31293 01093 0802 llllllllllllllllllllllflllll "M; “ : This is to certify that the thesis entitled AROMATIC SCHIFF'S BASES AND FREQUENCY SHIFTS ON THE C=N STRETCHING MODE UPON PROTONATION AND DEUTERATI‘ON presented by JUAN LOPEZ GARR l GA has been accepted towards fulfillment of the requirements for MS ex 0? giemgdcgree in ([4 Date/4W! /z 77/ 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution MSU LIBRARIES _—;‘—-— RETURNING MATERIALS: Place in book drop to remove this checkout from your record. FINES wil] be charged if book is returned after the date stamped below. AROMATIC SCHIFF'S BASES AND FREQUENCY SHIFTS ON THE C=N STRETCHING MODE UPON PROTONATION AND DEUTERATION BY Juan Lopez Garriga A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Chemistry 1984 ABSTRACT AROMATIC SCHIFF'S BASES AND FREQUENCY SHIFTS ON THE C=N STRETCHING MODE UPON PROTONATION AND DEUTERATION BY Juan Lopez Garriga Unprotonated, protonated and deuterated aromatic Schiff's bases seem to be important for modeling the C=N stretching frequency in porphyrins Schiff's bases and derivatives and for understanding the unexpected increase in the C=N stretching frequency which is observed upon protonation or deuteration of the Schiff's bases. The aromatic Schiff's base models are discussed and compared with analogous aldehydes and unsaturated Schiff's bases. The application of Raman and infrared Spectroscopy are used to determine the C=N, C-NH and C=ND stretching frequencies. Other than the changes in the C=N stretching mode upon protonation, no significant shifts are observed in frequency bands related to the aromatic ring motions. The same kind of behavior is observed in the NMR data obtained for these compounds which suggests that the positive charge does not perturb the aromatic ring substituents uniformly. From these observations, it appears that.protonation effects are localized at the Schiff's base environment. TO CO rmen ACKNOWLEDGMENTS I would like to thank my fellow lab members, in particular, José, Brian, Assad, Tony and Bob for their assistance and I would especially like to thank Professor Jerry Babcock for his guidance and enthusiasm in this project. -iii- TABLE OF CONTENTS CHAPTER LIST OF TABLES O O O O O O O O O O O 0 O O O O O O 0 LIST OF FIGURES O O O O O O O O O O O O O O O O O O O I. II. III. IV. LIST INTRODUCTION. . . . . . . . . . . . . . . . . EXPERIMENTAL. . . . . . . . . . . . . . . . . A.1 Sample Preparation. . . . . . . . . . . A.2 U.V. Measurements and Results. . . . . . A.3 NMR.Measurements and Results. . . . . . RAMAN AND INFRARED STUDIES. . . . . . . . . . A.1 Instrumentation. . . . . . . . . . . . . A.2 N-benzylidene-n-butylamine and Derivatives. . . . . . . . . . . . . . . A 3 2-Naphthalidene-n-butylamine and Derivatives. . . . . . . . . . . . . . . A.4 9-Anthra1idene-n-buty1amine and Derivatives. . . . . . . . . . . . . . . A.5 Benzophenone Schiff's Base and Derivatives. . . . . . . . . . . . . . . SCHIFF'S BASES. . . . . . . . . . . . . . . . A.1 Introduction. . . . . . . . . . . . . . A.2 =N Stretching Frequency in Unsaturated and Aromatic Schiff's Bases. . . . . . . A.3 C=N Stretching Frequency on Protonated and Deuterated Aromatic Schiff's Bases. SIJMMRY AND FUTURE WORK 0 O O I O O O O O I O A.1 Summary. . . . . . . . . . . . . . . . . A. 2 Future work. 0 O O O O O O O O O O O O 0 OF REFERENCES. . . . . . . . . . . . . . . . . PAGE . .vi . .63 TABLE II III IV VI VII LIST OF TABLES Amax(nm) of Aldehydes and Schiff's bases. Chemical shift for carbonyl and imine protons of the kind: ‘,rHa Ha\\C=N’,.CH2(a)R ArC , §§O .Ar” Ha\ C=fi'/CH2 (G)R Ar”C \Hb(D) Raman and Infrared Frequencies for n- benzylidene-n-butylamine (BnBI), n- benzylidene-n-butylammonium ion (BnBIH+ ) and n-benzylidene- n-butyldeuteroammonium ion (BnBID ) in chloroform and methylene chloride. . . . . . . . . . . . . . . . . and Raman and infrared frequencies of 2- naphthalidene-n-butylamine and derivatives. Raman and infrared frequencies of 9- anthralidene-n-butylamine and derivatives. Carbonyl and imine stretching frequency of unsaturated and aromatic compounds. . Raman and IR spectroscopic frequencies for unprotonated, protonated and deuterated unsaturated and aromatic Schiff's bases. PAGE .11 .22 .33 .46 58 66 72 FIGURE LIST OF FIGURES PAGE a. Rhodopsin. b. Bacteriorhodopsin brsyo, all trans-retinal-+opsin. c. Bacterio- rhodopsin br503, all trans-3-dehydro retinal-+opsin. d. Nickel (II) formyl- vinylporphyrin. . . . . . . . . . . . . . . . . . .3 a. N-Benzylidene—n-butylamine. b. N- Benzylidene-n-butylammonium ion. c. 2- Naphthalidene-n-butylamine. d. 2-Naphthali- dene-n-butylammonium ion. e. 9-Anthra1idene- n-butylamine. f. 9-Anthralidene-n-butyl- ammonium ion. g. Benzophenilidene-n- butylamine. h. Benzophenilidene-n-butyl- ammonium ion. . . . . . . . . . . . . . . . . . . .8 U.V. spectra of Benzaldehyde ( ), N-Benzylidene-n—butylamine ( ), N-Benzylidene-n-butylammonium ion t——---—-°-——), and N—Benzylidene-n- butyldeuteroammonium ion ( ----- ) in chloroform. . . . . . . . . . . . . . . . . . . . 13 60- -MHz NMR spectra of Benzaldehyde (BCHO), N- Benzylidene-n-butyl amine (BnBI), N- Benzylidene- n-butylammonium ion (BnBIHI) and N- Benzylidene-n-butyldeteroammonium ion (BnBID) . . . . . . . . . . . . . . . . . . . . l7 60-MHz NMR spectra of 2-Naphthaldehyde (NapCHO), 2-Naphthalidene— n-butyl amine (NapBI), 2- -Naphthalidene- n-butylammonium ion (NapBIH+ ) and Z-Naphthalidene-n- butyldeteroammonium ion (NapBID+ ). . . . . . . . .19 60- -MHz NMR spectra of 9-Anthraldehyde (AnCHO), 9-Anthralidene- -n- butylamine (AnBI), 9- Anthralidene-n-butylammonium ion (AnBIH+ ). . . . .21 Raman spectra of Benzaldehyde (BCHO), N-Benzylidene-n-butylamine (BnBI), N- Benzylidene-n-butylammonium ion (BnBIH ) ’Vi- FIGURE PAGE and N-Benzylidene-n-butyl-deuteroammonium ion (BnBID ) in methylene chloride. . . . . . . . 27 8 Raman spectra of N-Benzylidene-n-butylamine (BnBI) N-Benzylidene-n-butylammonium ion (BnBIH+) and N—Benzylidene-n-butyldeutero- ammonium ion (BnBID ) in chloroform. . . . . . . .29 9 Infrared spectra of N-Benzylidene-n- butylamine (BnBI), N-Benzylidene-n- butylammonium ion (BnBIH ) and N- Benzylidene-n-buty1deuteroammonium ion (BnBID+) in chloroform. . . . . . . . . . . . . . 31 10 Raman spectra of 2-Naphtha1dehyde (NapCHO) and Z-Naphthalidene-n-butylamine (NapBI) in methylene chloride. . . . . . . . . . . . . . .39 ll Raman spectra of 2-Naphthalidene-n- butylamine (NapBI), 2-Naphthalidene-n- butylammonium ion (NapBIH+) and 2- Naphthalidene-n-butyldeuteroammonium ion (NapBID+) in methelene chloride. . . . . . . . . .41 12 Raman spectra of 2-Naphthalidene-n- butylamine (NapBI), 2-Naphthalidene-n- butylammonium ion (NapBIHI) and 2- Naphthalidene-n-butyl deuteroammonium ion (NapBID+) chloroform solutions. . . . . . . . 43 13 Infrared spectra of 2-Naphtha1idene-n- butylamine (NapBI), 2-Naphthalide-n- butylammonium ion (NapBIH+) and 2- Naphthalidene-n-butyl deuteroammonium ion (NapBID+) chloroform solutions. . . . . . . . 45 14 Raman spectra of 9-Anthra1dehyde (AnCHO) and 9-Anthra1idene-n-butylamine (AnBI) in methylene chloride solutions. . . . . . . . . .51 15 Raman spectra of 9-Anthralidene-n-buty1— ammonium ion (AnBIH+) and 9-Anthralidene- butyldeuteroammonium ion (AnBID ) in methylene chloride solutions. . . . . . . . . . . 53 16 Raman spectra of 9-Anthralidene-n-butylamine (AnBI)4 9-Anthra1idene-n-butylammonium ion (AnBIH ) and 9-Anthralidene-n-butyldeutero- ammonium ion (AnBID+) in chloroform. . . . . . . .55 -vii- FIGURE 17 18 19 20 21 PAGE Infrared spectra of 9-Anthralidene-n- butylamine (AnBI), 9-Anthra1idene-n- butylammonium ion (AnBIH+ ) and 9- Anthralidene-n-butyldeuteroammonium ion (AnBID+ ) in chloroform. . . . . . . . . . . . . . 57 Raman spectrum of Benzophenone (b0) in ChlorOfom. O O O O O O I O O O I O I I O O O O O 62 Raman spectrum of Benzophenone Schiff's base (bSb), its protonated form (bSbH+ ) and its deuterated form (bSbD+ ) in chloroform. . . . . . . . . . . . . . . . . . . . 62 Plot of VC=O(OOO) , vc=N(Dl:lEl) and VC=N(. O.) stretching mode for unsaturated aldehydes versus the number of double bonds in the particular compound. . . . . . . . . . . .82 Plot of vC=O(OOO) , VC=N(D CID ) , VC=NH (0..) and VC=ND(A AA) stretching mode for aromatic aldehydes and imines versus the number of double bonds in the particular compound. . . . . . . . . . . . . . . . . . . . .84 -viii- CHAPTER I INTRODUCTION The suggestion that the chromophore, retinal, is covalently associated with the protein Opsin by a protonated Schiff's base linkage to form the photosensitive pigment rhodopsin (Figure 1a), has stimulated considerable spectroscopic work on the properties of free Schiff bases of retinal and of its protonated form. Because of the importance of the configuration of the Schiff's base in this conversion, Raman spectroscopy has been used extensively to monitor changes in the C=N stretching frequencies during the rhodopsin Photocycle. A frequency change from 1620 cm.1 for the C=N stretch in the non- l protonated species to a frequency of 1655 cm- for the 1 for the deuterated form protonated form and to 1630 cm- has been observed (see, for example, Ottolenghi, 1980; Marcus gt 31., 1979; and Aton 33 31., 1980). Recent work by Ward 93 31. (1983), modeling interac- tions between the carbonyl group of heme a and an amino donor group, show that the metalloporphyrin Schiff's bases (see Figure 1d) which results upon protonation have unusual spectra properties. The C=N stretching frequency -1- Figure 1. Rhodopsin. BacteriorhodOpsin br570, all trans- retinal-+opsin. Bacteriorhodopsin br603, all trans- 3-dehydro retinal-+0psin. Nickel (II) formylvinylporphyrin. 18 1b u3c cu3 °"3 °"3 1d °5"11 / L X=0 M=NI 2,X=N3u 1 X=NHBu + 4.X=NDBu H x/ °s"11 Figute1 -4- for the Schiff's base appears at 1639 cm—1, upon protonation this frequency shifts to 1650 cm.1 and, if the proton is replaced by a deuteron, the stretching vibration is observed at 1640 cm'l. In both cases the observed Raman frequencies corres- ponding to the protonated and deuterated Schiff's base are difficult to understand on intuitive grounds, since, in general, it is expected on the basis of a simple mass effect that protonation will decrease the C=N stretching frequency. Moreover, these C=N frequency changes are not consistent with changes in the nature of the groups on the Schiff's bases. For example, the C=N stretching frequency is higher in the metalloporphyrin Schiff's base, 1639 cm—1, than in the unpretonated retinal Schiff's base, 1620 cm—1, even though the resonance system is more extended and the reduced mass is higher in the former system than in the latter. In the case of visual pigments and their model compounds, the frequency changes which occur for the C—N bond upon protonation and deuteration have been discussed by Marcus 33 33., (1979). They suggested that the interaction of the Schiff's base C=N bond with the N-H bending mode, in the protonated case, contributes significantly to the increase in the frequency of the C=N stretching mode. Support for this model was claimed from the fact that these frequency changes cannot be attributed to a simple reduced mass effect because substitution of the -4- for the Schiff's base appears at 1639 cm-1, upon protonation this frequency shifts to 1650 cm.1 and, if the proton is replaced by a deuteron, the stretching vibration is observed at 1640 cm’l. In both cases the observed Raman frequencies corres- ponding to the protonated and deuterated Schiff's base are difficult to understand on intuitive grounds, since, in general, it is expected on the basis of a simple mass effect that protonation will decrease the C=N stretching frequency. Moreover, these C=N frequency changes are not consistent with changes in the nature of the groups on the Schiff's bases. For example, the C=N stretching frequency is higher in the metalloporphyrin Schiff's base, 1639 cm-1 , than in the unpretonated retinal Schiff's base, 1620 cm-1, even though the resonance system is more extended and the reduced mass is higher in the former system than in the latter. In the case of visual pigments and their model compounds, the frequency changes which occur for the C-N bond upon protonation and deuteration have been discussed by Marcus 3; 33., (1979). They suggested that the interaction of the Schiff's base C:N bond with the N-H bending mode, in the protonated case, contributes significantly to the increase in the frequency of the C=N stretching mode. Support for this model was claimed from the fact that these frequency changes cannot be attributed to a simple reduced mass effect because substitution of the -5- proton by a deuteron decreases the stretching frequency by 25 cm.1 while N15 enrichment shifts this mode by only 13 cm-l. Aton 33 33., (1980) tested this proposal by carrying out calculations on a hypothetical triatomic molecule, C=N-H. Their results showed that by allowing the C=N stretching frequency to interact with the N-H bending mode, they could produce an increase in the C=N vibrational frequency. On the other hand, Massing 33 33., (1982) suggested another possibility for the increase in the C=N stretching frequency upon protonation which involves mixing between the C=N stretch and an adjacent C-C stretch. At the same time, there are other factors which affect the characteris- tic group frequency. Woffe (1975), pointed out that the characteristic carbonyl group frequency depends, in general, on steric effects, reduced mass, conjugative effects, electron delocalization, on the electron donating and electron withdrawing ability of the substituents. Perjessy (1973) indicates that transmission of polar effects due to the CH=CH group also effect the C=O stretching frequency. Seth-Paul (1981) discussed the dependence of this group frequency on the 6CCOC angle. In general, it is known that there is a decrease in the C=O force constant with increasing polarity of the carbonyl group. Thus, when a halogen atom is introduced into the methyl group of acetaldehyde or acetone the carbonyl bond becomes less polar and the C=O stretching -6- frequency shifts to higher values. This behavior was attributed by Bra132 33 33., (1961) to a variation of the effective electronegativity of the carbonyl carbon atom. In addition, Besnainau 33 33., (1966) showed that halogen substitution on similar nitrile compounds produces the same behavior. Furthermore, a hyperconjugation effect was discussed by Howell (1976) and Christen 33 33., (1982), as the main factor in the variation in bond distance of methyleimine halogen derivative. To examine the frequency changes in the imine bond which occur upon going from an unsaturated substituent to an aromatic substituent, as well as to study the possible analogy that exists between the effect of protonation and deuteration of the C=N bond in metalloporphyrin Schiff's bases with respect to the retinal Schiff's bases, nuclear magnetic resonance, infrared and Raman spectroscopic studies have been carried out. One, two and three ring aromatic Schiff's bases (Figure 2) and their protonated and deuterated derivatives were studied. With the identification of the C=N stretching frequency in the various compounds, it is possible to establish whether the increase in the C=N frequency mode of the aromatic Schiff's bases relative to the unsaturated Schiff's bases, follows the same trend as that observed for the carbonyl stretching frequency and the nitrile stretching frequency in an analogous series of compounds. These studies provide Figure 2. a. b. c. d. e. f. g. h. n-benzylidene-n-butylamine. n-benzylidene-n-butylammonium ion. 2-naphtha1idene-n-butylamine. 2-naphthalidene-n-butylammonium ion. 9-anthra1idene-n-butylamine. 9-anthralidene-n-butylammonium ion. benzophenilidene-n-butylamine. benzophenilidene-n-butylammonium ion. H” Ham c an \c/ .. V O W c E. >u d H 9 H‘ C/ / N N : O __ C C 00 . "5.0.0.. -9.- information on the question of whether the increase in the =N stretching frequency in metalloporphyrin Schiff's bases, which occurs upon protonation and deuteration, is an isolated case or can be generalized as a common characteristic of aromatic Schiff's bases. Furthermore, the identification of the N-H and N-D bending modes will provide information that can be used in future work to test the hypothesis that the interaction between the C=N stretching vibration and the N-H or N-D bending modes is responsible for the observed increase in stretching frequency of the imine bond upon protonation or deuteration (Aton 33 33., 1980). CHAPTER II EXPERIMENTAL A.1 Sample Pr3paration Benzaldehyde was purified by distillation in vacuum, 2-naphtha1dehyde and 9-anthraldehyde were recrystallized from a methanol-water mixture. Benzophenone and n-butyl- amine were used with no further purification. Methylene chloride and chloroform were distilled in the presence of calcium hydride. N-benzylidene-n—butylamine, 2-naphthali- dene-n-butylamine and 9-anthralidene-n-butylamine were prepared by producing a reaction with 10 m1 of the appropriate aldehyde in a 4 h. reflux with dry benzene containing an excess of n-butylamine (20 m1). Benzene acts as the azeotropic agent which allows for the removal of the water produced by the reaction (Cordes 33 33., (1963) and Layer, (1963)). \ k1 \ *3 k2 c=o +RNH2 .==—-’ HOC-NH .——— c = N-R+H20 (1) / k-1 I k-2 / Lyophilization yields pure Schiff's bases (Ward 33 33., 1983). After the reaction was completed, the excess n-butylamine and the benzene were removed in a rotavapor -10... -11- system. N-benzylidene-n-butylamine was purified by distillation in a vacuum, while 2-naphthalidene-n- butylamine and 9-anthra1idene-n-butylamine were recrystal- lized in a mixture of methylene chloride and petroleum ether. Since aromatic ketones react with amines more slowly than aromatic aldehydes, aluminum chloride was used as a Lewis acid, thus making the reaction possible. Benzophenone Schiff's base was used without further purification. A.2 U.V. Measurements and Results In order to verify the formation of the imines, ultraviolet absorption spectroscopic measurements of approximately 1 X10”4 M solutions in methylene chloride or chloroform were carried out with a Perkin Elmer Lambda 5, UV/Vis spectrophotometer. Table I shows the blue shift relative to the free carbonyl species upon Schiff's base formation (El-Aasser 33 33., 1971). Table I. lmax(nm) of Aldehydes and Schiff's bases ArCHO ArCH=NBu ArCH=NBu ArCH-NDBu C6H5 248 247 278 277 C10H8 252 251 275 275 265 260 270 -—— -12- Protonated and deuterated Schiff's bases were prepared by adding equivalent amounts of dry HCl(g) or DCl to (g) 0.25 M of imine solutions in methylene chloride or chloroform as solvent. Solutions of approximately 1 ><10_4 M were used to verify the red shift of the n-*n* transition in the U.V. region (Santerre 33 33., 1958) due to the presence of protonated or deuterated Schiff's bases. (See Table I and Figure 3). However, in some cases, the n-+n* transition for aromatic aldehydes, benzaldehyde and 2-naphthaldehyde and the corresponding aromatic Schiff's bases cannot be differentiated. Therefore, another Spectroscopic technique is required in order to establish the formation of the Schiff's bases. A.3 NMR Measurements and Results Nuclear magnetic resonance spectroscopy is a very good technique for identifying aldimines Schiff's bases, since the proton attached to the carbon in the imine bond has a characteristic environment (Parry 33 33., 1970). In addition, protonated Schiff's bases can be observed due to the NH proton interactions. The nitrogen proton (NH) may undergo a rapid, intermediate or slow rate exchange (Silverstein 33 33., 1981). In the case of rapid exchange, the proton is decoupled from the N atom and from adjacent protons. Therefore, the CH protons will not be split by the NH proton. The same observation applies when the NH _13_. Figure 3. U.V. spectra of Benzaldehyde ( ). N-Benzylidene-n-butylamine (-- -—r -—-I. N-Benzylidene-n-butylammonium ion (—-'--*f-). and N-Benzylidene-n-butyldeuteroammonium ion ( ------ ) in chloroform. _14- r 16 *- 0.8 0“! ‘FNAFNAM 000”” .a\ | O/ I oucaatoon< Figure 3 -15- proton undergoes an intermediate rate exchange, since the NH proton is only partially decoupled. However, when the exchange rate is slow, the coupling of the NH proton with adjacent CH protons can be observed. Therefore, the chemical shift and the splitting pattern of the protons can be used to detect the presence of unprotonated and protonated Schiff's bases. Aldehydes and imines were prepared at a concentration of 0.1 M in deuterated chloroform. Protonated and deutera- ted forms were obtained by adding equivalent amounts of dry HCl(g) and DCl(g), respectively. NMR spectra were recorded on a Varian T60 NMR spectrometer at a 0.1 RF power level, at a spectrum amplitude of 10 and at a spinning rate of 40 rps. Figures 4 through 6 show the NMR spectra of n-benzylidene-n-butylamine, n-naphthalidene—n-butylamine, n-anthracylidene-n-butylamine, its protonated forms, and its carbonyl analogs. Table II contains data of the Ha and aCH2 protons, with assignments based on those of Sharma 33 33., (1973) and Parry 33 33., (1970). The change in the chemical shift of the Ha proton indicates the formation of the aromatic Schiff's base from the corresponding aldehyde. The results also indicate that, when the Schiff's base is protonated, the splittings of the Ha proton into a doublet and of the aCH2 protons into quartets are due to the Hb proton present on the imine nitrogen. On the other hand, in the deuterated solution -16- ADVQEI/ .\mmwo .>Hw>fluommmmn nu II m-a-mmo\\m mm m m m o zno\\ m u .o o\\ m o I "/ m-s-mmo\. .11 mm mm .A oncmv :oa Esficoaam ioumumpawusnICImcmpwkucmmlz paw A+mHmcmv cod Eda:OEEmHMusQ|:|mcwpwa>Ncmmlz .-Hmcm- mcflsm Hausnucumcmeflasucmmuz .-omom- messweamucmm mo muuommm mzz “males .3 musmflm -17- T. 3...»:- .8 :28 ozou -18- in can A Hausnlclmcmpfi m m o m a n / \ . Hm>fluow mmu anIII m-s-mmo \\\ 9 mm \\m$oa0 \\WEOHU zno . ouo/ m-s-mmu \ / mm mm .A+QHmmmz- cow EDMCOEEmououwpawusnicumcmpwHmnusmmz mHmmmz- :ofi ESHCOEEMH>DDQICImcmpHHMSDSQMZIN .AHmmozv mcflam wmnunmmzim .Aomommzv mpxnmpamnunmm21N «0 manommm mzz NmZIom .m Gunman -19.. m 2:: :- I. N M v m o h a a 9— fi d -I 1 q 1 —I q a «sub +a=snz a: I 2.323. a «.8 o 020:0: uc_¢ -20- mcHEmeusnic OH ¢H om m o A a /// o.\\ . Hw>wuom mom zn m-s-mmo\\\. e III or OH «H ed «a o m o ZHU . OHU .-+mHmaD5QICImcmpflH>NGmmlz .AHmcmv mcHEmHhusnlciwcmpwkucwmtz .Aomom- mp>£wpamucmm mo muuowmm cmEmm .h musmflm -27- 62! Oltl 1121 688! 268! Bit! 029! l r‘: 865! £59! ::::: 320! 991.. 99 £61! '22! till 508! 908! ISSI 892! lit! 22’! s zn 19." + BnIID lg [usuuu] new“ A (cu-1) -28- .EH0mouoHno ca A+QHmcmv cow ESACOEEmoumusmpawusnlc ocmpflawucmmiz paw A+mHmcmv cow ESHGOEEmawusn Icimcmpflamncmmiz .AHmcm- wcHEmH>DDQICIme©fiaxncmmiz mo muuommm cmemm .m musmflm -29- 1100 l;gsuo;u| 1400 1300 1200 1100 1000 900 A (cm'l) 1500 1000 Figure 8 -30- Figure 9. Infrared spectra of N-Benzylidene-n-butylamine (BnBI), N-Benzylidene-n-butylammonium ion (BnBIH+) and N-Benzylidene-n-butyldeutero— ammonium ion (BnBID ) in chloroform. IntOISIt’ -32... same Schiff's base in chloroform solutions. The frequency assignments for the Schiff's bases and derivatives are shown in Table III. The work of Zwarich 33 33., (1971) on benzaldehyde provided the main assignments for the ring and related vibrational motion of the imines. Thus, the band at 1203 cm-1 is assigned to the vibrational mode between the aldehyde group and the benzyl group in CGHS-CHO. This frequency is absent from.the Raman spectra of the Schiff's base, in methylene chloride solutions a new band appears at 1221 cm-1, being replaced by a band at 1228 cm"1 and at 1224 cm'1 upon protonation and deuteration, respectively. Therefore, this frequency motion may be 8 0 assigned as (C6H5CH=NR), (C6H5CH=NHR) and (C6H CH=NDR). 5 The same observations can be made for the Raman and I.R. spectra of Schiff's base on chloroform solutions, but in this case there is some overlap between a solvent band and the CGHSCH=NR band. Upon protonation of the Schiff's base, the N-H bending motion is assigned to 1423 cm"1 in Raman and to 1418 cm"1 in the I.R. because in the unprotonated or in the deuterated spectra this band is absent. In addition, it is near the N-H bending mode region observed for protonated all-trans retinal Schiff bases by Massing 33 33., (1982) and Aton 33 33., (1980). This band cannot be observed clearly in methylene chloride solutions due to overlap with the solvent band. In a similar manner, the I.R. band at 1 1121 cm- in deuterated Schiff's bases was assigned to the -33- .mmscflucoo HHH magma mcwpcmn 02> smaaa mEONHH 3>H~HH 3NNHH 3vHHH 3vmoa Dad? smooa 3mmoa soboa 3mhoa BVFQH :flmno 010? mmoa 3>mmoa 3000a 3mm0H zmmoa 3000a 3cm0H mma> Samoa Emmoa Benoa Emmoa ammoa Emmoa Samoa Emmoa Emmoa Emmoa ENNOH NH: mmooa Emma mmooa Emma mmooa Booed mmooa wmooa mmooa mmooa moooa mmooa samba samba sewhm camno 3Emvm zfimvm sfimqm mamow Emvm Eomm 305w Hp Smmm Emma mvmm amen mm) Save Save Emvo mEomo mm» ammo ammo some CMEQM “H CMEMNH MH Gag MH GMEMM Ewan“ Cflfimm 55mm Gmfimm NH Naommo mammmo musm unmacmfimg maomo\mHmcm Maw-03135 maomohmcm \mHmcm \mHmcm \Hmcm «mam mac-635m .mpwHoHso onwaanuwa pcm EHOMOHoHno ca A oncmv cow Esflcosfim oumunmpahunnicimcmpflahnnonic can A+mHmcmv new EaACOEEmHMD:QICImcmpHH>N:mQI: .AHmcmv ocfiEmahupniciwcmpwHmucmnic How mmflocmsvoum pwumumcH can enema .HHH manna -34- .mmscHDCOU HHH manna nmflp mamefl sowed mowed 3~m¢H mmvva 3cmva 3HmvH sflmea 3mmva smmva sowed saved sowed 3>ovva 3>ovva ochecmh muzp smmva Emacs smmva unm>aom ammvfl smmva swmva momea mpwnmpam mo 3mmma 3vmma mags“ mu> 3>vsma zsomma 3>VAMH zeomma 3>msmfl msssma 3>mema s>msma 3>msma sauna sawma sound sammfl 3mvma sovma gamma zmmma 3mmmH 3¢mma svmma 3Hmma m> adama smoma 3~Hmfl smoma soama sonH 3>oama 3>HHmH 3>Hama 3>oama onmH amHmH smoma zooma seema smoma 8H; zqmmfl 3mm~H somma 3mm~H 3mmma zomma zvaH 3vm~a 3mm~H szNH seams ucm>aom ENNNH smmma mmmmfl -muznoue-> ECNNH gamma gamma smmma m>m-~ mEONNH zsvmmfl gamma mamma m>HmHH -omouo-> mmoma meoma svaH maemaa smmHH svaH no» 3moHH emmHH sosHH smoHH shoaa sosHH amoaa smoafl sosaa smoaa zooHH samaa 3mmHH omHH mmaa somafl msmHH somaa cmsmm .mH cmsmm mH enema mH cmsmm 888mm enema enema amemm mH «Hommo mammmo mung unmscmflmme maoeo\mHmcm maomomemcm maomo\Hmcm \mHmcm \mHmcm \Hmcm Hmcm mammo\omcm .cmscfiucoo HHH magma -34- .mwscwucou HHH wanna nmap mamva gamed momva 3~mvH mqua gamed samea gamed 3mmva A smmea sowed soewa zoeea 3>ovva 3>ovva mcflocmn muzp ammea smaqa smmva unm>Hom smmvfl smmva smwea momea wasnmoflm mu gamma 3vmmH mafia“ mo> apesma zsomma 3>¢sma zeomma s>mhma massma 3>msma s>mnma 3>msma swama 3HmMH sovma samma amend seems gamma gamma 3mmma quMH svaH gamma mp 3HHMH zaOMH smama swama zoama onMH 3>oamH 3>HHmH 3>HHMH 3>OHMH onmH smama zooms szmH zooms amend 8H> squH 3mm~a 3¢m~a 3mmma 3mmNH gamma semNH zvaH szNH anama gamma ucm>flom gamma gamma mamma -mnzuoue-> gamma EONNH smmmfl ammma m>m~ma msoNNH seemma gamma mamma m>H~HH -omo-e-a mmoma mvoma avmaa maemaa smmHH avmaa nm> smeaa ammHH sosHH smoHH shoaa gonad amoHH smoaa gonna smmaa goofla semaa 3mmHH mmHH mmHH somaa msmaa somaa swam”- E :28”- fi cmsmm M: 5.5- :msmm amas- cmefl- 58$- 4: maommo «Hommo mung ucmscmumma maomo\mHmcm maomomemcm maomomecm \mHmcm \mHmcm \Hmcm Hmam mammoxomom .QODCHHGOU HHH OHQMB -35- .xmm-s hum-w u E oxmmsa H 3 .5258" E . mconum 85..”me u m:- .mcouum u m .mcouum 56> u 9.. onu> mocha moos- cowumcwneoo 3mmma 35mma zuo> momma mmmoa momma mmsma moved mmvofl m>oooa m>ommH m>mvoH m>mvoa mm> Hood mmmmfl mood momma mmooa mooma m>HooH m>~ooH m>~oma wooed mmmma moooa mm> somma zomma 3~mmH momma summa swama 34mma gamma nmaa sewed 3mmvH 3mmva semvfl 3mmea smmva smmva smmva gamed somva sawed sowed sawed sowed 3nmva g m H «EM—EM.“ Mm H 3.65“ m H Human“ EMS CMEMM CM; CMEMNH m H Naommo «Hommo «use unmeemflmmc maomo\mHmcm maomo\mHmnm maomo\Hmcm \mHmcm \mHmcm \gmcm Hmdm maomoxomom .pmscHDGOU HHH mHQMB -35- N-D bending mode. However, a band at 1237 cm.1 in the I.R. spectra and at 1243 cm-1 in the Raman spectra behave in the same way. However, for br and br603, the difference 570 between the frequency of the CNH bending and the CND bending is 370 cm“1 (Massing 35 33., 1982). Therefore, it appears that the former frequency and not the latter can be assigned as the N-D bending mode. Another important change occurs in the band at 1696 cm"1 assigned to the C=O stretching frequency in benzaldehyde. This band, upon formation of the imine, 1 is shifted to 1648 cm’ and is assigned to the C=N stretching frequency. Upon protonation and deuteration this frequency mode shifts to 1680 cm-1 and to 1660 cm-1, respectively. This is in agreement with the previous observed increase in the C=N stretching frequency in protonated and deuterated Schiff's bases (Aton 33 33., 1980; Marcus 33 33., 1979 and Ward 33 33., 1981). It is known that the Raman intensity of certain molecular vibrationS' depends on the conjugation. Schmid 33 33., (1977) investigated the Raman intensity changes of the V8 mode (in compounds of the type CGHSCOX) with changes in the electron withdrawing character of the group X, and indicate that an increase in the V8 mode intensity is related to an increase in the electron withdrawing character of the group X. Also, Schmid 33 33., (1983), investigated the Raman intensity of the phenyl v mode 8 changes with the angle of twist in biphenyls. Therefore, -37- it can be assumed that for phenylimine the intensity of the v8 mode is indicative of the extent of conjugation. Therefore, it is possible to deduce that protonation and deuteration of phenyl Schiff's base changes to some extent the state of conjugation between the imine group and the ring. Since there is a relative intensity variation of the v8 frequency mode with respect to the C=N frequency mode. A.3 2-N3phtha1idene-n-butylamine and Derivatives 2-Naphthalidene-n-butylamine and derivatives were prepared as described in Chapter II. The Raman spectra were obtained with a Aex==647.1 nm and after an irradiation period of 3 hours at a power of 500—600 mw. The spectral slit width used was 3 cm.1 resolution, the range 1 Xl.04 count/sec and the PMT voltage was 1860 v. The other conditions were the same as in N-benzylidene-n-butylamine. Figures 10 through 13 show the Raman and infrared spectra of the corresponding Schiff bases in methylene chloride and chloroform respectively. The frequency assignments were made based on the work of Sharma 33 33., (1974) for a and B naphthaldehydes. Other bands were assigned by comparing with N-benzylidene derivatives. Table IV contains the more probable assignments for the observed vibrational modes. As expected, the greatest frequency changes were observed .meenoaeo memassuoe sh -Hmnnz- ocflEmeusnlcuocmpflHmsusmmzim paw .omummzv mpasmpamnunQMZIm mo manommm cmewm .eH enemas -39- 020! [20! 5901 $51! 091! 01!! 01! “Z 902 "n: '6 tin—$- '96: 00’! Elf! 28'! "N £99! 0111 g 115! .3 ‘3 s U a: [£91 06298?! :09; 0‘89! 5i 099 I: 359! 96“": 1 "won" I run; 1200 1000 1100 1700 1000 1500 1400 1300 1800 A (cm-1) FI‘II’O 10 -40- .mpHuoHso mclonumE CH ESHGOEEmoumusmpqusnICI mcmpHHmnusmsz IN pcm A+ mHmamzv :oH .Aa ondnz- coH HCOEEMkusn IGI mcmpHHmzusmsz IN .AHmmmzv mcHEmeusnICI mcmpHHMSDSQMZI IN mo muuowmm cmsmm .HH wusmHm -41- 1201 o 1zot 5901 1 5911 55‘ 9511 691 69‘ 611! 6811 58!. 1 21:1 82: 6221 :1: 2’1! 99“ tttt 918! 18st 96 CI 22'! 1111 ott1 3 fl 0 z 3091 our 5291—: -__===_- ' : £191 £59 [annual «may 1000 1500 1400 1300 1200 1100 1000 170 0 A (In-'1) Figure 11 -42- .mcoHusHOm Eu0mouoHno A+0Hmmmzv :oH EchoEEmonmpswp HmusnIcImcprHmzunm82I~ cam A+mHmmmzv :OH ESHGOEEmepsn IalmcmpHHmnunmm2I~ .AHmmmz- wcHEmeusnICImcmpHHMSDSQMZIN mo muuommm cmfimm .NH muzmHm -43- 610 2001 1:11 2011 81! 1121 09:1 81:1 08:1 - 568! 901 - 0111 tit! 8911 0191 + _ a 2 '3. . C 2 z 0091 A (Au—L 0291 fTrT‘ 333333,,:) 8991 TTTT‘] 5191 [usuuul “may 1000 1500 1400 1300 1200 1100 1000 1700 0 (0111’!) Figure 12 -44- Figure 13. Infrared spectra of 2-Naphtha1idene-n-buty1 amine (NapBI), 2-Naphthalide-n-butylammonium ion (NapBIH+) and 2-Naphthalidene-n-butyl deuteroammonium ion (NapBID+) chloroform solutions. —45_ _ n «no a——— «sun sou. as»— gown mama ano— ecc— m D. C I" 1400 1200 1000 300 600 1 600 1800 A (cm'l) Figure13 . 6 4 _ .mmchuaoo >H magma nuances mo> zemHA zemHH 3A~HH smfiaa mchcmn 012? ENHHH ammoa defleemh mo> 3H~oH somoa somoa zoNOH sawed soNOH gadoa 3mAOH Emma amen seem emsm mchcmn no? 30mm defiesmh mo> 30mm 30mm 305m coHuHoume Hmummem mchcmn mo) Eoom mEomm mEmmm mehcemh mo> namam mamam nsmam same ammo ammo ammo seem COHHHODme Hmumexm CMEMM m H CMEMM M H GMEMM m H C MEwm Cmfimm emwumwmwm «Hommo\+aammmz «Hommo\+mHmmnz Naommo\Hmmnz maommo «Hemmo wannnoun \+onmez . \+mHmmmz I‘ll. .mw>Hum>Huwp paw wcHEmHmusnIcImcmpHHmcunmmclm Mo mmHoamsUwuw pmumumcH paw Gmfimm 3mmHH somaa smHHH ammoa smaoa EONOH zomoH 30mm seam 30mm mammm macaw 30mm :mgmm enema mH «Hommo «Hommo\omomez \Hmmnz .>H OHQMB -47- .mmscHucou >H mHnma noumuun v-09 Amaommo- ucm>H0m muz> noumuum ouo> noumuun 0:09 soumnun ciu> soumuum oto> scannounas Hmumamxm Amaomo- ucw>aom meacsmn mo> meaeemn mo> soaununa> mo mopoz wHQMQOHm sveva mmea >oova smmma gamma 3vnma smmma Hema msaema omma smmma sawma saama somaa msomaa 3moaa 3ooaa COEmm mH m m ao mo\+oammmz savea 3>ovea omea mava smmma smmma smema 3coma somma svema 3ovma oema msoema emma mammma >amma smmaa nsomaa 3mmaa zmoaa cesem ma N N am mo\+mHmmez sovva 3mmva smmma smema ansma 3>oema somma smoma smoma 3amma smsaa 3ooaa andm ma m m ao moxammnz 3N¢vH EMNvH 3vOVH mGQMH EmBMH BthH EmNNH mEmmHH 3mmHH CMEMM N N ao mo +oamamz 3N¢¢H MNvH hHwH wmwma Eonma 3>whNH EmNNH EmmHH 3®mHH amemm N N ao mo \+mammez savva mmvea sovea smmea mmmea nvoea gamma n>mmma svsma nmnma enema Enema zooma zeoma smmma 3ma~a zomma smeaa moeaa soeaa 3mmaa semaa 3omaa Ema-HM“ EMA-“mm NH Naommo maommo\omomnz \ammnz .omscausou >a manna _ 8 4 _ GNU? ZN noumuun ouo> noumnun ouo> soumnum ouo> soumuum 010? noumnun ouo> soaumuna> mo mono: maamnoun mmmoH mmvwa mONoH mONoH 3000H ENmmH 3>OHmH 3momH EOBVH Emmwa :mewm mH NHUNmU\+DHmmz nmeoa nmmma nmmoa momma sooma ammma 3aama moma msanva saova EMA-Hm“ mH Naommo\+mammez n>meea n>oeoa momma somoa zoooa smmma 3aama zooma msmoea eoeva enema ma Naommoxammez m>mm®H moNoH 3mmmH 3>ommH thvH cmemm N N ao mo +oammnz mmmoa mmN®H 3mmmH 3>mme ENNVH C050“ N N ao mu \+mammmz n>emoa momma m>vvoa n>oMma m>amma nmmoa smooa smmma smmma smema enema enema 3>aama soama 3mmaa echea noova sooea Cg CMEMM m H Naommo Naommo\omomez \Hmmmz .pmscHucoo >H mHnma -49- for the C=N stretching frequency upon protonation and deuteration. Thus, for example, there was a change from 1 (Schiff's base) to 1673 cm"1 1644 cm- (protonated Schiff's base) and to 1653 cm-1 (deuterated Schiff's base) respectively. In addition, some small changes on the C-C stretching frequency of the ring were observed. These, toqether with variations in the relative intensities of the bands at 1630 cm_1 with respect to the C=N stretching frequency, may indicate, as in N-benzylidene-n- butylamine derivatives, a change in the state of conjuga- tion between the aromatic system and the C=N group upon protonation of the Schiff's base. A.4 9-Anthra1idene-n—butylamine and Derivatives 9-Anthralidene-n-butylamine and derivatives were prepared as described in Chapter II. The Raman spectra were obtained with 1ex==647.1 nm with a period of irradiation of 5 hours at a power of 500-600 mw. The other conditions were the same as in 2-naphtha1idene-n- butylamine. Figures 14 through 17 show the Raman and infrared spectra of the imine and its derivative in methylene chloride and chloroform respectively. The frequency assignments were based on the work of Ohta 33 33., (1977) related to vibronic coupling studies on anthracene. Table V presents the more probable assignments for some -50- .mcoHusHOm opHuoch mcmHmnqu :H AHmcdv mCHEMHmusnIcImcmpHHounuchm paw Aomucmv moanmpHmunucH5nochHamunDC< Im paw A+mHmcHSQ IcImampHHmunucmim .AHmcdv mcHEmHNDSQICImchHHmusquIm mo muuommm cmemm .ea mnsmam -55- :20 0501 *2 3 B ‘ 6017 1111 at - 6121 09: 18:1 2181 ii" :21 008! £091 99” In” 5251 VSSI-—-==:* 291 3891 £29! 0991 0101 411511011" 11011133 1000 1500 1400 ‘1300 1200 1100 1000 1700 A (cm’l) Figurolfi -56- Figure 17. Infrared spectra of 9-Anthralidene-n-butylamine (AnBI), 9-Anthra1idene—n-butylammonium ion (AnBIH+) and 9-Anthralidene-n-butyldeutero- ammonium ion (AnBIDI) in chloroform. -57- ooa mne— Willi Q:— can“ cmLa Imma— llllhlueuand I 32 m a M mNN— ”a N «am— evma MM! mn— can— I mnna v va vaa we a. . em: cmv— NHHV cav— em— mama I an m— mnoa mvm— + w N Am .A .A 0' y gluten, t 900 1400 1200 1000 A (cm'l) 1600 1800 Figural? -58- .mwscHucou > anmB a mu> Emema mema smema smmma 3emma smmma 30mma somma smoma smoma 3moma 3m0ma somaa 3mmaa somaa ssmaa 3msaa smeaa 3mmaa smeaa 3>mmaa 3mnaa somaa sooaa nmmaa 3mmaa 3meaa somaa 3mmaa soeaa somaa soeaa 3meaa az> nseaaa 3maaa soaaa sahoa Eonoa somoa omoa 3Sea 383 nmeoa deansen :09 noon mmaoa 3mmoa nmaOa 3mmoa 3mmoa 3mmoa somoa seen some ammo. mmmm some scam 30am oeaeewn :09 n>oom n>oom n>mmm soon meaeemn mo» some smen seem sewn meaeemn mo> seem oem seem seem awe-mm mH cos-mm NH :05 NH :mEamm ace-mm Haw-5mm cmfimm mH maomo\+aams< maomo\+mam:< mammo\am:< maommo maommo maommo omos< \+oamem \+mamsm \amse .mm>Huw>HHmp paw mCHEmHhusnICIwcmpHHMHnUGMIm mo mmHocmsvaw wwHMHMGH paw cmfimm .> mHnme -59- noumuum nououum nouwuum noumuum 200? DID? 0109 0109 DID? Amaommo- nem>aom nououum 0109 somma mmmma 3emma somma Emmma mmema somma eomma somea somea mmeea amoea 3ooea smema eoema 3oama momma mmmma enema ma maumox+oams< mooH mowed EVNQH EONQH mmmma mwvma EONmH 3vmvH zowva momvH mvovH 3oova EmmMH Eovma 3OHMH 3omNH mmmNH mmmNH Gmfimm mH MHUmU\+mHmc¢ seema mmema semma Eomma somma 3omma smama 3moea 3omea moeea mmaea 3oaea 3omma HMMma smoma Emmma 3omma memma momma :msmm mH maomo\ams< eosma smmma smmma semma memma 3mmma 3mmma somea somea smmea smmea mmoea mmoea seema smema 3>ohma 3mmma mmmma momma saga CNS maommo aommo \+QHmC< \+$Hm¢< Eova EMNQH EmmmH BHNmH 3QQVH EMNvH mOHvH Eqvma EmmNH omNH cmemm N N au mo \amca EvnoH EmNoH momma 3>mNmH 3>mmVH EMNvH m¢ovH 3OvMH 3vaH vaH momma 3ON®H momma 3onH 3mmvH Eovva 3oovH Evmma 3m0ma BomNH mvaH Ememm mH Om0c¢ .pmscHucou > manna -60- of the observed frequencies. The C=N stretching frequency behaves as before, increasing in frequency upon protonation of the Schiff's base. However, the frequency corresponding to the N-H bending mode cannot be assigned since there is a very strong band in the 1400-1404 cm“1 region which may overlap the expected N-H bending frequency. A.5 Benzophenone Schiff's Base and Derivatives Benzophenone Schiff's base and derivatives were prepared as described in Chapter II. The Raman spectra were obtained with the excitation at 647.1 nm and the instrument conditions were the same as 9-anthralidene-n- butylamine. These are shown in Figures 18 and 19. The band observed at approximately 1600 cm.1 can be assigned as the analog to V8 in benzene. The frequency at 1656 cm-1 on benzophenone is characteristic of the C=O stretching 1 1 frequency, while the frequencies at 1618 cm- , 1636 cm- and 1616 cm.1 are assigned to be the C=N stretChing frequency of the unprotonated, protonated and deuterated Schiff's bases respectively. -61- Figure 18. Raman spectra of Benzophenone (bO) in chloroform. Figure 19. Raman spectrum of BenZOphenone Schiff's base (bSb), its protonated form (bSbH+) and its deuterated form (bSbD+) in chloroform. -52- M 600— 960— m onus.” anon O m w b b 3.33... can-n.— onfil Qan— emo— 1700 1575 1700 1550 A (61114) A (0111'!) Figure 19 Figure 18 CHAPTER IV SCHIFF'S BASES A.1 Introduction Schiff's base and protonated Schiff's base vibrational modes have been studied for at least the past three decades. Part of the interest in these species derives from the occurrence in biological systems of Schiff's base linkages, for example, in pyridoxal enzymes (e.g. Witkay and Beiler, 1954) and, more recently, in rhodOpsin (e.g. Aton 33 33., 1980). Perhaps as a result, a systematic investigation of saturated, unsaturated and aromatic Schiff's bases and protonated Schiff's bases has not appeared. Rather most reports deal with compounds specific to the problem at hand. Thus, the C=N stretching frequency for saturated aldimines was assigned by Fabian 33 33., (1956), to the 1665-1674 cm'1 range which was extended by Steele (1964) to the 1665-1680 cm'l. N-(n-propylidene)-n-propy1amine, has an I.R. absorption at 1673 cm-1 (Fabian 33 33., 1956) while the simplest aldimine, methyleneimine, (Botschwina, 1974) has a C=N 1 stretching frequency around 1642 cm-1. The 31 cm- difference in the C=N stretching frequency between these -63- -64- two imines could be due to the fact that for the CHZNH species the C-C=N group structure is not present, whereas in propyleneimine it is. In methyleneimine, upon substitution of the hydrogen at the nitrogen by deuterium, the C=N stretching frequency decreases to 1629 cm.1 and upon N15 substitution this mode shifts to 1627 em’l. Christen 33 33., (1982), observed that when the hydrogens in methyleneimine are substituted by fluorine, the C=N stretching frequency increases to 1740 cm-l, while substitution by chlorine decreases the frequency to 1728 cm-1. Aromatic aldimines of the type C6H5-CH=N-R exhibit a C=N stretch in the 1658-1629 cm”1 region, and in the 1637- 1626 cm-1 range when the R group is substituted by a phenyl group (Fabian, 1956). Witkop 33 33., (1954) in a study of possible pyridoxal modes indicates a 1 1639-1626 cm- (Patai, 1970) range for aromatic Schiff's base models and a 1672-1646 cm.1 range for their salts. A further reduction of this mode to 1640-1610 cm"1 is obtained when the number of substituent phenyl rings increases. In general, these reports show that the region over which the C=N stretching frequency occurs is relatively extensive, from 1600-1680 cmul. This, to some extent, suggests that the C=N stretch can be influenced by motions involving neighboring atoms. Therefore, the Physical and chemical environment of the C=N group, -55- including such factors as the presence of electron donating or electron withdrawing substituents, conjugation effects, resonance effects and hydrogen bonding are the main determinants of the C=N stretching frequency variations. References such as Fabian (1956), Colthup 33 33., (1964) and Patai (1970) can be consulted for more details. A.2 =N Stretching Frquengy in Unsaturated and Aromatic Schiff's Bases The results indicate, as can be seen in Table VI, that the changes in C=N stretching frequency in unsaturated Schiff's bases follow the same trends as the carbonyl stretching frequency in aldehyde analogs. That is, as the number of unsaturated bonds increases, both the carbonyl group and the imine group decrease in their respective stretching frequencies. This behavior has been attributed to the mesomeric effect observed in these kinds of unsaturated bonds (Bratéz 33 33., (1961) and Yanovskaya 33 33., (1973)). Similar changes in frequency can be observed in Table VI when aromatic aldehydes and aromatic Schiff's bases are compared; an increase in the resonance system leads to a decrease in frequency. However, the variation in the C=O stretching frequency is greater than the frequency change of the C=N stretching mode, for example, increasing the resonance system from benzaldehyde to cyt 33+ or cyt 32+ (both porphyrin systems) there is a -66- .moscHucoo H> mHQmB Ama- mema Am- mema ameHEaamusnmemanwrunm Am- mmma amomemoamwsnea Ama- mema Am- eema ameaEaamnsnmemamusnmz Am- emma mmomsmoamnsonz Am- mema Am- mema ambasaamusnmsmamnemm Ama- eoma emomrmoannsmm Amm- omma mmwosoosonso ea: Am- mmma mmeasnamxmei.aneanmnumemwe Am- mmma mamsaumwumenne Am- mema mAmmo-moznmomAmoumo-mmommo Ama- mmma omomAmUImU-mmo Ama- mmma mAmmo-mznmoAmoumo-mmo Ama- omma omomAmoumo-mmo Am- mmma mAmmo-mzumoAmonmo-mmo Ama- omma omomonmommo AmH- mmma nmAmmo-moznmomoAmmu- Ama- mama monommo Amao mema mmzuomm AHIEo- zno> QEOU AHIEo- OHU> QEOU .mGGSOQEoo OHDMEOHM paw meMHDDMmcs mo Nocmsvmum mcHnououum mcHEH can chonhmo .H> manme -67- .xnoa manna uAmmma- ..Hm mm emmEanmm NAomaa- ..Hm mm meanoeoe uAamma- ..Hm mm saunaa uAemma- measeomuomm uAnoma- ..Hm mm obese aAmmaa- ..Hm mm mamme-a.a “33: ..am mm uon>mmn “:3: ..HM mm nanmrmm “:3: ..HM mm roannzme “:3: ..HM mm mommmm -Ammaa- ..Hm mm nmmxm>oemme Am- mama nmmomAmro-IzuomAmrmo- Am- mmma Ama- mama Ama- emma monoImAmmmo- Am- ooma mmuzqummmo- Amm- mmmH +Mm mEounoouwo mmma encamem m msonrooumo Amm- mmma W+mm msonrooumo AHIEO- zuU> QEOU AHIEUV 009 . QEOU .omsnausoo a> manna -68- change in the C=O stretching frequency of 18 and 29 cm-l, respectively, while from benzyleneimine to the cyt 3 analog the difference in the C=N stretching frequency is only 7 cm-l. These observations show that the C=N stretching frequency is relatively invariant to increases in the magnitude of the resonance system. On the other hand, the lower values observed for the C=N stretching frequency in ketimines shows that the axes of the n orbital of the additional phenyl rings are planar with respect to the n orbital of the C=N bond. In this way the presence of an aromatic ring on the carbon increases the extent of conjugation in the system which results in a corresponding decrease in the C=N frequency mode (Patai, 1970). Consistent with the general trends in Table VI, the difference in C=N stretching frequency between the M chromophore (1620 cm-1) and the cyt 3 412 Schiff's base (1639 cm—1) follow the same direction as the trends observed for unsaturated and aromatic Schiff's bases, respectively. Bennainou 33 33., (1966) in a very well detailed study on the mechanical coupling and electronic perturba- tion that can affect the CEN stretching frequency in nitriles, suggested that variations in the CEN stretching frequency between unsaturated and aromatic nitriles are due to different degrees of conjugation. Mechanical coupling of different modes was shown to play a minor role in producing vCEN frequency variations. -69- Since what is called the characteristic C=N frequency is a frequency characteristic of the CCN group rather than of the C=N bond, it is possible to suggest that the varia- tion on the C=N between aromatic and unsaturated Schiff's bases is mainly due to electronic effects. Similar behavior was suggested by Besnainou 33 33., (1966) for the nitrile bond. The study indicates that in methylated and halogenated acetonitrile the inductive effect determines the behavior of the CEN stretching frequency. For example, in halogen substituted acetonitriles the effective electronegativity of the a-carbon increases and then decreases as the number of chloro substituents increases. This behavior allows an increase and a decrease of the CEN stretching frequency, respectively, depending on the number of chloro substituents on acetonitrile. The conjugation effect is operative in conjugated and aromatic nitriles. In order to calculate the CEN force constant, it was assumed that its magnitude was dependent on the n electron structure of the molecules, as well as on the o substitution, since the latter can affect the behavior of the n system. It was found that the two vibrations, VCEN and vCC' provide the major contribution to the frequency observed and that the contribution to the CEN stretching frequency of each of the other vibrations was on the order of only a fraction of a wave number. A similar approach was used by Bratéz (1961) to determine the influence of -70- electronic effects on the C=O stretching frequency. He concluded that the variations in the C=O stretching frequency are mainly vibrational coupling interactions for cyclanones and that they do contribute to some extent to the C=O streching frequency in aldehydes. He also showed that when this vibrational coupling is small, the AVC=O frequency shifts are mainly determined by the effective electronegativity of the carbon and in some cases by conjugation effects. On the other hand, Kamarow 33 33., (1975) proposed that the change in energy for the singlet n+-n* state is greater for compounds of the type ArCHO (where Ar==phenyl, naphthyl, antracene) than for conjugated bond systems of the type H-(CH=CH)nCHO, and suggested that, with the same number of double bonds, the extent of conjugation is greater for unsaturated aldehydes than for aromatic aldehydes. For imines the extent of conjugation between the n orbital leads to an increase or decrease in the characteristic C=N frequency. Therefore, the availability of orbitals with appropriate symmetry on a series of adjacent atoms leads to delocalization through the resulting molecular orbital. As a result the bond lengths increase and the stretching frequency decreases. In other words, the lower C=N stretching frequency observed for unsaturated imines with respect to the C=N stretching frequency observed for the aromatic imines (with the same number of double bonds) indicates that the -71- compatibility between the n orbital of the C=N bond (1 a" for methylene imine) with the n orbitals of the aromatic ring is to some extent smaller than the compatibility between this orbital and the n orbitals of the unsaturated analoqs. Therefore, the extent of conjugation can be expected to be higher for unsaturated imines than for aromatic Schiff's bases with the consequent decrease in the C=N stretching frequency. A.3 C=N Stretching Frequency on Protonated and Deuterated Aromatic Schiff's Bases The experimental results are summarized in Table VII and indicate that upon protonation or deuteration of the aromatic Schiff's bases, an increase in the C-N stretching frequency occurs, which is similar to that observed upon protonation of the unsaturated Schiff's bases under the same conditions. This fact in terms of the simple relation between frequency and force constant suggests that the force constant of the C=N stretching mode increases upon protonation or deuteration of the Schiff's bases. On the other hand, the resonance structure of the charged Schiff's bases, i.e., t at C-Ifl 6” ‘\e A, N\- ’- \\. indicate that the frequency of the C=N and therefore, the force constant to decrease. A similar argument was -72- .mmscHucoo HH> manna Ame-ooma Ame-mmma eamnooosm Amomnn- cameo + Amm-mnm Ammomema Amm-mmma Ame-aema amsaumwowomrmoumnmdnnuuaa4 Achmun- CHmmo Aux-moo Amm-omma Aux-mmma Ammomema .+an:aumnmsmuunaa< Ammoomma nemwonmosonro maez A+m- Am-emma Am-emma mameaenamxmsi.aneaumnnmenns A+m- .m m I m I m m Amaommma Am-mema A monUZImo Amonmo- mo mu m m A+m- m AmH-mmma Ama-mmma . A moomozumomouro mo A+m- m m m m Ama-eoma Ama-mmma . o A muomoznmomo A mu- m m um um um 60 GI > So I 9 Eu I > So u 9 EU 0 9 Gnomfio AaI - z AaI or z AaI -mz o Aau -mz o AaI -z o o o .mmmmn m.MMH£om UHHmEOHm cam omumnsummcs omumumusmp pom omumcououo .pmumcouonocs MOM mmHocosvmum 0Hooomonuomomm: can cosmm .HH> manna -73- .mmscHucoo.HH> mHnma AmH-vHHH AmH-mHHH AmH-HNHH Am-ONHH Ae-eea AaIee-AoIzma AmH-mmoH Amm-omoH AmH-mmoH Am-oooH AmH-mooH Am-moma AmH-Hsma Am-omoH AB-ommH AB-NNmH Amm-oema AmH-Nmma Am-mmma Ama-maea Ama-omma Am-mNeH Am-mmma AmH-maea Ama-mmma Am-mNea Am-omma AB-mmma Aa-omma Aa-ooea m an AaIsbomIz > AaIso-mZIo > um IEo-mzno > m \\\ CC ZNU/ m a memo Amm-mmmH A>Hv 6A. @0128 M {Ho Ama-mmma Aaaa- mmeo r m // .\\ \\\ I // Am-mema A o . m- omeao + + Amaomema nAaa- oreo r // \\\\ Z" // Am-eema A o . rm\ mmoao + + o v AmH-mvoH AH- m U m N / \ Z" // AmvovoH A Q m m%\\ mmov + + AB-vNOH mcmhaom HMOoH AB-mmva momlzuo OHEOHMHHU ammoH lab-Zuoum9 nanomeou .omscausoo aa> manna -74- 11 III 11' II. .mm .o co aa> manna on mmuoz Ama-omma Amaomama Aaxo omeo memo / \ Z" 8 \\ 11m m Am-mama Amommma Amomama A+o .+m- m o “H b A :63 Co o/ \nmmo Z" l/m m Ama-maoa Amomoma m o Amavmmma Amaomoma Axa- -m// .\mmmo Z“ Am-emma Amoooma a .//mmmo mmo Aaaaz znofl a- Ama-mmma o uo\\ \ /... e m r o AaaZ 200/ m Ama-omma e ono\\ \\ l/m m r m o Ae>o mmo Amaommma zuo o meme I n a um I um aHIEUvQ z > afllEO- $12 9 aflIEUvaIU 9 AHIEUVWMZNU 9 aHIEOVZNUUm? UCDOQEOU .omscaudoo aa> manna -75- .Ammoa- ..mm_mm cannon .Ammoa- ..mm_mm owmnomam .Ammma- ..mm mm one-s.a .xHo3 mHnam .Aamma- ..Hm mm some .Ammma- ..Hm mm mammnz .Aasmao ..mm mm momma .Aomma- ..mm mm uow>mm p o o c .aa> wages on mmuoz -76- presented before by Blatz 33 33., (1975); Elguero 33 33., (1967) and Goulden (1953). For rhodopsin and analogous Schiff's bases it was assumed by Aton 33 33., (1980) that protonation increases the extent of n-electron delocalization and therefore, the C=N stretching frequency should decrease. But since the observed frequency is greater for the protonated than for the unpronated Schiff's bases, it was suggested by Marcus (1979) and developed in detail by Aton 33 33., (1980), that in the case of unsaturated Schiff's bases, the increase in the C=N stretching frequency is due to the interaction between the C=N stretching frequency at 1624 cm.l and the N-H bending mode at 1250 cm-1. The interaction between these modes was suggested to increase the frequency of the higher mode to the value observed for the C=N stretch in the protonated form. If this is the case, it may also be supposed that aromatic Schiff's base will show a similar behavior. Thus, for example, in N-benzylidene-n- butylamine (compound I), the interaction between the N-H bending mode at 1425 cm.1 and the C=N stretching frequency at 1646 cm-1 would interact to increase the stretching frequency of the later mode to 1680 cm-1. However, at this point, it is necessary to notice that although the C=N and N-H stretching frequencies are substantially different between the retinal Schiff's base analog and the n-benzyl Schiff's base, the difference in stretching frequency between their unprotonated and protonated -77- Schiff's base is practically the same, i.e., 35 cm-l. Therefore, in order to determine whether the stretching- bending interaction model accounts for the frequency changes upon protonation of aromatic Schiff's base, a normal coordination analysis needs to be performed in the future. On the other hand, it is difficult to eXplain some of the C=N stretching frequencies, presented in Table VII, in terms of the bending mode interaction model. For example, the series of compounds from V to VII (which do not have N-H bending mode) present C=N stretching 1, 1658 cm’l, and 1660 cm'l, frequencies of 1658 cm— respectively. These frequencies are, in fact, higher than the C=N stretching frequency (1646 cm-1) for the benzaldehyde Schiff's base analog (compound I). From simple arguments, one would expect that the presence of a ring on the nitrogen would decrease the C=N stretching frequency since an increase in conjugation can be expected (Parry 33 33., 1970). In addition to the above criticism the ketimine derivative prepared from benzophenone and NH3, which contains N-H as a terminal group (compound X, Table VII) has a C=N stretching frequency at 1600 cm"1 (Datin 33 33., 1969), while the ketimine containing a butyl terminal group attached to the nitrogen (compound XI) has a C=N stretching at 1618 cm-1. Similar ketimines, where the terminal group is -CH2CH2CH or C6H5, present 1 C=N stretching frequencies of 1616 cm-1 and 1614 cm- , respectively (Fabian 33 33., 1956). When the n-butyl -78- derivative Schiff's base is protonated, there is a 16 cm-1 increase in the C=N stretching frequency. So, if it is assumed that the N-H bending mode interacts with the C=N stretching frequency and increases the frequency of the latter, one would expect, by a simple mass effect, that the ketimine which contains only the N-H bond as a terminal group will have a higher C=N stretching frequency than the ketimines with alkyl substituents. However, this is not the case, since, as discussed above, the aromatic ketimine derivative from NH3 has a C=N stretching frequency at 1600 cm_l, while the protonated aromatic ketimine from n-butylamine Schiff's base has a C=N stretching frequency at 1636 cm'l. Therefore, at this point, it appears that the interaction between the N-H bending and the C=N stretching frequency cannot account for various of the observed increases in the C=N stretching vibration upon protonation of aromatic Schiff's base. Rather, the protonated Schiff's base case seems to be analogous to the situation which occurs when a proton is brought up to NH to give NHE. The lone pair electrons forming the new N-H bond will not stay unaltered in their sz hybrid orbital, neither will they be equally shared between N and H; they will assume some intermediate distribution (Brown, 1957). Thus, it appears that the possible change in the state of the electron lone pair, as well as the increase in the electronegativity of the nitrogen atom upon protonation of the Schiff's bases -79- play an important role in the CN+ stretching frequency increase relative to the C=N frequency mode. Bond order and bond distance also contribute to the magnitude of the kC=N value. The interplay between these and the increase in the electronegativity of the nitrogen determines the value of the C=N frequency in the Schiff's bases upon protonation or deuteration. For example, in 1 (CH CHCH=NCH(CH3)2 there is a shift of 37 cm- (from 3’2 1667 to 1704 cm-1) upon protonation. At this point with only one double bond, there is n0' strong delocalization effect (no conjugation) which means to some extent that the increase in the electronegativity of the nitrogen controls the change in the C=N stretching frequency and, therefore, the change in frequency is relatively large. In CH3CH=CHCH=NCH(CH3)2 there is only a 7 cm.1 change upon protonation which means that conjugation and electro- negativity effect cancel to a large extent. For retinal a larger shift (approximately 27 cm-l) is observed and Massing 33 33., (1982) indicate that there is no change in the C=N stretching frequency or in the C=N stretching frequency for the addition of a double bond on br570. It can be suggested that the increase in the electronegativity in the nitrogen atom plays an important role in the increase of the C=N stretching frequency. The compounds used for this study (I, II and III in Table VII) behave as if electronegativity effects dominate (i.e. delocalization is small). This is consistent with -80- the NMR data for heme 3 Schiff's base analog in the Ward 33 33., (1983) paper where strong electronegativity effects are observed but small delocalization effects (there is a possibility that the charge delocalizes over the CB=CB double bond on the pyrrole ring but it does not delocalize into the major porphyrin n electron system). The NMR data for the model compounds (see Tables II and Figures 4-6) suggest also that upon protonation or deutera- tion of the Schiff's bases, there is a strong electro- negativity effect as can be deduced from the downfield shift of the Ha and 0ICH2 protons, and that the extent of charge delocalization is not apparently uniform in the ring system. Figure 21 shows that as the number of double bonds increases in the series of protonated aromatic Schiff's bases, the electronegativity contribution effect on the C=N stretching frequency appears to be smaller or the conjugation effect larger. Figure 20 also indicates that the variation on the C=N stretching frequency as a function of the number of double bonds is smaller for unprotonated Schiff's bases than for protonated Schiff's bases; the latter seems to follow a similar trend as the carboxylic group in analog aldehydes. With respect to the decrease on the C=N vibrational mode upon deuteration relative to the C=N mode upon protonation it can be observed in Table VII that it is not constant and appears to -81- Figure 20. Plot of vC=O(OOO) , vc=N(DDD) and vc=§(000) stretching mode for unsaturated aldehydes versus the number of double bonds in the particular compound. -32- A MI“) I 1700 1090 - 0 1080 ,- O 1070 I 1000 A 1050 - 1040 - 1030 .. 1020- DOUbLE BON 08 Figure 20 -83- and vC=NB(AZlA) stretching mode for aromatic aldehydes and imines versus the number of double bonds in the particular compound. -84- u-flaoa am am :8: .132 oom— eso— eco— (14”) V -85- depend to some extent on the magnitude of the aromatic substituent group. On the other hand, a normal coordination analysis to modeling the N-H or N-D model interactions with the C=N stretch has not been performed yet. Until the nature of the C=N stretching increase upon protonation in aromatic Schiff's base with respect to the unprotonated Schiff's base is established, any attempt, at this point, to explain the frequency shifts between the C=N stretching frequency upon deuteration with respect to protonation in terms of bending mode interactions, conjugation effects or inductive effects will not have any firm basis and will only be speculative. However, it should be indicated that the difference in mass between hydrogen and deuterium can contribute to the difference in frequency between the -C=gH and C=QD stretching modes (Marcus 33 33., 1979). It is not clear how much this mass effect can contribute to the difference in frequency of the stretching modes. CHAPTER V SUMMARY AND FUTURE WORK A.1 Summary The C=N, C=NH and C=ND stretching frequency for some aromatic and unsaturated Schiff's bases have been discussed and the corresponding C=N stretching modes assigned by I.R. and Raman spectroscopy and the chemical shift of the Ha and aCH2 protons or protonated Schiff's bases have been determined by NMR. It was shown that the increase in the C=N stretching frequency in aromatic Schiff's bases relative to the C=N stretching mode in unsaturated Schiff's bases follow the same trend that the variation in the carbonyl stretching frequency in the aldehydes or in the nitriles of analogous compounds. Therefore, it appears that the difference in the C=N stretching frequency between the M412 chromophore and the metalloporphyrin Schiff's base (cytochrome 3 analog) is mainly due to electronic effects rather than mechanical coupling. At the same time, the C=N stretching frequency in aromatic Schiff's bases of the kind ArCH=N-R (where Ar==phenyl, naphthyl, antracene) shows a lesser degree of delocalization effects (with an increase in the number -86- -87- of double bond systems) than the carbonyl group stretching mode in the analogous aromatic aldehydes. This fact also applies to the protonated and unprotonated Schiff's base. There is more similarity in the behavior of the conjugation effect between protonated aromatic Schiff's bases and analogous aldehydes than between protonated and unprotonated Schiff's bases. The NMR, I.R. and Raman spectroscopic results have' indicated that upon protonation of the aromatic Schiff's bases, the positive charge on the system is not uniformly distributed in the aromatic system. Rather than this, the large increase in the electronegativity in the nitrogen apparently increases the electron withdrawing character of the imine group and localizes, to some extent, the positive charge. This fact, together with the arguments presented in Chapter IV, indicates that the increase observed in the C=N stretching frequency upon protonation or deuteration of aromatic Schiff's bases cannot be attributed primarily to the coupling between the C=N stretching frequency and the N-H or N-D bending mode. It appears that the interaction between the lone pair electrons on the nitrogen with the hydrogen or deuterium upon N-H or N-D bond formation, with the corresponding increase on the nitrogen's electronegativity, play an important role in increasing the C=N stretching frequency. It was not possible to account for the nature of the deuterium shift that happens when the hydrogen atom on -88- the nitrogen is substituted by a deuteron. However, it is possible to indicate that differences in electronic effects such as electronegativity, inductive effect may play a decisive role in determining the small shift observed. A.2 Future Work The efforts for future experiments and calculations need to be focused on determining a good value for the C=N stretching force constant for unprotonated, protonated and deuterated aromatic Schiff's bases by using the compound presented here as models. However, since the geometry of the model Schiff's base is not known, it may be postulated that upon protonation of the Schiff's base there is an increase in the electronegativity of the nitrogen (Brown, 1957), and an increase in the electron withdrawing character of the C=N group (Ward 33 33., 1983). There is also the possibility that the lone pair electrons, upon formation of the new N-H bond, will not stay unaltered in their sp2 hybrid orbital. Ab initio and semiempirical studies will be necessary in order to determine the charge distribution, the geometry and the force constants involving the unprotonated and protonated model Schiff's base. Hanson 33 33., (1983, submitted publication) indicated that upon protonation of mono- and di-substituted porphyrin, chlorin and bacteriochlorin Schiff's base -89- complexes the observed red shift in the visible spectrum can be attributed to a drOp in energy of the Schiff's base C=N n orbitals which then mix with the n orbitals of the porphyrin models. Therefore, similar calculations can be carried out in the unprotonated and protonated aromatic Schiff's bases, together with a Raman excitation profile to study the red shift observed in the U.V. spectra of the model Schiff's bases. LIST OF REFERENCES LIST OF REFERENCES Aton, B.; Doukas, A.G.; Narva, D.; Callender, R.H.; Dinur, V. and Honis, B. (1980) Biophys. J. g2, 79-94. Besnainou, S.; Thomas, B. and Bratoz, S. (1966) J. Mol. Spect. 33, 113-124. Blatz, P.E. and Mohler, J.M. (1975) Biochemistry 3:, 2304-2309. Botschwina, P. (1974) Chem. Phys. Lett. 32, 580-584. Braloz, S. and Besnainou, S. (1961) J. Chem. Phys. 3;, 1142-1147. Brown, R.D. and Penfold, A. (1957) Trans. Faraday Soc. 3;, 397-402. Christen, D.; Oberhammer, H.; Hammaker, R.M.; Chang, S. and DesMarteau, D.D. (1982) J. Am. Chem. Soc. 104, 6186-6190. Cordes, E.H. and Jencks, W.P. (1963) J. Am. Chem. Soc. 2;, 2843-2848. Datin, A.P. and Lebas, J.M. (1969) Spectrochim. Acta 25A, 169-185. El-Aasser, M.; Abdel-Halim, F. and El-Bayoumi, M.A. (1971) J. Am. Chem. Soc. 2;, 586-592. Elguero, J.; Gil, R. and Jacquer, R. (1967) Spectrochim. Acta 23A, 383. Fabian, M.J.; Legrand, M. and Poirier, P. (1956) Bull. Soc. Chim. Fr., 1499-1509. Favrot, J.; VOcelle, D. and Sandorfy, C. (1979) Photochem. Photobiol. 32, 417-421. Goulden, J.D.S. (1953) J. Chem. Soc., 997. -90- -9]_- Hanson, L.K.; Chang, C.K.; Ward, B.; Callahan, P.M.; Babcock, G.T. and Head, J.D. J. Am. Chem. Soc. submitted. Heyde, H.E.; Gill, D.; Kilponen, R.G. and Rimai, L. (1971) J. Am. Chem. Soc. 2;, 6776-6780. Howell, J.M. (1976) J. Am. Chem. Soc. 2;, 886-887. Layer, R.W. (1963) Chem. Rev. 2;, 489-510. Leonard, N.J. and Paukstelis, J.V. (1963) J. Org. Chem. 3;, 3021-3024. Marcus, M.A., Lemley, A.T. and Lewis, A. (1979) J. Raman Spect. 3, 22-25. Massing, G.; Stockburger, M.; Gortner, W.; Oesterhelt, D. and Towner, P. (1982) J. Raman Spect. 3;, 287-294. Ohta, N. and Ito, M. (1977) Chem. Phys. 3, 71-81. Ottolenghi, G. (1980) Adv. Photochem. 3;, 97-200. Parry, K.A.W.; Robinson, P.J.; Soinburry, P.J. and Waller, M.J. (1970) J. Chem. Soc. 422' 700-703. Patai, S. (1970) The Chemistry 33 Carbon-Nitrogen Double Bond, Chapter 1, IntersEience Publishers, New York. Persessy, A. (1973) Tetrahedron 32, 3207-3212. Santerre, G.M.; Hansrote, C.J. and Crowell, T.I. (1958) Jo AI“. Chem. SOC. Q, 1254-12570 Schmid, E.D.; Schlenker, P. and Brand, R.R. (1977) J. Raman Spect. 3, 314-318. Schmid, E.D. and Topsom, R.D. (1981) J. Am. Chem. Soc. 103, 1628-1635. Seth-Paul, W.A. (1981) J. Mol. Struct. Lg, 151-167. Sharma, O.P.; Singh, S.N. and Singh, R. (1974) Indian J. Phys. 2;, 494-503. Sharma, G.M. and Roels, O.A. (1973) J. Org. Chem. 38, 3648-3651. ‘— Silverstein, R.M.; Clayton, G.M. and Morrill T.C. (1981) Spectrometric Identification of Or anic Compounds, 4th ed., Wiley, New York, pp._I97-I§8. -92- Steel, W.L. (1964) Dissertation Abst. 3;, 61. Ward, B.; Callahan, P.M.; Young, R.; Babcock, G.T. and Chang, C.K. (1983) J. Am. Chem. Soc. 195, 634-636. Witkop, B. and Beiler, T.W. (1954) J. Am. Chem. Soc. ;g, 5589-5597. Wolfe, S.; Schlegel, H.B. and Whangbo, M.H. (1976) Can. J. Chem. 22' 795-799. Yanovskaya, L.A.; Kryshtal, G.V.; Yakovlev, I.P.; Kucherov, V.F.; Simkin, B.Y.; Bren, V.A.; Minkin, V.I.; Osipov, O.A. and Tumakova, I.A. (1973) Tetrahedron 32, 2053-2064. Zwarich, R.; Smolarek, J. and Goodman, L. (1971) J. Mol. Spect. 3;, 336-357.