CONFORMATIONAL STABILITY AND STRUCTURAL PARAMETERS OF CH3CH2CCLO AND OTHER (CH3)(N)CH3-NCCLO MOLECULES

Variable temperature (-60 to -100 degrees C) studies of the infrared s pectra (3500 to 400 cm(-1)) of propionyl chloride, CH3CH2CClO, dissolv ed in liquid xenon have been recorded. From these data the enthalpy di fference between the rotational isomers has been determined to be 505 +/- 32 cm(-1) (1.44 +/- 0.09 kcal mol(-1)) with the trans conformer (m ethyl group eclipsing the oxygen atom) more stable than the gauche for m. From this Delta H value, along with assigned torsional fundamentals for both conformers and accompanying ''hot bands'', the potential fun ction governing the conformational interchange was calculated. Utilizi ng the infrared data from the xenon solution, along with some new Rama n data and ab initio frequency predictions from MP2/6-31G* calculation s, a few reassignments of the fundamentals have been made. Ab initio c alculations were carried out with several different basis sets up to M P2/6-311G** from which structural parameters and conformational stabil ities were determined. These parameters are compared to those obtained from earlier microwave and electron diffraction data. Similar ab init io calculations have been carried out for CH3CClO, (CH3)(2)CHCClO and (CH3)(3)CClO and these results are compared to the corresponding exper imental results where appropriate. (C) 1998 Elsevier Science B.V.