VIBRATIONAL-SPECTRA AND CONFORMATIONAL STABILITY OF NORMAL-BUTANE - COMMENT

A study of the vibrational spectrum of gaseous n-butane was recently presented in this journal [J. R. Durig et al., J. Raman Spectrosc. 22, 683 (1991)]. From the temperature dependence of the Raman spectrum, the enthalpy difference between the trans and gauche conformers was found to be ca 375 cm-1 (1072 cal mol-1). In a recent absolute intensity study of gaseous n-butane [W. F. Murphy et al., J. Phys. Chem. 95, 1124 (1991)], a relative conformer abundance was determined which corresponds to an energy difference of 690 cal mol-1 (241 cm-1). The latter result confirms several other recent determinations of this quantity. Concerns regarding the validity of the temperature dependence method are presented, and the preference for the lower value of the enthalpy difference is defended.