RAMAN AND INFRARED SPECTRA, CONFORMATIONAL STABILITY AND {AB INITIO} CALCULATIONS OF {TRANS}-1-FLUORO-2-BUTENE

Abstract

The Raman (3200 to $10 cm^{-1}$) and infrared (3200to $20 cm^{-1}$) spectra of gaseous and solid {trans}-1-fluoro-2-butane, {trans}- $CH_{3}HC=CHCH_{2}F$, have been recorded. Additionally, the Raman spectrum of the liquid with qualitative depolarization data has also been obtained. Variable temperature studies have been carried out with the sample dissolved in xenon. These spectral data have been interpreted on the basis that the molecule exists in the fluid phases as a mixture of the synclinal (fluorine atom oriented {cis} to the double bond) and anticlinal ({gauche}) conformations . In the gaseous phase the synclinal conformer is more stable by $265 \pm 62cm^{-1} (758+ 177$ cal/mol) but in the liquid state the anticlinal conformer is more stable and the only conformer present in the solid state. {Ab initio} gradient calculations employing the $RHF/3-21G^{*}, RHF/6-31G^{*}$ and $MP2/6-31G^{*}$ basis sets predict the synclinal conformer to be more stable.