W. C. Harris

Vibrational spectra and structure of esters—I. Infrared and Raman spectra of CH3COOCH3, CH3COOCD3, CD3COOCH3 and CD3COOCD3

Abstract The infrared spectra of gaseous, liquid and solid methyl acetate and its deuterium derivatives have been investigated from 4000 to 200 cm −1 . The absorption spectrum of the crystalline state of each isotope has also been measured down to 33 cm −1 , but the methyl torsional modes were not resolved. Raman spectra of the gaseous, liquid and solid states were obtained between 100 and 4000 cm −1 . It is concluded that methyl acetate is present as a single molecular conformation in the temperature range studied since there is a one to one correspondence between the infrared and Raman transitions measured at ambient and liquid nitrogen temperatures. An assignment of the 27 normal modes, based upon relative band intensities, isotopic shift ratios and group frequency correlations is presented.

Vibrational spectra and structure of 1,2‐difluoroethane: Gauche–trans conformers

Infrared and laser‐Raman spectra of 1,2‐difluoroethane (FH2CCH2F) have been recorded from 4000 to 50 cm−1. Whereas the Raman spectra were measured for all three physical states, the infrared data were recorded for the gaseous and crystalline phases. Spectral transitions associated with the predominant gauche conformer have been assigned with confidence on the basis of clearly defined infrared band contours and Raman depolarization ratios. Although several fundamentals have also been assigned for trans‐1,2‐difluoroethane, the majority of the normal modes associated with trans‐C2F2H4 appear to be unresolved or coincident with bands assigned to gauche‐C2F2H4. The magnitude of ΔH separating the two conformers was determined to be 1.98±0.08 kcal/mole by measuring the temperature dependence of the Raman bands assigned to the F–C–C–F bending modes for gauche (503 cm−1) and trans (461 cm−1) C2F2H4, respectively. An overall potential function describing the torsional barriers and ΔH will be discussed on the basis ...

Low‐frequency vibrational spectra and ring puckering of cyclopentene‐d8

More than 25 ring‐puckering transitions have been observed in the vapor‐phase Raman and far‐infrared spectra of cyclopentene‐d8. The ring‐puckering potential energy function in reduced form was determined to be V=18.20(Z4−6.88 Z2) cm−1 which represents a barrier to inversion of 215 cm−1 (0.61 kcal/mole). The barrier differs from that of the undeuterated cyclopentene by 17 cm−1 owing to mixing of other motions (presumably CH2 rockings). The equilibrium value of the molecule is calculated to have a dihedral angle of 26°.

Vibrational spectra and normal coordinate analysis for cyclopentene, cyclopentene-1-d1, cyclopentene-1,2,3,3-d4 and cyclopentene-d8

Abstract The vibrational spectra of cyclopentene, cyclopentene-1-d 1 , cyclopentene-1,2,3,3-d 4 and cyclopentene-d 8 have been measured between 4000 and 100 cm −1 in all three physical states. In conjunction with a normal coordinate analysis, vibrational assignments are proposed on the basis of isotopic shift ratios, group frequency considerations, relative band intensities and shapes as well as depolarization ratios. The vibrational assignments and coupling effects are discussed in terms of the calculated potential energy distribution. A total of thirty-seven valence force constants was used to calculate the one hundred and twenty-eight frequencies for the four isotopic derivatives of cyclopentene. The correspondence between the observed and calculated frequencies is reflected by the overall percentage error of about 1%.

Vibrational spectra and structure of nitrogen containing molecules—III. Acetone azine and acetone azine-d12☆

Abstract The i.r. spectra of (CH 3 ) 2 Cue5fbNue5f8Nue5fbC(CH 3 ) 2 and (CD 3 ) 2 Cue5fbNue5f8Nue5fbC(CD 3 ) 2 have been studied from 4000 to 300 cm −1 in all three physical states. Absorption spectra for the polycrystalline samples were also obtained down to 33 cm −1 . Raman spectra for liquid and crystalline acetone azine and acetone azine- d 12 were recorded between 4000 and 100 cm −1 . Since mutual exclusion was observed for the i.r. and Raman bands assigned to the skeletal modes of acetone azine, the spectral data have been interpreted in terms of C 2 h molecular symmetry. An assignment of the fundamental vibrations is based upon the observed isotopic shift ratios, depolarization measurements, relative band intensities and positions. The methyl torsional modes were assigned to bands at 235 and 215 cm −1 , respectively, in the Raman spectrum of crystalline acetone azine. The frequencies associated with the Cue5fbN and Nue5f8N stretching modes of acetone azine suggest the π electrons may not be localized and this observation is consistent with the bond orders for the Cue5fbN (1.9) and Nue5f8N (1.5) groups calculated from simple molecular orbital theory. The results of the present study are compared with the data recently reported for tetramethylhydrazine and tetramethyltetrazine.

Vibrational spectra and structure of esters—II. Raman spectra and potential function calculations for HCOOCH3, DCOOCH3 and HCOOCD3

Abstract Raman spectra of the gaseous, liquid and crystalline states have been recorded for HCOOCH3, DCOOCH3 and HCOOCD3. The vibrational data for methyl formate are consistent with acis-planar skeletal structure and there is no evidence for a secondgauche ortrans conformation. A vibrational analysis for HCOOCH3 based upon depolarization measurements, relative band intensities and positions, in addition to isotopic shift ratios, is briefly outlined. The vibrational assignment has been correlated with previous i.r. studies and is consistent with product rule calculations. An assigmnent for the 1 ← 0 methyl torsional transition for each of the respective isotopes is based upon difference tones observed in the low frequency Raman spectra of the liquid state. The magnitude of the internal rotational barrier for the methyl group is 1.22, 1.13 and 1.11 kcal/ mole for thed0,d1 andd3 compounds. A value of 68.8 kcal/mole is calculated forV* for the C O torsion by using the observed Raman line at 338 cm−1 and microwave structural parameters. The magnitude and nature of the C O torsional barrier is discussed in detail.

Raman spectra and internal rotation of 1,1‐dimethylcyclopropane and 1,1‐dimethyl‐d6‐cyclopropane

The Raman spectra of gaseous and crystalline 1,1‐dimethylcyclopropane and 1,1‐dimethyl‐d6‐cyclopropane are reported for the frequency region between 100 and 600 cm−1. Assignment of the Raman shifts at 251 and 228 cm−1 for solid 1,1‐dimethylcyclopropane to the b2 and a2 torsional modes is supported by the spectral data recorded for the deuterium analog. In addition, the 2←0 transition for the b2 torsional mode is observed at 460 and 462 cm−1 in the spectra of gaseous and liquid 1,1‐dimethylcyclopropane. Whereas the internal rotational barrier for solid 1,1‐dimethylcyclopropane is calculated to be 3.7 kcal/mole on the basis of the low temperature frequency data, it is estimated the barrier is on the order of 3.2 kcal/mole for the gaseous state. The internal rotational parameters determined for solid and gaseous 1,1‐dimethylcyclopropane are compared with barrier heights determined previously for molecules with C(sp2)–C(sp3) and C(sp3)–C(sp3) single bonds.

Vibrational spectra and structure of nitrogen containing molecules—I. Formaldehyde dimethylhydrazone

Abstract The i.r. spectrum of formaldehyde dimethylhydrazone, (CH 3 ) 2 NNue5fbCH 2 , has been studied from 3400 to 200 cm −1 in the gaseous state and between 3400 and 140 cm −1 at liquid nitrogen temperatures. A comparison of the vibrational spectra in the solid and fluid states indicates the molecule exists in only one conformer in all three physical states. The Raman spectra of the gas, liquid and solid have also been recorded and depolarization values measured. In view of the number of polarized Raman lines, the vibrational spectra have been interpreted in terms of C 1 symmetry. A vibrational assignment is presented based upon the observed band positions, intensities and group frequency considerations. Whereas the methyl torsional modes were assigned to bands at 271 and 241 cm −1 in the absorption spectrum of solid (CH 3 ) 2 NNue5fbCH 2 , the counterparts to these transitions were centered at 258 and 239 cm −1 in the Raman effect. A similar difference in the i.r. and Raman frequencies of other fundamentals was ago observed and these splittings have been attributed to the correlation field. A low frequency i.r. spectrum of (CH 3 ) 2 NNue5fbCH 2 isolated in an argon matrix was also studied and is compared to the spectra obtained for the crystalline state.

Vibrational spectra and structure of nitrogen containing molecules—II

Abstract The i.r. spectra of 3,3-dimethyldiaziridine and 3,3-dimethyl- d 6 -diaziridine have been recorded for the gaseous and crystalline states between 300 and 4000 cm −1 . An absorption spectrum of solid 3,3-dimethyldiaziridine between 70 and 300 cm −1 was also measured. Raman spectra of liquid and crystalline 3,3-dimethyldiaziridine have been recorded from 100 to 4000 cm −1 . A vibrational assignment is developed for the molecule in terms of the C 2 point group and the proposed description for the 33 normal modes is based upon isotopic shift ratios, frequency perturbations resulting from hydrogen bonding, and by comparing the data with assignments presented previously for other three-membered ring compounds.