CONFORMATIONAL STABILITY FROM TEMPERATURE DEPENDENT FT-IR SPECTRA OF LIQUID RARE GAS SOLUTIONS AND AB INITIO CALCULATIONS FOR 1-PENTYNE
Loading...
Date
2000
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
Variable temperature studies of the infrared spectra (3500 to $400 cm^{-1}$) of 1-pentyne, $CH_{3}CH_{2}CH_{2}CCH$, dissolved in liquid xenon ($-55$ to $- 100^{\circ} C$) and liquid krypton (-105 to $-150^{\circ} C$) have been recorded. These date indicate that both the anti (methyl group trans to the acetylenic group) and gauche conformers are present in the fluid states, Utilizing seven sets of conformer pairs for the xenon solution and ten sets of conformer pairs for the krypton solution, the enthalpy has been determined to be $50\pm 6 cm^{-1} (0.60 \pm 0.07 kJ/mol$) and $45 \pm 4 cm^{-1} (0.54 \pm 0.05 kJ/mol$), respectively, with the anti conformer the more stable form. Optimized geometries and conformational stabilities were obtained from ab initio MP2/6- 31G(d), MP2/6-311+G(d, p), MP2/6-311+G(2d, 2p) and MP2/6-311+G(2df, 2pd) calculations with all of the calculations predicting the gauche rotamer to be the more stable form. The $r_{o}$ adjusted structural parameters have been obtained from a combination of the microwave rotational constants and ab initio predicted parameters.
Description
Author Institution: Department of Chemistry, University of Missouri-Kansas City