RAMAN AND INFRARED-SPECTRA, CONFORMATIONAL STABILITY, VIBRATIONAL ASSIGNMENT AND AB-INITIO CALCULATIONS FOR ETHYL CHLOROFORMATE

Infrared (4000-50 cm(-1)) spectra of gaseous, amorphous and crystallin e solid ethyl chloroformate, ClCOOCH2CH3, and mid-infrared spectra (40 00-508 cm(-1)) of the chloroformate dissolved in liquefied krypton wer e recorded. Raman spectra of the liquid and solid phases were investig ated from 4000 to 50 cm(-1). MP2 and RHF ab initio calculations were c arried out using a 6-31G basis set. The calculations show that the co mpound can occur as the s-cis,trans, the s-cis,gauche, the s-trans,tra ns and the s-trans,gauche conformers. For each conformer the optimized structural parameters, the vibrational wavenumbers, infrared intensit ies, Raman scattering activities and potential energy distributions we re calculated. Both s-cis conformers were identified in the vibrationa l spectra of all non-crystalline phases. Evidence for the presence of the s-trans conformers is found in the liquid-phase Raman spectre. The enthalpy difference between the s-cis,ganche and s-cis,trans conforme rs was determined in the pure liquid phase to be 3.2 +/- 0.3 kJ mol(-1 ). Also in the liquid phase, the enthalpy difference between the obser ved s-trans and the s-cis,trans conformers was determined to be 14.3 /- 0.8 kJ mol(-1). Vibrational spectra of the crystalline solid, which contains only the s-cis,trans conformer, showed that ethyl chloroform ate can crystallize in two different forms. A complete assignment of t he infrared and Raman spectra is proposed.