Isolated C-D Stretching Vibrations as a Tool for Conformational

(n = 3 4 , and l-bromoalkanes-2-dl, CH3(CH2),3CHDCH2Br (n = 3-6), have been measured in the liquid and solid states and in an argon matrix. The confor...
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J. Phys. Chem. 1993,97,5530-5534

Isolated C-D Stretching Vibrations as a Tool for Conformational Analysis of Alkyl Chains. Raman and Infrared Spectra of 1-Bromoalkanes-1 4 1 and - 2 - 4 Keiichi Ohno,’ Yoshinori Takagi, and Hiroatsu Matsuura Department of Chemistry, Faculty of Science, Hiroshima University, Kagamiyama. Higashi-Hiroshima 724, Japan Received: January 28, 1993; In Final Form: March 18, 1993

The conformationaldependenceofthe wavenumbers of theisolated C-D stretchingvibrations for monodeuterated 1-bromoalkanes is reported. The Raman and infrared spectra of 1-bromoalkanes-1-dl, CH3(CH*),$HDBr (n = 3 4 , and l-bromoalkanes-2-dl, CH3(CH2),3CHDCH2Br (n = 3-6), have been measured in the liquid and solid states and in an argon matrix. The conformational dependence of the isolated C-D stretching vibrations in these molecules has been examined on the basis of the spectral observations for the different phases. It has been found that the isolated C-D stretching wavenumbers of 1-bromoalkanes- 1 - 4 depend significantly upon the conformation about the CH2CH2-CHDBr axis and those of 1-bromoalkanes-241 depend upon the conformation about both the CH2CHD-CH2Br and the CHzCHrCHDCHzBr axes. The stretching wavenumber of the isolated C-D bond trans to the C-C bond is 8-12 cm-l higher than that of the C-D bond gauche to the C-C bond, and the stretching wavenumber of the isolated C-D bond trans to the C-Br bond is 22-35 cm-l lower than that of the C-D bond gauche to the C-Br bond. It is shown that the isolated C-D stretching vibrations are effectually utilized as a tool for conformational analysis of alkyl chains. The ease of preparing monodeuterated alkyl compounds, as compared with monoprotonated deuteroalkyl compounds previously studied, encourages extensive applications of this method to practical conformational studies.

Introduction The conformation of molecules is of growing importance in the fields of biological and related sciences, since the characteristic properties of biological and functional substances are governed by their conformations. For conformational analysis, many experimental methods have been employed’ and vibrational spectroscopy, among others, has proved to be one of the most powerful techniques. In fact, a number of useful infrared and Raman key bands to conformational states have been established for a variety of compounds. The wavenumbers of the C-X stretching vibrations (X = C1, Br, S,Se, Si, etc.) are well-known to depend upon the conformation of the alkyl groups substituted by the relevant heterogeneous atom^.^-^ The infrared and Raman marker bands of n-alkyl chains in various conformational states, which include the kink, double-gauche, and end-gauche conformations, have been extensively studied.I”l3 The deuteration technique has also been applied effectively to the conformational analysis by vibrational spectroscopy; the isolated CD2 rocking vibration has been found to provide useful key bands to the conformation of alkyl chains.I”l6 In the present study, we propose a deuteration method which uses isolated C-D stretching vibrations to determine the conformation of specified part of the alkyl chain. Previously, deuterium-isolatedC-H stretching vibrations of monoprotonated deutero-n-alkanes, in which just one of the hydrogen atoms is protium and any others have been replaced by deuterium, have been extensively studied,l78I8 and ab initio molecular orbital calculationshave revealed the relation between the C-H stretching wavenumber and the local conformation in the immediatevicinity of the C-H bond.I9-23 The specifically monoprotonated deuteroalkylcompounds which the previous authors used are, however, usually difficult to prepare, unless the pertinent deuterated compounds are available,and extensive applicationsof this method to practical conformational analyses, in particular, of complex compounds of biological interest, are not always possible. On the other hand, the alkyl compounds, in which only one specific hydrogen atom is replaced by deuterium, are in general much easier to prepare. The isolated C-D stretching vibrations of the monodeuterated compoundshave therefore the potential of being 0022-3654/93/2097-5530$04.00/0

used as conformationalmarkers more extensively than the isolated C-H stretching vibrations. Since the synthetic introduction of deuterium into any desired site in the alkyl chain is possible, the relevant C-D stretching vibration makes possible the determination of the conformational state of that particular part, or eventually whole, of the chain. Aiming at establishing experimentally a relation between the wavenumber of the isolated C-D stretching vibration and the associated local conformation and at demonstrating usefulness of this conformational probe, we have studied the Raman and infrared spectra of monodeuterated 1-bromoalkanes, namely, 1-bromoalkanes-l-dl, CHs(CH2),+2CHDBr (n = 3 4 , and 1-bromoalkanes-2-dl, CHj(CH&3CHDCHzBr (n = 3-6).

Experimental Section 1-Bromoalkanes-1-dlwere prepared by reducingpertinent alkyl aldehydes with LiAID4 (98 at. 55 D) in diethyl ether, and the resultant alcohols were brominated with PBr3.24 1-Bromoalkanes2-dl were prepared by adding DBr to pertinent alkenes with dibenzoylperoxide as catalyst.2s Deuterium bromidewas prepared by adding D20 (99.9 at. 9% D)to PBr3. The substances obtained were purified by distillation and their purities were checked by gas chromatography.26 The Raman spectra in the liquid and solid states were recorded on a JEOL JRS-400D spectrophotometer with an NEC GLG3200 argon-ion laser. The solid-state spectra were measured for the sample in an ampoule held on a copper block cooled with liquid nitrogen. The infrared spectra were recorded on a JEOL JIR-40X Fourier transform spectrophotometer at a resolution of 1 cm-I with a glober source and a TGS detector. In the infrared measurements,the gaseoussample or a mixture of the sample and argon was slowly sprayed onto a CsI plate maintained at 11 K with an Iwatani CryoMini DlOS refrigerator. Results

Determination of the Conformation of l-BromoaLknoes-l-dl and -2-4. The conformation of I-bromoalkanes has been well 0 1993 American Chemical Society

The Journal of Physical Chemistry, Vol. 97, No. 21, 1993 5531

Isolated C-D Stretching Vibrations I

'

'

'

'

' : / I

! I '

'

600 400 Wavenumberlcm-1

'

'

200

'I

I

0

Figure 1. Raman spectra of 1-bromoalkanes-1-4 and -2-dl: (a) CH3(CH2)2CHDBr, (b) CH,(CH2)3CHDBr, (c) C H ~ C H Z C H D C H T Br, and (d) CH3(CH2)2CHDCH2Br. The upper and lower spectra for the respective compounds are those in the liquid and solid states,

respectively. established on the basis, in particular, of the C-Br stretching vibrationas a key to the conformationabout the CC-CBr axis,3.27,28 and of the accordion vibration in the solid ~ t a t e . The ~ ~ infrared ,~~ spectra and the conformational analysis of 1-bromopropane-1-dl and -2-4 have been reported previ0usly.2~ Figure 1 shows the Raman spectra of 1-bromoalkanes- 1-dl and -2-dl, namely, CH3(CH2),2CHDBr and CH3(CH2),3CHDCH2Br ( n = 4 and 5), in the region below 700 cm-I; the upper and lower spectra for the respective compounds are those in the liquid and solid states, respectively. In the liquid state, the C-Br stretching vibration is assigned to the strong band at about 630 cm-1 and the two strong bands at about 550 cm-I. The former and the latter are associated, respectively, with the trans conformation and the two nonequivalent gauche conformations about the CC-CBr axis, as shown in Table I. Normal coordinate calculationswith computer program MVIB3O have indicated that the C-Br stretching vibration is not greatly affected by the conformational state of the CC-CC axes. The persistence of the band at about 630 cm-I in the solid state indicates that the conformation about the CCCBr axis is trans. In the solid state, another strong Raman band is observed in the 100-500-~m-~ region. This band is assigned to the accordionvibration of the all-trans conformer;the observed and calculated wavenumbers of the accordion vibration are given in Table I. In the liquid state, the enthalpy difference between the gauche (G) and trans (T) conformers, HG - HT,for 1-bromopropanehas been determined to be about -100 cal mol-I by Raman intensity mea~urements.2~ The previous studies have indicated the existence of the TT, TG, GT, and GG conformers for 1-bromobutane CH3CH2-CH2-CH2Br27and of the TTT, TTG, TGT, GTT, TGG, GTG, GTG', and GGG conformers for 1-bromopentane CH3CH2-CH2-CH&H2Br.28 The Raman spectra of 1-bromoalkanes-1-dland -2-dl in the skeletal deformation region of 100-500 cm-1 are similar to those of the corresponding undeuterated species. Thus, it is confirmed for 1-bromoalkanes-1-dland -2-4 that severalconformersare present in the liquid state and only the all-trans conformer persists in the solid state. Subatituent Effect of the Isolated C-D Stretching Vibrations. The Raman spectra in the C-D stretching region for l-bromoalkanes- 1-dl and -2-dl are shown in Figure 2, and the observed C-D stretching wavenumbers and the assignments are given in Table 11. Excepting 1-bromopropane-1-dl and -2-dl, the C-D

stretching wavenumbersin the solid state are approximately 22 15 cm-I for 1-bromoalkanes-1-dl and approximately 2 160 cm-1 for 1-bromoalkanes-241. The difference in these wavenumbers is ascribed to an inductive effect of a polar substituent of bromine through the carbon ~hain.3~ The intrinsic wavenumber for the isolated C-D stretching vibrations of the -(CH2)nCHD(CH2)mchain is likely to be around 2139 cm-1 as estimated from the C-D stretching wavenumbers for 1-bromododecane-6-dland -8-dI.32 For 1-bromopropane-1-dl and -2-dl,the isolated C-D stretching vibrations are influenced by the alkyl end group. Conformational Dependence of the Isolated C-D Stretching Vibrations. As shown in Figure 2, l-bromoalkanes-l-dl and -2dl give two or more C-D stretching bands in the liquid state, in contrast with one primary strong band, with some additional weaker bands, in the solid state. The primary band in the solid state is obviously assigned to the all-trans conformer with the C-D stretching vibration at the C1 position of l-bromoalkanes1-dl or at the C2 position of 1-bromoalkanes-2-dl. The minor weaker bands in the solid state are ascribable to combination and/or overtone vibrations; the intensities of these bands are perhaps enhanced by possible Fermi resonances with the C-D stretching vibration. For 1-bromopropane-1-dl, a prominent band and a shoulder areobservedin theliquidstateat 2214and2203 cm-],respectively, and the former disappears but the latter persists on solidification (Figure 2a). The higher-wavenumber band is thus assigned to the gauche conformation about the CH3CH2-CHDBraxis and the lower-wavenumberband to the trans conformation. Spectral changes in the C-D stretching region on solidification for the longer homologues of 1-bromoalkanes-1-dl (Figure 2b-d) are similar to those for 1-bromopropane-1-dlexcept that the wavenumbers for the longer homologues are systematically slightly higher than those for the bromopropane. The whole bandwidth of the two C-D stretching vibrations in the liquid state is substantially constant (27-32 cm-I) for these longer homologues. The constancy of the bandwidth indicates that the isolated C-D stretching vibrations of 1-bromoalkanes-1-dl are influenced essentially only by the conformational state of the CH2CH2CHDBr axis just adjacent to the C-D bond. Thus, the C-D stretching bands at 221&2215 cm-I, which persist in the solid state, are now established to be due to the trans conformation about the CH2CH2-CHDBraxis and the bands at 2220-2223 cm-l due to the gauche conformation. For 1-bromopropane-241, two appreciably strong bands are observed in the liquid state at 2143 and 2178 cm-I, and only the latter persists in the solid state (Figure 2e). The higherwavenumber band is assigned to the C-D stretching vibration for the trans conformation about the CH3CHD-CH2Braxis and the lower-wavenumber band to the vibration for the gauche conformation. Similar spectral changes in going from the liquid to the solid state are also observed for the longer homologues of 1-bromoalkanes-2-dl (Figure 2f-h), but the wavenumbers for the longer homologues are slightly lower than those for the bromopropane. The band around 2170 cm-I observed for the longer homologues in the liquid state is, however, significantly broad with a width of about 55 cm-I, which is compared with the singlebandwidth for 1-bromopropane-2-dl and 1-bromoalkanes1-dl (15-24 cm-I). This observation suggests the overlap of several bands in this wavenumber region. In order to clarify this possibility, infrared spectra were measured for 1-bromoalkanes2 4 , CH3(CH2),jCHDCH2Br (n = 4-6), in an argon matrix. The matrix-isolation spectra shown in Figure 3 reveal that the broad band around 2170 cm-1 in the liquid state is actually composed of several separate bands. The comparison of the matrix-isolationand solid-state spectra shows that the prominent band at about 2160 cm-l for the matrix is also observed for the solid state but the other prominent band at about 2170 cm-l is missing in the solid state. This spectral feature is elucidated by

Ohno et al.

5532 The Journal of Physical Chemistry, Vol. 97,No. 21, 1993

TABLE I: Observed and Calculated C-Br Stretching and Accordion Wavenumbers (cm-I) for I-Bromoalkanes-1-dland -2-d1 ~

~

~

~

~

Raman

Raman’ obsd

obsd

compound

liquid

solidb

Calcd

C3H6DBr-l-dl

620 554 sh 541 312 621 559 sh 550 219 621 561 sh 552

61 1

61 1 548

C4HgDBr-1-dl

C5HloDBr-l-dl

220 C6H12DBr-1-dl

620 560 sh 550 198

312 61 1 218 616

{E 617

540 313 608 550 542 219 609 550 542 214 615 551 542

compound CsHsDBr-2-dl

C4H~DBr-2-dl

CsHloDBr-2-dl

C6Hl2DBr-2-dl

liquid 640 541 531 308 64 1 55 1 531 211 64 1 552 539 218 642 552 539 199

solidb 632 308 631 280 639

$:: 639

calcd 64 1 551 539 31 1 64 1 553 541 216 640 553 541 213 641 554 542 193

assignment‘ C-Br str(T) C-Br str(G) C-Br str(G’ ) accord

C-Br str(T) C-Br str(G) C-Br str(G’ ) accord C-Br str(T) C-Br str(G) C-Br str(G‘ ) accord C-Br str(T) C-Br str(G) C-Br str(G’ )

20 1 193 200 accord Key: sh, shoulder. Wavenumbers for the all-trans conformer. C-Br str, the C-Br stretching vibration; accord, the accordion vibration of the all-trans conformer; T, G, and G’, the trans, gauche, and gauche prime conformations, respectively, about the CC-CBr axis.

n

2200

I

2000

2200

2000

Wavenumber/cm-1 Figure 2. Raman spectra of 1-bromoalkanes-1-dland - 2 4 : (a) CH3CH2CHDBr, (b) CH3(CH&CHDBr, (c) CH3(CHz),CHDBr, (d) CH,(CH2)4CHDBr, (e) CHjCHDCH2Br, (f) CH~CHZCHDCH~B~, (g) CH,(CH&CHDCH*Br, and (h) C H I ( C H ~ ) ~ C H D C H ~The B ~upper . and lower spectra for the respective compounds are those in the liquid and solid states, respectively.

the conformational state of another associated bond axis CHICH&HDCH2Br, because 1-bromopropane2-d1, which does not contain the corresponding axis in the molecule, shows no such spectral feature. Thus, for the longer homologues of l-bromoalkanes-2-dl, the band at about 2160 cm-I observed in the solid state is assigned to the trans-trans conformation about the CH2CH2-CHD-CH2Braxes, whilethebandsatabout 2130and2170 cm-I, not observed in the solid state, are assigned to the gauche conformation about the CH2CHD-CH2Br axis and the CH2CH2-CHDCH2Br axis, respectively.

Discussion The experimental results for 1-bromoalkanes-1 - 4 indicate that the bands at 2210-2215 and 2220-2223 cm-I are assigned to the C-D stretching vibrations of the trans and gauche conformations, respectively, about the CH2CH2-CHDBr axis. In molecules of monodeuterated 1-bromoalkanes, the carbon atom, with which the deuterium is bound, is an asymmetric center, giving optically isomeric R- and S-configurations. The substances of l-bromoalkanes-l-dl and -2-4 employed in the present work actually consist of the two configurations. (R)-1-Bromoalkane-1-dl or (S)-1-bromoalkane-1-dl has two nonequivalent gauche conformations about the CH2CH2-CHDBraxis; Figure 4 shows three different conformers of (R)-1-bromopropane-1-dl with the isolated C-D bond indicated. The figure also shows nine different conformers of (S)-l-bromobutane-2-d1. The C-D stretching wavenumbers for the different conformations may be evaluated on the basis of the previous results for the deuterium-isolated C-H stretching waven~mbers.1~,~~~~~.23 McKean et a1.17J8 have studied the conformational dependence of the isolated C-H stretching vibrations of the CHD2 group in monoprotonated 2-halogenodeuteropropanes. It has been found that the stretching wavenumbers of the isolated C-H bond trans to the C-C bond is 14-19 cm-I higher than that of the C-H bond trans to the C-D bond and that the stretching wavenumber of the isolated C-H bond trans to the C-Br bond is 35 cm-1 lower than that of the C-H bond trans to the C-D bond. Synder et al.22,23have later shown for simple monoprotonated n-deuteroalkanes that the C-H bond lengths calculated by an ab initio molecular orbital method depend upon the local conformation and are correlated linearly with the observed isolated C-H stretching wavenumbers; the stretching wavenumber of the isolated C-H bond trans to the C-C bond is 11 cm-l higher than that of the C-H bond trans to the C-D bond. Theconformational dependence of the isolated C-H stretching vibrations established previously may be correlated with that of the isolated C-D stretching vibrations for 1-bromoalkanes-1-dl and -2-4. For (R)-1-bromopropane-1-dl (Figure 4), the C-D bond in the trans (T) and gauche (G)conformers is trans to the C-H bond, and the C-D bond in the gauche prime (G’ ) conformer is trans to the C-C bond. Thus, in accordance with the interpretation of the isolated C-H stretching vibrations,17’18.22‘23 the band at 2203 cm-I is assigned to theC-D stretchingvibrations of the T and G conformers and the band at 2214 cm-l is assigned to the C-D stretching vibration of the G’ conformer, indicating that the C-D stretchingwavenumbersfor the G and G’conformers are different from each other. For the interpretationof the isolated

Isolated C-D Stretching Vibrations

The Journal of Physical Chemistry, Vol. 97, No. 21, 1993 5533

TABLE II: Observed Vibrational Wavenumbers (cm-l) and Assignments for l-BromoaUranes-l-dl and -2-4 in the Region 2000-2300-~m-~

Raman' compound

liquid

C3H6DBr-1-dl

2241 vw

CbHsDBr- 1-dl

2214 m 2203 sh, w 2243 sh, w

CsHloDBr-l-dl C6H12DBr-I-dl C~H6DBr-2-dl

C4HsDBr-2-dl

2220 m 2210 m 2223 sh, w 2214 m 2222 sh, w 2212 m 2191 vw 2178 m 2155 vw 2143 m 2175 b, m 2168 m 2155 m 2133 m

CsHloDBr-2-dl

infrared"9C solidb

2215 w 2215 w 2205 vw 2173 w 2150 vw

2166vw 2155 w 2135 vw 2181 vw

2126 vw

C6H12DBr-2-dl 2167 b, w 2159 w 2132 vw

2 x 1120 1120 1093 4CDJ V(CDg) 2 X 1128 1128 1103 V(CDt) V(CDB) 4CDt) V(CDg) V(CDt) V(CDg) 1185 + 1018 4CD.g) 1135 + 1018 4CD.J 1223 959 V(CD1g) 1264 901 V(CDgg) V(CDgt) 1184 959 1138 1047 V(CD1g) V(CDg,) 1096 1050 1096 1047 V(CD81) 1180 951 1230 961 V(CDg0 V(CDgg) 1134+ 1020 V(CDg1) 1134+ 1001

+

2213 m

2182vw

assignmentd

+

2201 w 2254 vw 2233 vw

2160 w

2130 w

solidb

2238 vw 2214 vw

2173 b, m

2128 m

matrix

2185 sh, w 2166 m 2158 m 2135 m 2181 sh, w 2173 m 2163 m 2152 mw 2143 mw 2130 mw 2188 sh, w 2172 m 2160 m 2133 mw

2181 vw 2166vw 2155 m 2134 vw 2180 b, vw 2157 m 2148 w 2138 w 2127 vw 2185 vw 2159 m 2151 sh, w 2131 vw

+ +

+ +

+ +

+ +

a Key: m, medium; w, weak; v, very; sh, shoulder; b, broad. Wavenumbers for the all-trans conformer. Infrared spectra for CsH6DBr-l-dl, C4HsDBr-l-dl,CsHloDBr-l-dl, C6H12DBr-l-dl, and c&DBr-2-d, were not measured. The isolated C-D stretching vibrations, v(CD,) or v(CDXy), and combination and overtone vibrations are indicated. For the notation of the isolated C-D stretching vibrations, see text.

C-D stretching vibrations in relation to the relevant conformations, we propose new notation v(CD,,) and v(CD,), where x, y = t (trans) or g (gauche); the first subscript x denotes the conformationof the C-D bond with respect to the C-C bond, and the second subscript y, if any, denotes the conformation of the C-D bond with respect to the C-Br bond. The symbol denotes no relevant conformational axis present. In accordance with this notation, the bands at 2201-2215 cm-1 for 1-bromoalkanes-1-4, CH3(CH2),2CHDBr (n = 3 4 , are assigned to v(CDg) and the bandsat 2214-2223 cm-I are assigned to v(CDt). The stretching wavenumber of the isolated C-D bond trans to the C-C bond is thus 9-1 1 cm-1 higher than that of the C-D bond gauche to the C-C bond. For (S)-l-bromobutane-2-dl, nine conformers (Figure 4) are possible, but the GG' and G'G conformers are unlikely to exist because of the large steric hindrance. For 1-bromobutane,CH3C H A H A H 2 B r , Momany et al.33 have reported the conformational distribution of 36% TT,24% TG, 24% GT, and 16% GG in the gaseous state as determined by an electron diffraction method, and Ogawa et al.2' have reported the relative stability of the conformers being in the order of TG,GG,TT, and GT in the liquid state as estimated by Raman intensity measurements. For (S)-l-bromobutane-2-dl, the matrix-isolation infrared band at 2 166cm-l is assigned to v(CDtg)for the GT and GG conformers, the band at 2158 cm-1 to u(CD,) for the TT, TG, and G'T conformers, and the band at 2135 cm-1 to u(CDgt) for the TG' and G'G' conformers. For 1-bromoalkanes-2-dl CH3(CH2),3CHDCH2Br ( n = 349, it isshown that thestretching wavenumber of the isolated C-D bond trans to the C-C bond is 8-12 cm-l higher than that of the C-D bond gauche to the C-C bond and

*

the stretching wavenumber of the isolated C-D bond trans to the C-Br bond is 22-35 cm-I lower than that of the C-D bondgauche to the C-Br bond. These results indicate that the isolated C-D stretching vibrations of 1-bromoalkanes-2-dlselectively provide conformational information for the CH2CHD-CH2Br axis and the CH2CH2-CHDCH2Br axis. The above interpretation, based on the previous results for the isolated C-H stretching vibrations, on the relationship between the isolated C-D stretching vibrations and the associated local conformations is consistent with the experimental results mentioned before. The vibrational assignments of the isolated C-D stretching bands are summarized in Table 11.

Conclusions The present study has shown experimentally that the analysis of the isolated C-D stretching vibrations gives valuable information on the conformation of bromoalkyl chains. The C-D stretching wavenumbers of 1-bromoalkanes-1-dl depend significantly upon the conformation about the CHzCHz-CHDBr axis and those of 1-bromoalkanes-2-dldepend upon the conformation about both the CH2CHD-CH2Br and CHZCH2-CHDCHzBr axes. In some cases, complexity may oecur in the C-D stretching region due to the appearance of overtone and/or combination vibrations. The stretching wavenumber of the isolated C-D bond trans to the C-C bond is 8-12 cm-' higher than that of the C-D bond gauche to the C-C bond, and the wavenumber of the isolated C-D bond trans to the C-Br bond is 22-35 cm-I lower than that of the C-D bond gauche to the C-Br bond. These results show that the isolated C-D stretching vibrationsare effectuallyutilized

Ohno et al.

5534 The Journal of Physical Chemistry, Vol. 97, No. 21, 1993

is that the conformation at any desired position of the alkyl chain is determined explicitly if the pertinent monodeuteratedcompound is available. TheanalysisoftheisolatedC-D stretchingvibrations is also useful for studying configurationsof the molecule and for discriminating between the two nonequivalent gauche conformations. Further studies of the isolated C-D stretchingvibrations for other classes of compounds are now in progress. '

Acknowledgment. The present work was partially supported by a Grant-in-Aid for Scientific Research 02640370 from the Ministry of Education, Science, and Culture, Japan. We thank Mr. Yasuo Tatsumi for his assistance in the synthetic work. References and Notes (1) Brand, J. C. D.; Speakman, J. C.; Tyler, J. K. Molecular Structure: The Physical Approach, 2nd ed.; Edward Arnold: London, 1975. (2) Shipman, J. J.; Folt, V. L.; Krimm, S.Spectrochim. Acta 1962,18,

2300

2200

2100

21 0

Wavenumber/cm-1

Figure 3. Infrared spectra of 1-bromoalkanes-2-dl: (a) CH3CHzCHDCHZBr, (b) CH3(CHz)ZCHDCHzBr, and (c) CHJ(CHZ)~CHDCHZBr. The upper and lower spectra for the respective compounds are those in an argon matrix and in the solid state, respectively. (R)-1-Bromopropane-1-dl

w

n

TG' v(CDgI)

P Figure 4. Schematic representation of possible different conformers and the notation of the isolated C-D stretching vibrations for (R)-1bromopropane-1-dl and (S)-l-bromobutane-2-d,. Protium atoms are not shown in the figure. The notation is explained in the text.

as a tool for conformational analysis of alkyl chains. The ease of preparing monodeuteratedalkyl compounds,as compared with monoprotonated deuteroalkyl compounds previously studied, encourages extensive applications of this method to practical conformational studies of complex compounds. One of the important features of using the isolatedC-D stretching vibrations

1603-1613. (3) Bentley, F. F.; McDevitt, N. T.; Rozek, A. L. Spectrochim. Acta 1964, 20, 105-126. (4) Sugeta, H.; Go, A.; Miyazawa, T. Chem. Lett. 1972, 83-86. (5) Nogami, N.; Sugeta, H.; Miyazawa, T. Bull. Chem. SOC.Jpn. 1975, 48, 2417-2420. (6) Ohno, K.; Hirokawa, T.; Aono, S.;Mmata, H. Bull. Chem. Soc. Jpn. 1977, 50, 305-306. (7) Ohno, K.; Matsuura, H.; Murata, H. J . Mol. Struct. 1980,66,4564. ( 8 ) Murata, H.; Matsuura, H.; Ohno, K.; Sato, T. J . Mol. Struct. 1979, 52, 1-11. (9) Matsuura, H.; Ohno, K.; Sato, T.; Murata, H. J. Mol. Struct. 1979, 52, 13-26. (10) Snyder, R. G. J. Chem. Phys. 1967, 47, 1316-1360. (1 1) Zerbi, G.; Piseri, L.; Cabassi, F . Mol. Phys. 1971, 22, 241-256. (12) Maroncelli, M.;Qi,S. P.;Strauss,H. L.;Snyder, R.G.J.Am. Chem. SOC.1982, 104,6237-6247. (13) Jona, P.; Gussoni, M.; Zerbi, G. J . Appl. Phys. 1985,57,834-841. (14) Snyder, R. G.; Poore, M. W. Macromolecules 1973, 6, 708-715. (15) Maroncelli, M.; Strauss, H. L.; Snyder, R. G. J . Chem. Phys. 1985, 82, 281 1-2824. (16) Maroncelli, M.; Strauss, H. L.; Snyder, R. G. J . Phys. Chem. 1985. 89,43904395. (17) McKean, D. C.; Duncan, J. L.; Batt, L. Spectrochim. Acta, Part A 1973, 29, 1037-1049. (18) McKean, D. C. Chem. SOC.Rev. 1978, 7, 399-422, and references

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