CONFORMATIONAL STUDIES OF CYCLOPROPYLCARBONYL CHLORIDE FROM TEMPERATURE-DEPENDENT FT-IR SPECTRA OF XENON SOLUTIONS

Variable temperature (-60 to -100 degrees C) studies of the infrared s pectra (3500 to 400 cm(-1)) of cyclopropylcarbonyl chloride, c-C3H5CCl O, dissolved in liquid xenon have been recorded. Utilizing several dou blets due to the cis and trans conformers, the enthalpy difference has been determined to be 102 +/- 19 cm(-1) (292 +/- 54 cal mol(-1)), wit h the cis conformer (oxygen atom cis to the three-membered ring) the m ore stable rotamer. From this Delta H value, along with assigned torsi onal transitions of 87.4 and 54.7 cm(-1) for the trans and cis conform ers, respectively, and with excited state transitions for torsional mo des for both conformers, the potential function governing the conforma tional interchange has been calculated. The cis-to-trans barrier has b een determined to be 2180 +/- 100 cm(-1) (6.23 +/- 0.29 kcal mol(-1)). Utilizing the new infrared data from the xenon solution, along. with some additional Raman data, and ab initio predictions from MP2/6-31G calculations, several reassignments of the fundamentals have been made . Ab initio calculations have been carried out with several different basis sets up to MP2/6-311++G*, from which structural parameters and conformational stabilities have been determined. Irrespective of the s ize of the basis sets, the cis conformer is predicted to be the more s table conformer, which is consistent with the experimental results. Th e spectroscopic and theoretical results are compared to the correspond ing quantities for some similar molecules. (C) 1997 Elsevier Science B .V.