CONFORMATIONAL STUDIES OF CYCLOPROPYLMETHYL ACETYLENE FROM TEMPERATURE DEPENDENT FT-IR SPECTRA OF XENON SOLUTIONS. INFRARED AND RAMAN SPECTRA, AND AB INITIO CALCULATIONS
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Date
1998
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Publisher
Ohio State University
Abstract
Variable temperature $(-55 to -100^{\circ}C)$ studies of the infrared spectra (3500 to $400 cm^{-1})$ of cyclopropylmethyl acetylene, $c-C_{3}H_{5}CH_{2}CCH$, dissolved in liquid xenon have been caried out. Utilizing three different sets of conformer bands, an enthalpy difference of $128 \pm 14 cm^{-1} (1.53 \pm 0.05 kJ/mol)$ was obtained with the cis (acetylenic group over the three-membered ring) from the more stable conformer. A complete vibrational assignment is proposed for the cis conformer and several of the fundamentals for the gauche conformer have been identified. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force constants. However, the gauche conformer remains in the infrared and Raman spectra of the solid. The calculations were carried out at the restricted Hartree-Fock (RHF) level or with electron correlation to second order (MP2), utilizing four different basis sets. The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies have been obtained for both conformers. The results will be discussed and compared to the corresponding quantities for some similar molecules such as cyanomethylcyclopropane and the halomethylcyclopropanes.
Description
Author Institution: Department of Chemistry, University of Missouri-Kansas City