RAMAN AND INFRARED-SPECTRA, CONFORMATIONAL-ANALYSIS, AB-INITIO CALCULATIONS AND VIBRATIONAL ASSIGNMENT OF 3-BROMOPROPIONITRILE

The Raman (3200-10 cm(-1)) and infrared (3100-400 cm(-1)) spectra were recorded for liquid and solid 3-bromopropionitrile, BrCH2CH2CN. These data are interpreted on the basis that the molecule exists as a mixtu re of trans (Br atom oriented trans to the CN group) and gauche confor mers in the liquid phase with the gauche form the more stable rotamer and the only conformer in the solid. From variable-temperature Raman s tudies of the liquid, the enthalpy difference between conformers was d etermined to be 434 +/- 19 cm(-1) [(1.24 +/- 0.05 kcal mol(-1)) (1 kca l = 4.184 kJ)]. A complete vibrational assignment is proposed for both conformers. Ab initio calculations were performed employing the RHF/L ANL1DZ basis set to obtain the structural parameters, barriers to inte rnal rotation, the fundamental wavenumbers for both conformers and the infrared and Raman intensities. The calculated values are compared wi th the corresponding experimental quantities. These results are discus sed and compared with similar quantities obtained for some related mol ecules.