Conformational and structural studies of ethynylcyclopentane from temperature dependent Raman spectra of xenon solutions, infrared spectra, and ab initio calculations

Variable temperature (-50 to -100 degrees C) Raman spectra (3500-136 cm(-1)) were recorded of ethynylcyclopentane, c-C5H9CCH in liquid xenon. The envelope-equatorial (Eq) conformer was determined more stable than envelope-axial (Ax) form with enthalpy difference of 94 +/- 9 cm(-1) (1.12 +/- 0.11 kJ/mol) and 39 +/- 2% Ax conformer present at ambient temperature. The conformational stabilities have been predicted from ab initio calculations with basis sets up to aug-cc-pVTZ. From previously reported microwave rotational constants and ab initio Mp2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters are reported Eq [Ax] distances (angstrom) rC=C = 1.211(3) [1.211(3)], rC(alpha)-C C = 1.461(3) [1.467(3)], rC(alpha)-C-beta = 1.542(3) [1.542(3)], rC(beta)-C-gamma = 1.541(3)[1.542(3)], rC(gamma)-C-y' = 1.556(3)[1.555(3)] and angles (degrees) angle C alpha-C C = 179.4(5) [179.9(5)], angle C beta C alpha-C C = 113.7(5) [111.5(5)], angle C beta C alpha C beta' = 102.6(5) [102.1(5)], angle C alpha C beta C gamma = 103.7(5) [103.7(5)], angle C beta C gamma C gamma' = 106.0(5) [105.9(5)] and tau C beta C alpha C beta'C gamma' = 40.8(5) [41.6(5)]. Vibrational assignments are reported, supported by ab initio predictions and results are discussed. (C) 2013 Elsevier B.V. All rights reserved.

Jaar van publicatie:2013