Conformational stability and structural parameters of CH3CH2CClO and other (CH3)nCH3-nCClO molecules

Variable temperature (-60 to -100 degrees C) studies of the infrared spectra (3500 to 400 cm(-1)) of propionyl chloride, CH3CH2CClO, dissolved in liquid xenon have been recorded. From these data the enthalpy difference between the rotational isomers has been determined to be 505 +/- 32 cm(-1) (1.44 +/- 0.09 kcal mol(-1)) with the trans conformer (methyl group eclipsing the oxygen atom) more stable than the gauche form. From this Delta H value, along with assigned torsional fundamentals for both conformers and accompanying ''hot bands'', the potential function governing the conformational interchange was calculated. Utilizing the infrared data from the xenon solution, along with some new Raman data and ab initio frequency predictions from MP2/6-31G* calculations, a few reassignments of the fundamentals have been made. Ab initio calculations were carried out with several different basis sets up to MP2/6-311G** from which structural parameters and conformational stabilities were determined. These parameters are compared to those obtained from earlier microwave and electron diffraction data. Similar ab initio calculations have been carried out for CH3CClO, (CH3)(2)CHCClO and (CH3)(3)CClO and these results are compared to the corresponding experimental results where appropriate. (C) 1998 Elsevier Science B.V.