern Volmer quenching plots for 0 3,4-
dimethylbutyrophenone, Cl3,S-dimethyl-
butyrophenone. . . . . . . . . . .

Stern Volmer quenching plot for
p-methylbutyrophenone.

Stern Volmer quenching plot for 3, 4-
dimethylvalerophenone. . . .

Stern Volmer quenching plot for meta-
methylbutyrophenone.

Stern Volmer quenchin plots for 0 para-
methylvalerophenone, 3,5-dimethy1-
valerophenone. . . . . . . . .

Relationship of type II quantum yield to
added amounts of t- butyl alcohol in benzene.
0 meta- methylvalerophenone, A 3, 4- dimethyl-
valerophenone, E13, 4- dimethylvalerophenone,
O 3,4-dimethy1butyrophenone. . . .

Page

12
13
14

25

25

26

27

28

28

29

3O

FIGURE
13

14
15

16

LIST OF FIGURES

Effect of pyridine on type II reaction in
benzene. Q meta- methylbutyrophenone,

Apara- methylbutyrophenone, ”D 3, 5- -dimethyl-

butyrophenone.
VPC trace of 3,4-dimethy1valerophenone

Absorbtion spectra for a)m -methylbutyro-
phenone, b) p- methylbutyrophenone. .

Absorbtion spectra for a) 3,4-dimethy1-

butyrophenone, b) 3,S-dimethylbutyrophenone.

xi

Page

31
54

75

75

INTRODUCTION

The photochemistry of ketones has undergone extensive

1-6 As a result the mechanisms

examination in recent years.
for many photoprocesses are becoming fairly well understood.
However, no general understanding of the steric and
electronic effects of ring substituents on the photochemistry
of phenyl ketones yet exists. The following study of the
type II process of maEa-and Raga-methylated phenyl ketones

was initiated to clarify some of these electronic effects.

A. Substituent Effects on the Photoreduction of Ketones

1) Review of Photoreduction

The first experimental evidence of photoreduction came
when Ciamician and Silber identified the pinacol and
corresponding aldehyde or ketone from benzophenone irradiated

7

in alcohols. Acetone and acetophenone were also found to

photoreduce.7’8

Numerous hydrogen donor solvents have been
employed in the photoreduction process.8 Hirshberg
completed the first systematic studies in the late thirties.
He proposed the first step of photoreduction to be a

diradical formation, (Equation 1).

 

I 2* CH
\ n 3
© W3 h" >

Hammond later found, as did Hirshberg, that optically
active alcohols did not racemize and so concluded that
disproportionation and reversal of the abstraction process

10

did not take place (Equation 2). Quenching studies of

H 'H on

i" 9
. c . /£
(C?) E + CH3/*'1\CH3 E G G I CH3 \CH5 ——> Products

(2)

benzophenone with O2 and olefins indicated that the reacting
species was a triplet.11
2) Substituent Effects - Maaa and Paga
The first substituent effects were noted by Bergman

and Hirshberg in 1943.12

They found that only a limited
number of ketones were susceptible to photoreduction

(Equation 3).

hv
RCOR' + c113c11011c113 ———> RR'COHCOHRR' + CHSCOCH3 (3)

Acetyl naphthalenes, a naphthyl phenyl ketones, and di-a-
naphthyl ketones did not undergo photoreduction. They found

that meta-phenylbenzophenone forms a small amount of pinacol

whereas the 221$ and QEEEQ isomers do not. Methoxy-
substituted acetophenones also do not react. The low
reductivity for this group of ketones involves the nature
of the lowest triplet state, with the 3(n,1r*) state being

generally reactive and the 3(n,1r*) state nonreactive

13

toward hydrogen abstraction. The 3(n,1r*) state resembles

an alkoxy radical in its reactivity and so possesses the

greater electrOphilicity (Figure l).14’15

.5.“ -‘o'- ..
¢\C *6 ¢\C—-O . '; U\R ‘3.
=.. H ' ..‘ - R \R
R/ R/ Q” <- 6? -- <3”
3(n,w*) 3(n.n*)

Figure 1. Electron density in 3(n,1r*) and 3(n,n) states.

Phosphorescence studies have shown that ketones such as

para-phenyl and para—aminobenzophenone have low lying

16,17

3(1r,1r*) states. Pitts and workers photolyzed various

p-aminobenzophenones and found little photoreduction by

alcohols.18

Higher yields were noted, however, for para-
methoxy and -phenyl substituents.19 Porter and Suppan
studied, in some detail, the relationship between the

spectroscopic and photochemical properties of substituted

benzophenones.20

Amino, dimethylamino, or hydroxy groups
substituted into the ring at the EEEE or EEEE positions
reduce the photoreduction quantum yield in alcohol to near
zero. The pinacol yield increases in paraffins for the
p-amino but not for maaa-aminobenzophenone. This fact has
been attributed to an inversion for the 3(n,1r*) and 3(1r,1r*)
states in the 2212 isomer which can be deduced from
spectroscopic data. Pinacol formation for the methoxy
derivative was found to be 10 times that of the hydroxy,
even though their spectra are nearly identical. A lowest

charge transfer triplet, 3

CT*, was invoked to explain the
large difference in reactivities, with deprotonation of the

hydroxyl occurring in the excited state (Equation 4).

:O:(_)

”OOQJH @©H°©©

The intermediate reactivity of phenyl-substituted benzo-
phenone was attributed to its lowest triplet being a
3(1r,1r*). Paaa and EEEE methyl substituents on benzophenone
produce only a small reduction in quantum yield of pinacol
formation while a Raga-trifluoromethyl group slightly

21

increase the pinacol yield. Mixing of the lower 3(n,n*)

state with the upper 3(w,n*) state was said to be the origin

of the former effect. The increase in pinacol formation
in the latter case was rationalized as an inductive effect.
Yang demonstrated, however, that methylation of aceto-
phenone produces a lowest 3(n,fl*) which still photoreduces
with considerable quantum efficiency in 2-propanol.22’23
It was suggested that the reduction efficiency depends on
the extent of vibronic coupling between the 3(n,1r*) and

3(fl,fl*) states.23

The methylated acetophenones have a
considerably slower rate of non radiative decay than does
acetophenone, which has a lowest 3(n,1r*) state. Maaa methyl
and methoxy substituents lower pinacol quantum yields more
than the EEEE isomers do and also produce longer radiative
lifetimes.

3) Ortho Substituent Effects

Yang, in 1961, provided evidence for the photo-
enolization (Equation 5) of a-methylbenzophenone, which
had been proposed as the reason for the low photoreduction

24

yields from ortho-alkyl phenyl ketones. The following

3 OH
=0 —-—>h" d; / (5)
l 6 A C\R

year Yang demonstrated that the precusor of the photoenol

25

was a triplet rather than a singlet. The dependency of

the rate of photoenolization on structure has been

26

established. Photoenolization has also been reported as

the pathway for the reduction of triplet activity for

EEEEE‘hydroxy phenyl ketones (Equation 6).18'19’20’27

O
/O / hv 9 d: /OH (6)
\R ‘ A \R

B. Substituent Effects on the Type II Reaction

OH

 

1) Review of the Type 11 Reaction
Phenyl alkyl and dialkyl ketones containing gamma
C-H bonds undergo, upon irradiation, 1,5 hydrogen shifts

to yield cleavage and cyclization products (Equation 7).

/o 6
CW II —>*” CW
\CHZ-CH ' A

2 CH -CH

 

V

 

:22-
v
// \
a a
Na
:2

//

 

+ CH =CH2 (7)

The cleavage reaction with ketones is commonly called

28

Norrish type II photoelimination. The cyclization

reaction to form cyclobutanols was first discovered by

Yang in 1958.29

Both of these reactions involve the
transfer of hydrogen from the y carbon to the carbonyl
oxygen. In the photoelimination reaction, ketone formation
has been shown to proceed via the enol.30’31 Although
dialkyl ketones react from both singlet and triplet, in the
phenyl alkyl ketone system, where intersystem crossing from
the singlet to triplet is extremely rapid, both elimination

32-37 A

and cyclization occur only from the triplet.
1,4-biradical intermediate has been demonstrated, with
little doubt, to intervene in triplet state type 11

reactions.38

The fact that this intermediate can undergo
reversal of the hydrogen abstraction process, as well as
product formation, was not taken into account by early
research groups who tried to compare quantum yields to

13,39,40

triplet reactivity. Wagner has shown that added

hydrogen bonding solvents maximize quantum yields by

41 Reactivities

eliminating the reverse hydrogen transfer.
of the triplet may be obtained from Stern Volmer plots, of
which more will be said later.
2) Effects of Ring Substituents on the Type II
Photoreaction

The use of the Type II reaction to ascertain structure-

reactivity relationships in ring substituted ketones was

thought to be preferable to analogous studies using inter-
molecular photoreduction, mainly because of the control

of C-H bond strength during drastic solvent changes.
Pitts, in 1966, found substituent effects on the quantum
yield of buterphenone reaction similar to those observed

for benzophenones.13

The photoelimination quantum yield

for p-hydroxy, p-amino, and p-phenyl were negligible and

the phosphorescent lifetimes were long, ~.08 sec. The
lifetimes for p-methyl, p-fluoro, and p-acetoxybutyrophenones
were shorter, ~.004 sec, and displayed higher quantum yields.
Pitts considered the latter ketones to possess 3(n,1r*)

lowest triplets. p-Methoxybutyrophenone had an intermediate
lifetime and quantum yield. In a later communication Pitts
found the aaaa substituted methoxy and acetoxy butyro-
phenones to have a quantum yield, in benzene, one tenth

that of the QEEEQ and 223% substituted ketones and a

phosphorescent lifetime a factor of 10 longer.:59

The aa£a_
substituents were thought to lead to 3(n,n*) lowest triplets
while the agaaa and EEEE substituted methoxy and acetoxy
butyrophenones were not classified. The m,p-fluoro, methyl
and chloro all behaved similarly and were held to have a
3(n,1r*) lowest triplet. Pitts suggested that the energy
separation of the 3(n,1r*) and 3(1r,1r*) triplets might be
rather small in certain solvents, as dual phosphorescent

emmission had been observed for similar ketones.4o’42’43

The most in depth work on the type II reaction has been

completed by Kemppainen on the substituted valerophenone

system.43 Quenching studies in combination with spectro-

scopic data have somewhat clarified the effect of
substituents on the photoelimination quantum yields and

44’1 There are two effects which determine

reactivities.
quantum yields in type 11 reactions. The first is an
inductive effect on the disproportionation of the biradical
and the second is the lowering of the reactivity of the
triplet through inversion of the 3(n,1r*) and 3(1r,1r*)

45

triplets. The former effect is present with groups

such as p-trifluoromethyl or a pyridyl ketone.1’46
Addition of alcohol promotes a ¢II of unity which indicates
that these lowest 3(n,1r*) triplet ketones have negligible
direct decay from their triplets. The increase in
reactivity for the strongly electron withdrawing groups
seems to be an inductive effect on the already electro-

21,47

philic triplet. Since the 3(1r,1r*) lies only a few

kcal above the 3(n,n*) in phenyl alkyl ketones, electron
donating substituents or a highly polar solvent can invert

the ordering of the states.43’48’49

As well as having longer
lifetimes, the type II quantum values for the chloro, methyl,
and methoxy substituted alkyl phenyl ketones do not reach
unity upon addition of increments of alcohol. Such

behavior indicates some type of direct triplet decay

41,49

competitive with y-hydrogen abstraction. Quenching

10

studies also show that the ketones with lowest 3(1r,1r*)
triplets show marked reduction in rates of hydrogen

50

abstraction. Yang and Dusenberg, in their work with

methylated acetophenones, also demonstrated reduced kr

values for these lowest 3(fl,n*) triplets.23

Wagner has
shown that a reactive upper 3(n,1r*) state in equilibrium
with a lower unreactive 3(1r,1r*) state best explains the

experimental data.51

Since spectroscopists have indicated
that the triplets are vibronically mixed, some reactivity

from the lowest 3(1r,1r)* state is not ruled out for ketones
where the states are close (<2 kcal

40,43,47,48,52,53

separation). Chloro and methyl substituted

44 It was also

phenyl ketones would fall in this category.
noted that maaa-methyl and methoxy substitution produced
shorter lifetimes and lower quantum yields. These
observations point to a higher radiationless decay for

these meta substituted ketones.

C. Objectives

The difference in the kd values for the ESEE and EEEE
isomers poses an interesting question. Quenching by ground
state ketone might possibly be an answer. This would be
supported by an increase in type II yield with a concurrent
decrease in ketone concentration. Perhaps the difference
reflects vibronic effects leading to radiationless decay.

The work described in this thesis was begun on the

11

proposition that varying the quantity and position of
methyl groups in the phenyl ring of alkyl phenyl ketones
might yield information on the excited triplet's
electronic structure. As the number of methyl groups
increase and their positions vary, one would expect a
transition from the small effect of one methyl group to

the large effect of one methoxy group.

D. Kinetics of Experimental Techniques

1) Representation of the Type 11 Process

Figure 2 is a modified Jablonski diagram which gives
a pictorial view of the excitation to and possible modes
of decay from the two lowest electronic states of valero-
phenone. A schematic of the photolysis of valerophenone

is given in Figure 3.

 

12

 

 

 

 

 

1C
(“‘31:“)
3
'———-__-== Tr , 7‘
k.
1C

3

__+___ n,n
kr

Biradical
kic Internal conversion; Intersystem crossing;

kq[Q] Quenching by an energy Cacceptor;
kr Hydrogen abstraction; k-r Reversal of hydrogen

abstraction (to ground state);
kd Radiationless decay to ground state;
Wavy lines represent vibrational decay.

Figure 2. Jablonski diagram of the photolysis of
valerophenone with a quencher present.

13

O-H

k. k M
SO hV > 8* 15C > T* 9 P O

 

 

 

r

Q

So + Q*
O-H 0
k
Ph)‘\/\./ -r > Ph/“\/\/
k
0-H
phz’L§> + BBS/I
kP
OH CH OH H

Figure 3. Photolysis of valerophenone.

14

2) Energy Transfer
The quenching portrayed in the Jablonski diagram,
in fluid solutions, is a collisional interaction process

and depends on the spatial overlap of the orbitals of

54,55

the two molecules. It has often been assumed that

triplet energy transfer was diffusion controlled and thus

dependent only an the viscosity of the solvent.56

Quenching rates were calculated using the modified Debye

Equation 8:57

kq = kdiff = '2%%%_fi l/mole°sec (8)

In viscous solvents, the quenching rate has been determined

54 In

to be inversely proportional to the viscosity.
solvents of lower viscosity the rate still increases with

decreasing viscosity but becomes lower than kdiff (Figure 4).

 

 

1/n

Figure 4. Dependence of kq on low viscosity solvents.

15

Wagner proposed that in solvents of low viscosity diffusion

apart competes with energy transfer (Equation 9).

 

. k
D*+A, d1ff> (DNA) —e—t>D+A* (9)
\
-diff

 

Support for the idea that the energy transfer depends on

a common process, i.e. the rate of diffusion together, comes
from the observation that as long as the energy difference
between a wide variety of donors and acceptors is l kcal

exothermic, the rate for quenching in benzene is S 1 l x 109

M.1 sec-1.S4

3) Determination of Reactivity

Since photochemical studies are normally done under
steady state conditions, the measureable quantities of a
particular process are quantum yields for product formation
or light emission. The quantum yields, with quencher

present, for the type II process can be expressed as a series

of probabilities (Equation 10).1

¢II = ¢isc¢BR¢p = ¢isc[kr/(kr + kd + kq[Q])][kp/(kp + k_r)]

(10)

16

¢isc may be dropped from the expression since it is close

to unity for alkyl phenyl ketones. The Stern Volmer

expression (Equation 11) has been derived elsewhere.S7

¢0 is the quantum yield for a process in the absence of

¢O/¢ = 1 + qu[Q] (11)

quencher, ¢ is the quantum yield in the presence of quencher,
[Q] is the quencher concentration, and r is the lifetime of
the particular excited state being quenched. The Stern

Volmer plot will be linear under various conditions.58

4) Effect of Revertible Hydrogen Transfer

The expression kp/(k_r + kp) in Equation 10 is due
to the probability of disproportionation of the biradical
back to starting ketone. Wagner demonstrated that Lewis
bases appreciably enhanced type II efficiency and
attributed it to hydrogen bonding of the hydroxyl
biradical intermediate. If it is found that the quantum
yield becomes unity upon addition of increasing amounts
of hydrogen bonding solvent, then it is possible to say
that kr = 1/10.

If however, the maximum quantum yield does not reach
unity, or within experimental error, then kr # l/To. In
this case, Equation 12 is appropriate.

- = 12
¢max - kr/(kr + kd) kTT ( )

17

T is obtained from a Stern Volmer plot and ¢max is the
maximum quantum yield in the hydrogen bonding solvent.
The value for radiationless decay, kd, may then be computed

from Equation 13.

Rd l/T - k (13)

RESULTS

A. Absolute Type II Quantum Yields

Absolute quantum yields of substituted acetophenone
formation were determined for 3130-R irradiation of
degassed solutions of the ketones listed in Table l. The
formation of substituted acetophenone relative to a known
concentration of an internal standard was analyzed by
vapor phase chromatography (VPC). Valerophenone
actinometry was used with its type II quantum yield known

59

to be .33 for a .1M solution in benzene. The values

for para- and meta-methyl valerophenone agree with results
44

obtained earlier in this laboratory. However, the values

for meta and para-methylbutyrophenone are lower than those

13’39 The values for 3,5- and 3,4-

reported by Pitts.
dimethyl substituted ketones have not been previously

recorded.

B. Cyclobutanol Quantum Yields

The cyclobutanols that are referred to in this study
were not isolated and directly identified. However,
cyclobutanols are known to always accompany elimination.1

The presumed cyclobutanols were formed in the expected

18

19

yields of 5 to 25%, and possessed appropriate VPC

retention times.43’44

Two peaks attributable to the

gig and EEEEE isomers from the substituted valerophenones
appeared on the VPC traces (Figure 14). Since the
presumed cyclobutanols from the buterphenones appeared
under the tail of the parent ketones, the ketones had to
be photolyzed to almost complete conversion to provide

measureable ratios for quantum yield determinations. Data

for cyclobutanol formation appears in Table l.

C. Stern Volmer Quenching Slopes

The Stern Volmer quenching slopes were obtained by
varying the amounts of quencher in succeeding solutions
and plotting the ratio of quantum yield with no quencher
over quantum yield with quencher against quencher
concentrations. 2,5-Dimethyl-2,4-hexadiene was the
quencher of choice for this study. Stern Volmer plots
were linear for ¢O/¢ values of 1 to 3, the region of study.
Previous work has demonstrated the linearity of the plots
for similar ketones out to large ¢o/¢ values.49
Experimental qu values are found in Table 1 and the
corresponding plots in Figures 6 through 10. The k r

q
value for para-methylvalerophenone was a repeat of earlier

work and agrees with the previously determined value.50
For a reason not discernable, the scattering of data points
for the Stern Volmer plots of para-methylbutyrophenone

was particularly large and therefore the plot in Figure 7

20

represents the average of three runs. The Stern Volmer
plot for 3,4-dimethy1butyrophenone (Figure 6) contains
the data points for two runs. The other qu values were
the result of one run plus a preliminary point used to
estimate the desired concentration range. The qu's
represent the average of the individual points and the

average deviation is given.

D. Solvent Studies

Maximum quantum yields were obtained for the ketones
by gradually increasing the concentration of an added
Lewis base in solutions of 0.1M ketone in benzene. With
added t-butyl alcohol, the quantum yields for several
ketones were found to decrease at higher concentrations,
after having reached maximum values (Figures 11 and 12).
Pyridine has then chosen for its increased basicity and
lower polarity. However, in some cases the quantum yields
also decreased at higher pyridine concentrations. This
effect will be discussed later. The values given in
Table II for ¢max are the result of enough data points
(either one or two runs) to yield a plot that either had

a maximum or leveled off. The data are listed in Table II.

E. Dependence of Quantum Yields on Ketone Concentration
Figures 4 and 5 show the variation of type II quantum
yields with changes in ketone concentration. Earlier work

had shown that quantum yields normally rise with increasing

21

ketone concentration because of increasing solvent

50

polarity. A decrease could indicate either the

presence of a quenching impurity in the ketone or

quenching by ground state ketone.59’62

Aspects of this
will be discussed later. The results are listed in the

last section of the kinetic data.

F. Disappearance Quantum Yields
It was necessary to find out whether the ketone was
decaying to some other product(s) and therefore lowering

the ¢ yield. This was accomplished by comparing the

max
parent ketone to standard ratio before photolysis to the
parent ketone plus the summation of type II and cyclo-
butanol formation after photolysis. The results are
given in Table l as a percentage difference. It was
assumed that olefin is formed in the same yield as aceto-

phenone and that the VPC response of each cyclobutanol

equalled that of its isomeric starting ketone.

G. UV Absorption of Methylated Butyrophenones

Table 3 lists the Am and corresponding molar

1

3X

extinction coefficients of the La band of methylated
butyrophenones. The second column in Table 3 lists the
difference, in kcal, of the Amax relative to that of
butyrophenone itself. The uv absorption curves are

given in the last section.

22

um can v mousuwu scum wouaqonaauxo one: mwmoaucoumd a“ no: mosua>

.«ma 0» ca. mm :ome one: muwsfin uouun

A

mwmq mu :oxau one: mumswu nouhmu

m

mxuwmuo>wca oumum camwnuwz .cocwaasaou .m .< mo mwmoze .o.nm on» scum coxmho

“acmuwwvmuuw noumu was ouomon
- oucafian mama :« :ofiumsuom Hocwuanoauxu one an onxu An you vouczouua we: ocouox mcfiuuaum acouuomv

"newumuucoucou acouox z a. «a mosun>u

a

.HIUQW HO: “OH x H a m . “A

a

"oaoam mcwcucosc uoEHo>-:uouw ecu mw » an

 

 

 

o ewe. macm.v an. SN. . n.v cm . SAHH o:o=u:aoaodm>H»;oeeue-v.n
~ cue. do. . ma. .o. .na. con . omoo o:o=ueaoux~=n~xguosue-c.n
a «me. No. . on. v. . m.nH a” . com ococogaouu~a>~xguusae-m.n
ma mac. mama.v n“. H. . o.“ aSN . ooan oaocogaouxoaaflxguoefie-m.n
o who. n. . an. n. . m.m~ o . SAN ococoga020Ha>nguos-asaa
o ado. waw~.v AN. H. . e.“ oov . coon ococucdouxusnaxguoe-uuun
s ova. n. a mm. oo.~ « o.mn oe « mNH o:o:o:mouo~m>ax;uoe-auofl
a NAS. «Ha. . «a. q. . «.4 cc“ . sea“ ocoaogaouxuanasguos-uuos
engagmfim 2.: .... . s
whouoaauum ouuocwxouosm .H oanuh

23

.ocoNcon can

 

 

 

 

 

 

 

 

 

0N. NN. NN. mN. aN. NN. No. oaoaonaouspaonguoeHe-m.N
NV. Ne. av. on. Hm. NH. n.. Hm. NH. NH. oaocugaouxuagHsguoa-auua
JOH do.” ]d ”J 3 Hal 1
en. mm. «H. .mm. N4. 04. ... He. an. NN. .H. neocoaaousuaanguos-uHon
#1. m... S. clan HI qfiIIJIII
HocHeHuxa eaves eH HH._
an. ce. cc. Nn. Hm. NH. ocoaoHQOHNH=onauusHe-v.H
04114 8. we. all
me. me. me. an. me. on. «cocogaouoHa>HsguosHe-q.n
Ho. cm. mm.. ow. ow. 4N. ococogaouoHa>HseuoeHe-m.n
4N. mNN. .N. No. co. mm. ococogaoHoHa>nguos-uHon
andawl. o.¢ o.N m.N o.u, N.H o.H, mo. o qu. madam»
HHonouH< HNH3N-H woven cH HH._
«mowvzum u=o>Hom now swan .~ ounuh

24

Table 3. Substituent Effect on the 80 + lLa Transitions
of Acylbenzenes

 

 

 

Butyrophenonea
Substituent
Amax’ nm -Av, Kcal/mole

H 238 (14,000) 0

m-CH3 240 (11,000) 1.0

p-CH3 245 (18,000) 3.3
3,4-dimethy1 247 (15,000) 4.2
3,5-dimethy1 244 (11,400) 2.8

a

in heptane; molar extinction coefficients in parenthesis

25

 

 

 

.30
4’11 .20 O
{3
.10
1 I
.1 .2
[Ketone]M

Figure 5. Relationship of type II quantum yield to ketone
concentration 6 p-methylbutyrophenone,
C] 3,4-dimethy1butyrophenone, A 3,5-dimethy1-

 

 

 

 

butyrophenone.
.40
0
II .30 S
.20 4‘
I I
.1 .2
[Ketone]M

Figure 6. Relationship of type II quantum yield to ketone
concentration; . _m-methylvalerophenone ,

Cl 3, 5-dimethy1valerophenone, ‘ 3,4-dimethyl-
valerophenone.

 

 

Figure 7.

26

I

I V _4
4 5 [QxlO ]M

q

Stern Volmer quenching plots for Q 3,4-dimethyl-
butyrophenone, C]3,5-dimethy1butyrophenone.

27

 

 

 

 

3-
9
2" i
1....
I I 1 l
1 z 3 4
[Q x 1041M

Figure 8. Stern Volmer quenching plot for
p-methylbutyrophenone.

ale
0

 

 

I I F l

l 2 3 4
[Q )5 103 M

Figure 9. Stern Volmer quenchIng p ot for
3,4-dimethy1valerophenone.

2.5-1

2.0“

1.54

 

 

I I I I

6 10
[Q x 1041M

N!
A

Figure 10. Stern Volmer quenching plot for
meta-methylbutyrophenone.

29

 

 

3.o~
2.5- ‘
2.04
1.5-4
1.0-
T I I I
1 2 3 4
[Q x 1031M

Figure 11. Stern Volmer quenching plots for
Q para-methylvalerophenone,
A 3 , 5- dimethylvalerophenone .

30

.ozonozaouxpsnaxnuos-muoz .ococogm
-onxpznflxnuoswv-e.mAv .oaoco:QOHoHu>Hxnpoefiv-e.m_U .ococonmohoaw>
-Hxnuosg-m.m‘ .ococogmonofimzcfiuosépos O .2823 H: Hogooaw

axusn-u mo mucsoem venue op caofix expanse HH maze mo dwnmcowumaom .NH ohswfim

.ucou Honooam qusn-u

 

 

 

 

 

 

 

o.mI m.v o.v n.n D.M m.N o.~ m.H o.H m.
LIIITII
n.
O o\
< 0' u.
4 .
J‘
IIJ I H
c

 

 

31

 

 

.6 ‘
.5 -
. C
.4 -
811 I
.3 - ' E:
U N
.2
.1
II
' 1 TV I T r
.2 .4 .6 .8 1.0 1.2
[Pyridine Concentration]
Figure 13. Effect of pyridine on type II reaction in

benzene . Q meta-methylbutyrophenone ,

Apara-methylEutyrophenone, C] 3,5-dimethyl—

butyrophenone.

DISCUSSION

A. Effects of Methyl Substitution on Reactivities and

Radiationless Decay of Triplet State

As previously discussed, the reactive state of the
alkyl phenyl ketones is usually the triplet, due to the
high effic1ency of isc from the lowest 1(n,n*) state 0f
the excited singlet to the nearby 3(1r,1r*) state of the
triplet. In solution, the only competing modes of decay
from the triplet W111 be hydrogen abstraction and
radiationless decay. Wagner and Schott have shown that
the hydrogen abstraction most likely originates from the
upper 3(n,n*)state of ketones which possess lowest 3(1r,1r*)

triplet states.51

The type II system was chosen for study
because the effects of the substituents on the excited
states may be readily measured through the change in the
reactivity of the triplet towards hydrogen abstraction.

If the reactivity 15 coming from an upper n,n triplet in
equilibr1um with a lower n,n triplet, a parallel effect
should be observed between the reduction in reactivity and

the increase in the separation of the excited triplet

states. Since the rate of hydrogen abstraction is

32

33

independent of kd’ and if one can assume an insignificant
change in kq with substitution, then experimetal kr values
will represent the change in reactivity of the triplets.
The 1/1 values from the Stern Volmer plots will give the
sum of the rates of decay from the triplets. Equation 12
indicates that if we know the maximum total quantum yield
for product formation then kr and kd values may be
determined. To eliminate any inefficiency in product
formation due to the reversal of the hydrogen abstraction
process, a hydrogen bonding solvent was added. Figures 11
and 12 demonstrate that a maximum is reached in the 011
value in the addition of the Lewis bases, t-butyl alcohol
and pyridine. At this point, the value for the probability
of the biradical going to product is presumably unity, and
0 = krT. Ketones such as valerophenone and butyrophenone

max

which have a ¢ma of unity must possess radiationless decay

x
rates which cannot compete with the rate for hydrogen
abstraction. Therefore the l/T obtained from the Stern
Volmer slope will equal kr' The ¢max values from Tables

4 and 5, and Figures 11 and 12, indicate that all of the
ketones in this study possess kd rates which do indeed
compete with hydrogen abstraction and the extent of this
competition varies. The decrease 1n ¢IImax at high alcohol
concentration is probably due to the increasing
competitiveness of the radiationless decay via an increase
in the separation of the triplet states with the increasing

63

polarity of the solvent. The decrease when pyridine was

34

Table 4. Substituent Effects on Triplet State
Reactivities of Butyrophenone

 

 

Ketone ¢maxa kr x 106b kd x 106C rela:ive
butyrophenone 1.0d 7.6d - 1.0
maaa-methyl .60 t .085 2.7 . .4 1.3 .35 . .03
Raga-methyl .69e .97 t .15 .45 .14 t .02
3,5-dimethyl .32 t .02 .51 t .05 1.1 .067 r .009
3,4-dimethy1 .43 . .030 .35 t .003 .48 .045 t .005
p-methoxy .04f .06 1.5 .008

 

aIncludes 011 plus ¢(cyc) , all at .lM ketone;
max

bobtained from equation 12;

max

Cobtained from equation 13;

dvalue taken from A. E. Kemppainen's Ph.D. Thesis,

Michigan State University;

8This value is an 18% increase from experiment value due
to increase in 011 in later runs after purification;

fObtained from Ph.D. Thesis of H. N. Schott,
Michigan State University.

35

 

 

 

Table 5. Substituent Effects on Triplet State
Reactivities of Valerophenone

Ketone 0 a k x 106b k x 106C relative

max r d k

1r
d d

valerophenone 1.0 122 - 1.0
meta-methyl .84 t .07 32 t .5 7 .25
para-methyl 1.0d 18.5 . 1.4 m .45 .15 . .01
3,5-dimethyl .65 t .05 9.0 t 9 4.7 .074 t .007
3,4-dimethy1 .80 i .06 3.4 t .4 0.9 .028 t .003
p-methoxy .26e .56 1.6 .005
aIncludes IImax plus (cyc)max, all at .lM ketone;
bobtained from equation 12;

Cobtained
d

from equation 13;

value taken from A. E. Kemppainen's Ph.D. Thesis,

Michigan State University;

eObtained
Michigan

from Ph.D. Thesis of H. N. Schott,
State University.

36

used might be attributed to charge transfer quenching, if
the ionization potential of pyridine is low enough.64
Any discussion of the effect of substituents on
reactivity would not be complete without the presentation
of spectral data, i.e., how the substituents affect the
relative energies of the triplet states. The data from

1

Table 3 indicate that the La state is stabilized to a

greater extent by a methyl group in the para position.
Progressive methylation also lowers the 3(n,1r*) energy, as

demonstrated by Yang's phosphorescent studies.22

His work
points to a destabilizing effect on both the 1(n,n*) and
3(n,1r) from methylation in the papa position, whereas the
aapa-methyls show little effect on the (n,n*) states. The
result of this is a larger (n,n*)-(n,n*) triplet separation
for the 3,4-dimethy1 ketone relative to the same separation
in the papa and 3,5-dimethy1 isomers (Table 6). By analogy,

the meta-methyl ketone should have a smaller triplet

separation than the para. Although the spectroscopically

Table 6. Phosphorescent Excitation O-O Bands of Several
Methylated Acetophenonesa

hump-30m)

 

Ketone n-n* -nm- n,n* kcal
p-Methylacetophenone 386 368 3.7
m-Methylacetophenone N384b N372b 2.4b
3,4-Dimethy1acetophenone 392 367 5.0
3,5-Dimethy1acetophenone 390 371 3.7

 

3Reference 22

bextrapolated values

37

determined triplet energies are higher in a polar glass
than in solution, the relative energies should be very
nearly the same. In a non polar solution, the energies of
the papa- and papa-methyl (n,n*) and (n,n*) triplets must
be very close and the nature of the lowest triplet is not
agreed upon.47’53’65
Data for methoxy and methyl ketones has shown that the
papa isomer has a shorter lifetime and smaller quantum

yield than the para isomer.SO

The 411 and 1/T values in
Table 1 agree with these results. kd values for the
3,5-dimethy1ketones are observed to be slightly lower than
those for the papa-methyl ketones. The origin of this
effect is not clear. The radiationless decay rates of the
papa-methyl ketones and 3,4-dimethyl ketones lie within
experimental error of coinciding. There is a large drop

in the kd rate upon the placement of a papa group on the
papa-methyl ketone. It follows that the placement of a
methyl group at the papa position has the predominate
effect on ka. Yang found that methylated acetophenones are
less reactive than acetophenone, which has a lowest (n,n*)
triplet, and also exhibit slower nonradiationless decay
processes.22 Here again the papa and 3,4-dimethy1ketones
had similar kd rates, with the rate of the 3,5-dimethyl-
ketone being slightly faster. Any conclusive statement
about the rates of radiationless decay in the present study
is prevented by the scatter of the rates of decay data.

The general conclusion is that the meta isomers have the

38

higher kd values. The data seem to indicate that the kd
value is larger when the lowest state is more (n,n*) like.
However, the larger kd value may also be the consequence
of quenching by the ground state ketone. Such quenching
has been demonstrated Wlhh papa- and papa-methoxy aceto-

phenones.59

This data must be cautiously viewed since the
three ketones had similar triplet energies. This type of
decay has also been demonstrated for Michler's ketone and

60’61 The concentration studies in

Michler's thione.
Figures 4 and 5 indicate no general self quenching effect
in either series of ketones and therefore the slopes most
likely represent the presence of a quenching impurity,
which is also the probable origin of the scatter in the

kd data. Since papa-methoxyvalerophenone displayed such a
large value for radiationless decay, any self quenching
mechanism would also have to show up in a concentration
study. However, a slight increase in 011 with increasing
ketone concentration actually occurs, making the self
quenching proposal less likely. The rate of self quenching

that was proposed for the methoxyketones (8 x 108M-lsec'l)

would surely be competitive here.59
The values of the kr from Tables 4 and 5 indicate

that the papa isomer is more reactive in hydrogen

abstractions than the papa. This is reasonable considering

the earlier statement that the meta and para-methyl both

slightly stabilize the (n,n*) levels, the para more than the

39

papa, whereas the papa methyl has a small effect on the
(n,n*) and the papa significantly destabilizes it. This also
is true in the case of the 3,4 and 3,5-dimethy1ketones.

The papa substitution might also be less effective in
decreasing the electrophilicity of the reactive triplet.

The relative kr values demonstrate a progressive
decrease in reactivity for the series of methylated butyro-
and valerophenones. The last entry in Tables 4 and 5 show
that the effect of a single p-methoxy group is much larger

than that of dimethyl substitution.

B. Additivity of Substituents Effects

A systematic investigation of the additivity of
substituents on excited state reactivity has not, to the
author's knowledge, yet been reported. If the average of
the relative reactivities for both series of ketones 15

compiled (Table 7) the results qualitatively indicate the

Table 7. Additivity of Substituent Effects on Reactivities

 

 

 

 

Average Predicted

Substituent Relative kr Additivity

H 1 -
p-Methyl .30 t .03 -
p-Methyl .14 1 .02 -
3,5-dimethyl .070 t .009 .0903
3,4-dimethyl .037 t .005 .042b
a0.3 x 0.3; b0.3 x 0.14

40

occurrence of such an additivity pattern in this system.
The correlation is admittedly rough, but this is very
probably the result of accummulative experimental error.
A reasonable correlation is observed in Yang's data
(Table 6) on the effects of methylation upon the

22 The last

phosphorescence emission from acetophenones.
column in the Table 6 lists the splitting in the triplet's
energies, which is at least proportional to what it should
be in solution. It would be informative to also have the
experimental values for the papa isomer. The values for
the 3,4 and 3,5-dimethyl ketones are what would be expected
if they were to be correlated to the reactivities. This

is also what would be expected if the reaction was
originating from a thermally equilibrated upper (n,n*)
triplet. It would be helpful to be able to get
phosphorescent data in a non polar glass. Although the
values listed in Table 8 cannot be compared to the
reactivities, they do indicate that the effects on the
lowest 3(1r,1r*) state seem to be additive. It would now

be interesting to see if the 3,4,5-trimethy1ketone and

also different groups would display parallel additive

behavior.

41

Table 8. Additivity of Substituent Effects in
Spectroscopic Data.a

 

 

 

Phosphorescence Av Expected
Substituent Emission in kcal Correlation

H 386 0
P 392 1.0
M 394 1.4

3,4- 400 2.4 2.4b

3,5-e 402 2.9 2.8C

3,4,5- 406 3.6 3.8d

 

d

3From reference 23; b1.0 + 1.4; C1.4 + 1.4; 1.0 + 1.4 + 1.4.

e
From reference 22.

C. The High Rate of Radiationless Decay of Valerophenones

Examination of the kd values indicate an exceptionally
high kd value for both papa-methyl and 3,5-dimethy1-
valerophenones. Reasonable answers to the high rate would
be an undetected or revertibly-formed product, or more
likely, a quenching impurity. The term revertible is used
because of the absence of any extraneous VPC product peaks
for these compounds.

Peaks of unknown origin in a one or two percent yield
were evident in the VPC traces in the photolysis of the
butyrophenones. Similar products were found by Pitts in
his work with butyrophenones and were attributed to ring

addition by the biradical (Equation 14).13

42

OH 0
(I111
0143—©>—C~CH2 ——-9 ——>
L—' CH 3 CH 3

(14)

D. Summation

l) The reactivity of triplet phenyl ketones is
reduced to a greater extent by a methyl group in the
papa position than by a papa-methyl. This effect is what
would be expected from the differences in the triplet
splitting.

2) The rate of radiationless decay was found to be
larger for the ketones with a single papa methyl group.
The reason for the increase is still not clear.

3) Of the greatest significance, a qualitative
additivity correlation was noted for the effect of
methylation on the reactivities of the triplet. A
parallel was noted with the effects of methylation on
the n,n*—n,n* triplet splitting determined by

phosphorescent excitation methods.

E. Further Studies
1) Further work is needed to discover the reason

for the high kd values in the valerophenones.

43

2) The 3,4,5-trimethy1 ketones need to be studied
to determine if the observed additiV1ty is maintained by
the third group.

3) Studies on varying the types of substituents need
to be completed to determ1ne if the additivity correlation

in the excited state may be extended.

EXPERIMENTAL

A. Chemical
1) Dependence on Purity
For a ketone suCh as 3,4-dimethy1butyrophenone, which

has a solution lifetime of 1.2 x 10-6

sec, a ketone
impurity of .01% could result in a significant amount of
triplet quenching. This would have led to erronious
results for lifetimes and kr values. It was thus
imperative to make certain that the ketones used were
checked (by VPC) very carefully before using. In all
cases, the ketones used were run through a short alumina
column and recrystallized several times from heptane,
pentane, and mixtures of ethanal and heptane. They were
then distilled as carefully as possible on a Nester Faust
model NFT 61 Spinning Band Distillation unit with a
maximum theoretical plate limit of 250. The purification
cycle was repeated until the ketones were considered
suitably pure by VPC analysis. The qualification for
purity was no observable impurity greater than .005%.
2) Preparation of Ketones
a) Method I - The ketone was prepared by using a

dropwise addition of a relative mole ratio of .12 moles

44

45

of the Grignard of a n-bromo alkane to .1 mole of the
respective methylated benzonitrile in 200 ml of ether.
The resulting imine salt was carefully stirred into
300 gm of ice containing 30 ml of concentrated HCl. The
aqueous layer was extracted with ether or benzene to
take out any soluble impurities, such as the starting
nitrile. The organic salt was then hydrolyzed to the
desired ketone through a heating period of one half to one
hour. The ketone was then extracted and the organic layer
dried over anhydrous magnesium sulfate. The solvent was
removed and the ketone purified by the given procedure.
b) Method II

The ketone was prepared from the addition of the
correct alkyl lithium compound to the lithium salt of the
methylated benzoic acid on a .1M scale. The lithium acid
salt was prepared from the reaction of the methylated
benzoic acid and lithium hydride in dry T.H.F. The white
salt was formed after a few hours of reflux. The alkyl-
1ithium reagent was prepared from the corresponding alkyl
bromide and lithium suspension with the reaction temperature
kept below -20°C. The alkyl lithium reagent was then added
slowly to the acid salt and refluxed to complete the
reaction and to break up any excess lithium reagent. The
entire procedure up to this point was completed under an
atmosphere of inert gas. The dilithium salt was then

hydrolyzed to the ketone in a well stirred and cooled

46

aqueous acid solution. The solution must be well stirred
to insure the fast hydrolysis of any remaining lithium
reagent. The aqueous layer was then extracted and the
organic layer dried. After evaporation of the solvent,
the resulting ketone was purified.

c) Method II-a

The same procedure was followed as in Method 11
except that the alkyl lithium reagent was added to the
methylated benzoic acid. This procedure resulted in a
large amount of alcohol by-product and therefore was used
only once.

3) Photolysis Products

a) AcetOphenone - (M.C.B.) distilled at 55° @ 3MM.

b) Meta-Methylacetophenone - (Aldrich) used
without distilling.

c) Paramethylacetophenone - prepared by Method I
from acetylbromide (Aldrich) and papa-cyanotoluene (Eastman
Organic) b.p. 47° @ 1.5MM.

d) 3,4-D1methy1acetophenone (Eastman Organic)
b.p. 78° @ 1.5MM.

4) Solvents

a) Benzene - Both Fisher Scientific Co. 99 mole %
thiophene free benzene and Mallinckrodt Nanograde benzene
were purified by stirring with concentrated sulfuric acid.
This was usually performed in gallon quantities. The acid

was changed every day until it remained colorless. The

47

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HH eogooz

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va
Ne.nHNH .Hooe.HH.oH xe-H
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ooHnHeH .He HN.NS ooHNeHe .He eN.HH
uuuxom .Ho mm.H uoHnHuu ohm mumHam
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om.nHNo .Hooo.mH.ov xenH HHe NN.N

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HoHoHoo .He HH.N. HoHueH» .Ho HN.H

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HmUHEonu usz HmnH .moH .oNH ox: mo
mxuoa uoam mmaz Hz: n.~ w UomcH .A.n

ov~xal

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we:

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mxmoa uoam mom: H22 m.~ o oo~o .m.a

new
mm.OHNo .Hooo.eH.ov xeaH "Ho No.N
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HmoHEonu Hez nmHH .Hm .NOH an o\5 mo
mxmon ovum one: “22 o.H w Uo~n .n.n

mama Hmuuuomm new
moHuuoaoud Hmumezm

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ococogmouxuanAAuOIHe-m.n

on wn

o z u o~.osd
ococogqouxusanguoaHv-v.n

oeHzHHu NN.NoH
econozqouxuaonnuos-auoz

 

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unuHoz umHsuoHoz ecu «Hashom

 

mo:0uox voNHmocucxm you mama Hmonxcm

.m oHamh

48

 

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qusa-=
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HHom van :mEoHou

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:omosumz - ovHEouonusn-:
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22 o.N o ooNo .o.a

He we.N

.N.NH oHoeaoee .Ho no.NH ooHoHeo

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.Ho «o.v HoHoHoo one “HHHHo

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oxeon ooom one: “22 N.H o o.ooH .n.o

NeNxea on.NHno

HooN.eH.oH H "He ma.N .NN.N

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.Ho mm.H uquHuu "one mumwgu
HauHEogu usz HmcH .nnH .omH o\6 a.
mxmon uonm moo: H2: o.H w UooHH .n.a

oeN
NHN. .Hooo.HH.oH xoaH "Ho mN.N
.NN.N .oN.NS oHoesoee .Ho Ne.NH
ooHoHeo .He 4.NV ooneHo .He mm.HH
uonHque .ao mm.v uoHQHHu noun
ooHHEm HeoHsoeo 222 “2: N o.He .o.a

meN
emunHNo .Hoon.mH.oH xoaH
"He o.N .HN.N .mN.N .H.NV oHoeeoee
.He N.Nv ooHoHeo .He mH.NS ooHueHn
.Ho Nm.HU ooHoHoHoe .He eoH.
uoHnHuu "one mumHam HaoHaosu as:

ov-

oeHzHHo NN.NoH
ococogmouoHa>
oonnHu .N.ooH

ococognouoHa>chuoiHn.m.n

oeH=NHu eN.ooH

ocosogaouoHa>nguoaHn.v.n

oonNHu NN.oNH
ococoznouuHa>nguos-uuoz

 

Cow -

z u -.oNH
ococonaoHoHa>nguos-uuum

 

 

uoHHdaam can
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«an: Hauuuonm
can moHuuonoum Hauwmxgm

usuHoz uuHsuoHoz van «Ha-non

 

avosauucouv

.m Ounuh

49

benzene was then washed with a NaHCO3 solution followed by

a saturated NaCl solution. After being dried with anhydrous
magnesium sulfate, the benzene was distilled at atmospheric
pressure from 100 to 200 grams of phosphorous pentoxide
through a 49 cm. glass helix packed column. A high reflux
ratio to head takeoff was maintained. A forecut and endcut
of 10 to 15% was not used.

b) t-Butyl alcohol - The t-butyl alcohol (Fisher
Scientific Company) was refluxed and distilled from
freshly cut sodium after one recrystallization from itself.
It was pure enough to crystallize at room temperature.

c) Heptane - The heptane (Matheson Coleman and
Bell) used was purified in a mannor analogous to benzene.

d) Pentane - The pentane (Matheson Coleman and
Bell and J. T. Baker) was purified in a mannor analogous
to benzene.

e) Pyridine - The pyridine (Mallinckrodt Chemical
and Fischer Scientific Company) was distilled from barium
oxide at atomspheric pressure.

f) Ethanol - 95% Ethanol (Supplier unknown) was
refluxed and distilled from magnesium at atmospheric
pressure.

5) Internal Standards

a) Tetradecane - Tetradecane (Columbia Organic
Chemicals) was purified in a mannor analogous to benzene
and was distilled at reduced pressure. It was purified

by Professor P. J. Wagner.

50

b) Pentadecane - Pentadecane (Columbia Organic
Chemicals) was purified in a mannor analogous to benzene
b.p. 92°C @ lMM.

c) Hexadecane - Hexadecane (Aldrich Chemicals)
was purified in a mannor analogous to benzene. b.p. 108°C
@ 1.1MM.

6) Quenchers

a) apa-l,3-Pentadiene (piperylene) -

Piperylene (Chemical Samples Company) was used as received.
Analysis (V.P.C.) showed it to contain only 0.4% of the
ppapa isomer.

b) 2,5-Dimethyl-2,4-hexadiene -
2,5-Dimethyl-2,4-hexadiene (Chemical Samples Company)
was purified by sublimation at atmospheric pressure at

-10°C.

B. Methods of Analysis
1) Preparing Ketones for Photolysis

a) Making Solutions - All solutions were made
up using Class A volumetric glassware and an analytical
balance sensitive to .0001 gm, at room temperature. A
stock solution of ketone and standard was made and the
required amount pipetted into individual flasks. For a
quenching run, a stock quencher solution was prepared and
the required amount then pipetted into the same flasks.
For a solvent study, the required amount of Lewis base

was weighed, in the case of pyridine, or pipetted from a

51

stock solution, in the case of t-butyl alcohol, into the
individual flasks. The flasks were then filled to the
mark with benzene and mixed well. Two 2.8 ml samples were
then injected into pyrex photolysis tubes with a 5 ml
hypodermic syringe. The tubes had been previously
prepared by selecting cleaned pyrex 100 x 13 MM culture
tubes, which met a set standard of width and lip
deformation, and drawing out the heated tubes to give
them a cappillary neck about 2 cm from the open end of
the tube.

b) Degassing - The tubes were then attached to
a vacuum line using no. 0,0 one hole rubber stoppers on
individual stopcocks. The tubes were slowly frozen,
emmersed into liquid nitrogen, and pumped to a vacuum

3 to 10'4

of 10- MM. The stopcocks were then closed
and the tubes allowed to thaw. The process was repeated
five times and on the last cycle the tube was sealed off
at the cappillary.

2) Photolysis

The tubes were then placed in a "merry-go-round"
apparatus which was designed to ensure that each tube
received an equivalent amount of light and was kept at

the same temperature.66

A 450 watt medium pressure
mercury lamp was inserted into a water cooled quartz
jacketed immersion well. The well was placed into a
cyclindrical vycor jar allowing a 1 cm path through a

.002 M potassium chromate 1% potassium carbonate filter

52

solution which isolated 3130 A radiation.66

The samples
were photolyzed till a 4 to 10% conversion to product
occurred. All quenching runs and solvent studies contained
.lM ketone. Valerophenone actinometer tubes were sometimes
irradiated to 10% conversion. Earlier work showed that the
quantum yield was not affected.44
3) Analysis of Photolyzed Solutions
The analysis for product formation were all completed
through the use of vapor phase chromatography (VPC). The
work was generally completed on two similar Varian 1200
VPC's equipped with flame ionization detectors and a
Leeds and Northrup Speedomax W recorder. Approximately one
quarter of the work was analyzed using a model 224 disc
integrator, and the rest by an Infotronics Model CRS-208
Automatic Digital Integrator. An Aerograph HyFi Model
600D VPC fitted with a 25' x 1/8" aluminum column containing
25% 1,2,3-tris(2-cyanoethoxy)propane (8,8,8) on 60/80 mesh
Chromosorb P was used in the analysis of a few piperylene
actinometers. All the gas chromatographs had on column
injection and used nitrogen as a carrier gas. The gas
flows for compressed air and hydrogen were set to
maximize the sensitivity of the detector. The nitrogen

flow rate was kept between 15 and 20 ml/minute. The

following columns were used in the analyses.

53

COLUMN 1 9' x 1/8” aluminum filled with 5% QF-l,
1.2% Carbowax 20M on DMCS treated

60/80 mesh A. W. chromosorb G.

COLUMN 2 6' x 1/8” aluminum filled with 4% QF-l

1.2% Carbowax 20M on 60/80 chromosorb G.

COLUMN 3 11' x 1/8” aluminum filled with 4%QF-l
1% Carbowax 20M on 80/100 DMCS

A. W. chromosorb G.

COLUMN 4 8 2/3' x 1/8" aluminum filled with 4% QF-l,

1% Carbowax 20M on 60/80 chromosorb G.

4) Product Identification

The methylated acetophenone products of the photolyses
were identified by the retention time of the known compound.
The peaks which appeared in the VPC trace after photolysis
near the parent ketone was presumed to be the cyclobutanol.
Separation and identification of cyclobutanol products has
been shown, therefore it was felt that further identification

was not necessary.67’68

Small peaks which appeared near the
acetophenone with three of the ketones were not identified.

Figure 14 is a typical VPC trace.

 

 

\J

Figure 14.

54

 

 

 

 

 

 

 

K) L.)

VPC trace of 3,4-dimethy1valerophenone

a) C16 b) 3,4-dimethy1acetophenone

c) trans and apa cyclobutanols

d) parent ketone; integration was
accomplished using the automatic
integrator

SS

5) Standardization Factors

To eliminate the error introduced by VPC injection
technique, an internal standard was placed into the
solution to be photolyzed. The VPC area for the photo-
product (PP) may then be compared to the area of the
internal standard (IS). However, a standardizing factor
(SF) needed to be introduced to account for the differences

in molar response ratios, which Equation 15 depicts.

[PP] = SF[IS](PP)/(IS) (15)

In this expression, brackets indicate concentration and
parenthesis indicate VPC areas. The S.F value was
determined by weighing out exact amounts of standard and
photoproduct and determining the VPC response ratio

(Equation 16).

SF = [PP]/[IS] x (IS)/(PP) (16)

The value of (IS)/(PP) was the average of six VPC injections.
6) Actinometry
The amount of light impinging upon the solutions
during photolysis was usually determined by valerOphenone
actinometry. Actinometer tubes contained .lM valerophenone
and ~.003 M tetradecane in benzene. The concentration of
ketone used in all photolyses was large enough to absorb

>99.9% of the incident light. For several runs, a .1M

56

solution of acetOphenone and a varying concentration of
piperylene in benzene was used as the actinometer. The
kinetics of the expression used are reported elsewhere

Equation 17.69

[pipA]3 = [ala-pip]o 1n[(.555)/(.555-%-trans)] (17)

The analyses were performed on the Aerograph HyFi Model
600 g.c. containing the 8,8,8 column. For an unidentified
reason the light output was found to be higher using the
piperylene actinometry. For the sake of consistancy, all
values are reported relative to those of valerophenone.

7) Ketone Disappearance and Cyclobutanol Yields.

The total quantum yield is determined by the sum of
the acetophenone product and cyclobutanol formation,
therefore the cyclobutanol VPC area must be standardized.
The procedure to procure the SF factor for the cyclo-
butanols entailed the preparation of a solution of carefully
weighed samples of the acetophenone and parent ketone and
obtaining the VPC area response factor. The same procedure
was used in obtaining the said SF value as for the similar
value in the internal standard/acetophenone response. The
values for the various ketones are recorded in Table 31.
It was also necessary to insure that the photoproducts
mentioned were the only resulting products of the photolysis.
The procedure for determining this was reported in the

results section. The results are reported in Table 32.

57

8) Reliability of Data

The reproducibility of the relative VPC peak areas
is on the order of 15% using the model 224 integrator and
within 11% for the digital integrator. The uncertainty
for making the solutions and filling the tubes was on the
order of l to 2%. Altogether, the uncertainty is within
1S to 8% including the uncertainty in the actinometer.
The uncertainty in the qu values should be less due to
the lack of actinometer error. The variation in results
due to O2 quenching cannot be estimated, though inspection
of the deviation for the higher qu values suggests this
occurrance. Unreliability due to quenching impurities in
the glassware was reduced as much as possible by soaking

in a commercial cleaner, rinsing 10 times with hot water,

and rinsing 10 to 15 times in distilled water.

KINETIC DATA

A. Quenching Studies.

The following tables contain quencher concentrations,
relative vpc areas of acetophenone type product relative
to standard, the standard used, and its concentration.

A reference to the column used and temperature of the

column will be given.

58

Table 10. Stern-Volmer Quenching of .l M

59

ara-Methyl-

butyrophenone by 2,5-Dimethy1-2, - exadiene.

 

 

Run #1
Quencher Product/Standard

Concentration Ratioa [AP] ¢o/¢

0.0 .634 .00639 1.0
.0002 .372 .00375 1.70
.0003 .267 .00269 2.37
.0004 .224 .00225 2.83

 

a
0.00517 M C15

internal standard.

Column 4 - 132°C.
Incident Radiation .0296 Einstein/8.

 

 

 

Run #2
Quencher Product/Standard
Concentration Ratioa [AP] ¢o/¢
0.0 .556 .00559 1.0
.0002 .320 .00322 1.74
.0003 .300 .00302 1.85
.0004 .240 .00241 2.31
3.00516 M C internal standard. Column 4 - 132°C.

15

Incident Radiation .0252 Einstein/8.

 

 

 

Run #3
Quencher Product/Standard
Concentration Ratioa [AP] ¢o/¢
0.0 .594 .00600 1.0
.0001 .440 .00444 1.35
.0002 .332 .00335 1.78
.0003 .319 .00322 1.86
.0004 .262 .00265 2.27
3.00520 M C Internal Standard. Column 4 - 133°C.

15

Incident Radiation .0237 Einstein/2.

60

Table 11. Photolysis of meta-Methylbutyrophenone.

 

 

Cong‘éfi‘t‘iiiion Pmdufifiéiiindard [AP] 8.”

0.0 1.04 .00705 1.0
.0001 .986 .00669 1.09
.0003 .764 .00518 1.35
.0005 .645 .00437 1.65
.0010 .475 .00322 2.12

 

a.00348 C15 internal standard. Column 3 - 135°C.
Incident Radiation .046 Einstein/8.

61

Table 12. Photolysis of 3,4-Dimethy1butyrophenone.

 

 

Run #1
Quencher Product/Standard
Concentration Ratioa [AP] q’o/¢
0.0 .258 .00136 1.0
.00005 .217 .00114 1.19
.0001 .153 .00080 1.67
.0002 .121 .00060 2.13

 

3.00301 M C16 internal standard. Column 1 - 129°C.
Incident Radiation .0216 Einstein/2.

 

 

Run #2
Quencher Product/Standard
Concentration Ratioa [AP] 450/¢
0.0 .338 .00308 1.0
.0002 .153 .00140 2.21
.0004 .106 .0097 3.19
.0005 .081 .00074 4.17

 

3.00522 M C16 Internal Standard. Column 4 - 148°C.

62

Table 13. Photolysis of 3,S-Dimethylbutyrophenone.

 

 

 

Quencher Product/Standard
Concentration Ratioa [AP] ¢o/¢
0.000 .902 .00776 1.0
.0001 .344 .00296 1.26
.0002 .266 .00229 1.63
.0003 .230 .00198 1.88
.0004 .182 .00157 2.38
.0005 .200 .00172 2.17
.0006 .165 .00142 2.98
3.00506 M C15 internal standard. Column 4 - 133°C.

Incident Radiation .0308 Einstein/l.

63

Table 14. Photolysis of .l M Para-methylvalerophenone.

 

Quencher Product/Standard

 

Concentration Ratioa [AP] ¢ol¢
0.0 0.353 .00348 1.0
.002 0.226 .00223 1.56
.003 0.194 .00192 1.82
.004 0.174 .00172 2.03
.005 0.150 .00148 2.35
.006 0.138 .00136 2.56

 

 

3.00506 C15 internal standard. Column 4 - 133°C.
Incident Radiation .0111 Einstein/2.

64

Table 15. Photolysis of .1 M 3,S-Dimethylvalerophenone.

 

 

Run #1
Quencher Product/Standard
Concentration Ratioa [AP] ¢ol¢
0.0 1.15 .00676 1.0
.001 .850 .00500 1.35

 

3.00336 M C16 internal standard. Column 1 - 125°C.
Incident Radiation .0228 Einstein/z.

 

 

 

Run #2
Quencher Product/Standard
Concentration Ratioa [AP] 4’o/"’
0.0 .770 .00402 1.0
.002 .441 .00230 1.75
.003 .372 .00194 2.07
.004 .304 .00159 2.53

 

a.00298 M C16 internal standard. Column 1 - 125°C.
Incident Radiation .0132 Einstein/8.

65

Table 16. Photolysis of .l M 3,4-Dimethy1valerophenone.

 

 

Run #1
Quencher Product/Standard
Concentration Ratioa [AP] ¢o/¢
0.0 .42 .00247 1.0
.0005 .26 .00153 1.6

 

a.00336 M C16 internal standard. Column 1 - 129°C.
Incident Radiation .0147 Einstein/2.

 

 

Run #2
Quencher Product/Standard
Concentration Ratioa [AP] °ol°
0.0 0.920 .00510 1.0
.002 0.265 .00147 3.45
.003 0.212 .00118 4.35
.004 0.166 .00092 5.55

 

3.00317 M C16 internal standard. Column 1 - 129°C.
Incident Radiation .0172 Einstein/2.

66

B. Solvent Studies
Included in the following tables are data for the
formation of type II product versus added alcohol or

pyridine to a solution of the ketone and standard.

Table 17. Solvent Study of a Para-methylbutyrophenone.

 

 

 

Run #1
Pyridine Product/Standard [AP] ¢
Concentration (M) Ratioa II
0.0 .228 .00249 .188
.40 .628 .00685 .514
.60 .615 .00670 .506
.80 .603 .00657 .490
1.00 .567 .00618 .467
1.20 .527 .00574 .434
3.00557 M C internal standard. Column 3 - 133°C.

15
Incident Radiation .0143 Einstein/2.

 

 

Run #2
Pyridine Product/Standard [AP] ¢
Concentration (M) Ratioa II
.05 .646 .00504 .317
.10 .682 .00532 .335
.15 .883 .00689 .434
.20 1.07 .00835 .525

 

3.00400 M C15 internal standard. Column 3 - 133°C.
Incident Radiation .0150 Einstein/8.

67

Table 18. Photolysis of meta-Methylbutyrophenone.

 

 

Run #1
Pyridine Product/Standard [AP] ¢

Concentratlon Ratioa II
.00 .39 .00397 .170
.05 .73 .00737 .32
.10 .88 .00889 .39
.15 .92 .00929 .41
.20 .99 .00999 .44
.25 1.03 .01040 .46
.30 1.05 .01060 .47

 

3.00518 M Cls internal standard. Column 4 - 133°C.
Incident Radiation .0207 Einstein/8.

 

 

Run #2
Pyridine Product/Standard [AP] 0
Concentration Ratioa II
.40 1.28 .0118 .55
.45 1.27 .0121 .54
.50 1.28 .0118 .55
.55 1.26 .0116 .54

 

3.00475 C15 internal standard. Column 4 - 133°C.
Incident Radiation .0216 Einstein/2.

68

Table .19. Photolysis of .l M 3,4-Dimethy1butyrophenone.

 

 

t-Butyl Alcohol Pr°°°§§é§§§°°°rd [AP] 411
0.0 .543 .00334 .127
0.5 1.40 .00862 .327
0.8 1.38 .00850 .322
1.0 1.73 .0107 .402
1.2 1.72 .0106 , .401
2.0 1.66 .0102 .387

 

3.00352 M C16 internal standard. Column 4 - 133°C.
Incident Radiation .0264 Einstein/2.

69

Table 20. Photolysis of 3,5-Dimethy1butyrophenone

 

 

 

 

 

 

 

 

Pyridine Product/Standard [AP] ¢
Concentration Ratio3 11
0.0b .433b .00372b .08b
0.2 .916 .00796 .277
0.4 .965 .00838 .291
0.6 .951 .00825 .287
0.8 .943 .00819 .285
1.0 .902 .00783 .272
1.2 .852 .00739 .257
3.00511 M C15 Internal Standard COLUMN 4 - 133°C;
Incident Radiation .0308 Einstein/2;
b.00506 M 015 and .0536 Einstein/t.
Table 21. Photolysis of meta Methylvalerophenone
Product/Standard
t-butyl alcohol Ratioa [AP] 611
0.0 .813 .00548 .349.
0.5 1.40 .00944 .602
1.0 1.67 .01126 .692
2.0 1.72 .01159 .740
3.0 1.71 .01153 .735
5.0 1.72 .01159 .740
3.00346 M C1 Internal Standard COLUMN 4 - 135°C
Incident Raaiation .0157 Einstein/8.

70

 

 

 

 

 

 

Table 22. Photolysis of 3,4-DMVP
_ Product/Standard
t butyl alcohol Ratioa [AP] 011
0.0 .920 .00510 .277
.5 1.64 .00909 .49
1.0‘ 1.96 .00109 .59
1.5 2.15 .00119 .65
2.0 2.15 .00119 .65
3.0 2.30 .00127 .69
3.00317 M C16 Internal Standard COLUMN 1 - 129°C
Incident Radiation .0176 Einstein/2.
Table 23. Photolysis of 3,S-DMVP
_ Product/Standard
t butyl alcohol Ratioa [AP] 011
0.0 .770 .00402 .304
0.5 1.02 .00532 .403
1.0 1.17 .00611 .462
2.0 1.40 .00731 .553
3.0 1.26 .00658 .498
5.0 1.04 .00543 .411
3.00298 C16 Internal Standard COLUMN 1 — 129°C

Incident Radiation .0132 Einstein/2.

71

C. Variance of Type II Yields with Charges in Ketone

Concentration

Table 24. Photolysis of p-Methylbutyrophenone

 

Ketone Product/Standard Acetophenone

 

 

 

 

 

 

Concentration Ratioa Concentration ¢II
.03 .830 .00557 .227
.06 .781 .00524 .215
.l .613 .00411 .167
.15 .420 .00282 .115
3.00344 C15 Internal Standard ' COLUMN 4 - 133°C
Incident Radiation .0157 Einstein/2.
Table 25. Photolysis of 3,4-Dimethy1butyrophenone
Ketone Product/Standard Acetophenone ¢
Concentration Ratioa Concentration 11
.05 .502 .00309 .117
.10 .543 .00334 .127
.15 .511 .00315 .119
3.00352 M C16 Internal Standard COLUMN 1 - 129°C

Incident Radiation .0264 Einstein/8.

72

Table 26. Photolysis of 3,5-Dimethy1butyrophenone

 

 

 

Ketone Product/Standard Acetophenone ¢
Concentration Ratioa Concentration 11
.05 .674 .00101 . .113
.10 .433b .00383 .072 r.
.15 .302 .00270 .050 57,

3.00511 M C16; b.00506 M C16 Internal Standard
COLUMN 4 - 133°C; Incident Radiation .0157 Einstein/8.

 

Table 27. Photolysis of p-Methylvalerophenone

 

 

 

Ketone Product/Standard Acetophenone ¢
Concentration Ratioa Concentration 11
.05 .808 .00545 f .347
.10 .813 .00548 .349
3.00346 M C15 Internal Standard COLUMN 4 - 135°C

Incident Radiation .0157 Einsteain/t.

Table 28. Photolysis of 3,5-Dimethy1va1erophenone

 

 

 

Ketone Product/Standard AcetOphenone ¢
Concentration Ratioa Concentration 11
.050 .750 .00392 .296
.078 .760 .00397 .300
.100 .770 .00402 .304
3.00298 M C16 Internal Standard COLUMN 1 - 125°C

Incident Radiation .0132 Einstein/1.

73

Table 29. Photolysis of 3,4-Dimethy1valerophenone

 

 

 

 

 

 

Ketone Product/Standard Acetophenone ¢
Concentration Ratioa Concentratlon II
.05 .622 .00672 .354
.08 .570 .00615 .324
.10 .550 .00594 .314
.17 .367 .00396 .208
3.00619 M C16 Internal Standard COLUMN 1 - 129°C
Incident Radiation .0190 Einstein/2.
D. Miscellaneous Data
Table 30. Data for Cyclobutanol Ratios
Compound gzgigghgiggil Regggnse iocigiggghifigie
Araa:§atlo .Eagpgr
3,4 DMVP .237 .82 18 1 2b
3,5 DMVP .214 .82 16 t 2.5b
MMVP .662 .74 14 t 1.5b
MMBP .110 .80 8.8 . 1.5c
PMBP .110 .80 8.8 : 1.5c
3,4 DMBP .094 .82 7.7 : 1.5C
3,5 DMBP .126 .82 10.3 . 1.5c

 

aKetones were irradiated to 20-40%, depending n whether the
retention time of the cyclobutanol was similar to that of
bthe parent ketone's;
Error cited was taken as 110%, due to larger differences
in area ratios and slopes;
Error cited was ~*15% due to the same reasons as in
subscript b.

 

'1‘; 1:

74

Table 31. Standard-Product Molar Response Ratios

 

Area/mole (Standard)

 

Standard/Product Area/mole (Product)
Tetradecane/AcetOphenone 2.0a
Pentadecane/p-Methylacetophenone 1.95a
Pentadecane/p-Methylacetophenone 1.95a
Pentadecane/3,5-Dimethylacetophenone 1.70a
Hexadecane/3,4-Dimethylacetophenone 1.75a

 

3:58

Table 32. Experimental Data for Determining
Disappearance Quantum Yields

 

Ketone Ketone Ketone/Standard Ketone/Standard

 

Ra1i2=8gfg121111111811191811211111)
p-methylbutyrophenone 4.98 5.39
p-methylbutyrophenone 4.69 4.65
3,4-dimethylbutyrophenone 5.08 4.95
3,S-dimethylbutyrophenone 5.60 5.61
p-methylvalerophenone 7.16 6.68
3,4-dimethy1valerophenone 6.41 6.70
p-methylvalerophenone 6.21 6.23
3L5-dimethy1valerophenone 5.37 5.30

 

aError is probably *10%

.6“

.5‘

HF

 

75

m b a) 5.3 x 10'5M
a 5

b) 6.5 x 10' M

 

 

 

 

Figure 15.

 

l 1 I l l
220 240 260 280 300
Absorbtion spectra forzfl p-methylbutyrophenone,

b) p-methylbutyrophenone.
Met ylated valerophenones produced identical spectra.

 

 

5

a) 7.26 x 10- M

 

 

 

 

5

b) 5.56 x 10' M

 

 

Figure 16.

 

r I

T, Ti
220 240 260 280 300 320

Absorbtion spectra for a) 3,4-dimethy1butyrophenone,
b) 3,S-dimethylbutyrophenone.
Methylated valerophenones produced identical spectra.

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IIIII“LIMIHIOIIUIIIIIIIII)mI