摘要:

AbstractThe Raman (3500–20 cm−1) and infrared (3500–50 cm−1) spectra of gaseous and solid cyclo‐propylmethyltrifluorosilane, c‐C3H5CH2SiF3, were recorded. Additionally, the Raman spectrum of the liquid was obtained along with qualitative depolarization values. The spectra of the gas and liquid were interpreted on the basis of the predominance of a conformation having agauchestructure and this form exists exclusively in the solid. Spectral evidence to support the existence of a higher energycisconformer where the SiF3group iscisto the cyclopropyl ring is observed in the Raman spectra of the gas and liquid. From studies of the Raman spectra at various temperatures, the conformational enthalpy difference was determined to be 490 ± 122 cm−1(1.4 ± 0.35 kcal mol−1) and 548 ± 110 cm−1(1.57 ± 0.32 kcal mol−1) (1 kcal = 4.184 kJ) for the gas and liquid, respectively. The cyclopropyl torsion was observed as a weak infrared band centered at 77 cm−1in the spectrum of the gas. A complete assignment of the normal vibrational modes is provided.Ab initiocalculations utilizing the RHF/6‐31G* and MP2/6‐31G* basis sets are consistent with thegaucherotamer lying 554 cm−1(1.6 kcal mol−1) and 296 cm−1(0.85 kcal mol−1), respectively, lower in energy than thecisconformation. It is estimated that there is only 4–10% of the higher energy conformer present in the vapor at ambient temperature. Optimized structural parameters were obtained for both conformers with both basis sets and the results should provide good starting parameters for the analysis of the electron diffraction data. The force field obtained with the RHF/6–31G* basis set was used to perform a normal coordinate analysis. These results are compared with correspond

ISSN:0377-0486    

DOI:10.1002/jrs.1250250902

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Raman (3200–30 cm−1) and infrared (3200–50 cm−1) spectra of 1,1‐dichloromethyl methyl ether are reported for the gas, liquid, amorphous solid and annealed polycrystalline solid. These spectral data were interpreted on the basis that in the fluid phases there is a mixture of trans and gauche conformers but only the trans conformer remains in the annealed solid. From the temperature‐dependent relative intensity of Raman bands at 379 and 427 cm−1in the liquid, an enthalpy difference of 656 ± 84 cm−1(1.88 ± 0.24 kcal mol−1or 7.85 ± 1.0 kJ mol−1) was obtained with the trans conformer the more stable form. Complete vibrational assignments are made for the much more abundant trans form, and a number of fundamentals are assigned for the gauche conformer with the aid of ab initio computations made with the 3–21G and 6–31G* basis sets. The harmonic force fields obtained using the 3–21G basis set are reported for both conformers together with scaled and unscaled wavenumbers and the accompanying potential energy distributions. The results are compared with the corresponding quantities obtaine

ISSN:0377-0486    

DOI:10.1002/jrs.1250250903

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractRaman spectra of solid trifluoroiodomethane are reported for both the lattice and internal mode regions for samples at temperatures between 12 and 130 K. A solid‐state phase transition at about 115 K is confirmed. Above this temperature, the spectra are characteristic of a disordered or highly anharmonic solid. At low temperatures, the spectra are compatible with an ordered, harmonic molecular crystal with a unit cell containing at least four molecules. Plausible assignments of all observed spectroscopic features are propose

ISSN:0377-0486    

DOI:10.1002/jrs.1250250904

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Raman (3200–20 cm−1) and infrared (3200–35 cm−1) spectra of 3‐bromo‐2‐methylpropene, H2CC(CH3)CH2Br were recorded for the gas and solid. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values were obtained. The fundamental asymmetric torsional mode for thegaucheconformer is observed at 81.5 cm−1with one excited state falling at a lower wavenumber but the asymmetric torsion is not observed for the higher energys‐cisconformer. Utilizing thegaucheobserved torsional wave numbers, thegauchedihedral angle, the enthalpy difference between conformers and the calculated torsional fundamental wavenumber for thes‐cisconformer, the potential function governing the interconversion of the rotamers was estimated. This potential function gives values of 170 cm−1(486 cal mol−1) (1 cal = 4.184 J), 2659 cm−1(7.60 kcal mol−1) and 725 cm−1(2.07 kcal mol−1) for thes‐cis to gauche, gauche to gauche and gauche to s‐cisbarriers, respectively, and it is compared with tht obtained with the RHF/STO‐3G* basis set. From the methyl torsional wavenumber of 172 cm−1for thegaucheconformer, the threefold barrier of 695 cm−1(1.99 kcal mol−1) was calculated for the methyl group. A complete vibrational assignment is proposed based on Raman : depolarization data, group wavenumbers and relative infrared and Raman intensities. The conformational energy difference and optimized geometries of both conformers were also obtained fromab initiocalculations with the RHF/STO‐3G*, RHF/LANL1DZ and MP2/LANL1DZ basis sets. Normal‐coordinate analyses were also performed with force fields determined from both the RHF/STO‐3G* and RHF/LANL1DZ basis sets. The calculated wavenumbers support the proposed vibrational assignment. These data are compared wit

ISSN:0377-0486    

DOI:10.1002/jrs.1250250905

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe optical and Raman spectra of several salts of croconic acid were investigated in order to obtain a better understanding of solid‐state effects. The results indicate that for the sodium and barium salts the perturbations can be ascribed to a decrease in the local symmetry of the anion. On the other hand, for the thallium and silver salts the perturbations are much more dramatic, clearly indicating the presence of charge‐transfer effects. For the silver salt, the abnormal enhancement in the Raman spectrum is ascribed to the presence of silver microparticles in the surface of the so

ISSN:0377-0486    

DOI:10.1002/jrs.1250250906

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

ISSN:0377-0486    

DOI:10.1002/jrs.1250250901

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY