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Conformational, vibrational, and structural studies of 2,2,3,3,3‐pentafluoropropylamine from Raman and infrared spectra of gas, liquid, xenon solutions, and solid supported by ab initio calculations
Author(s) -
Guirgis, Gamil A.,
Darkhalil, Ikhlas D.,
Klaassen, Joshua J.,
Ganguly, Arindam,
Wyatt, Justin K.,
Durig James R.
Publication year - 2012
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.2993
Subject(s) - conformational isomerism , isotopomers , raman spectroscopy , chemistry , xenon , ab initio , ab initio quantum chemistry methods , dihedral angle , enthalpy , infrared , infrared spectroscopy , density functional theory , analytical chemistry (journal) , crystallography , computational chemistry , molecule , hydrogen bond , thermodynamics , organic chemistry , physics , optics
The Raman and infrared spectra (3500–50 cm −1 ) of the gas, liquid or solution, and solid were recorded of 2,2,3,3,3‐pentafluoropropylamine (CF 3 CF 2 CH 2 NH 2 ) and the ND 2 isotopomer. Variable temperature (−55 to − 100 °C) studies of the infrared spectra (3600–400 cm −1 ) of samples dissolved in liquid xenon have been carried out. From these data, two of the five possible conformers have been identified and their relative stabilities obtained. The enthalpy difference was determined between the more stable Tt conformer and the less stable Tg form to be 280 ± 14 cm −1 (3.35 ± 0.17 kJ/mol). The first indicator is the NCCC dihedral angle ( G = gauche or T = trans ), and the second one ( g = gauche or t = trans ) is the relative position of the lone pair of electrons on nitrogen with respect to the β‐carbon. The percentage of the Tg conformer at ambient temperature is estimated to be 34 ± 2%. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug‐cc‐pVTZ for both MP2(full) and density functional theory calculations by the B3LYP method. Vibrational assignments have been provided for most of the observed bands for both isotopomers, supported by MP2(full)/6‐31G(d) ab initio calculations to predict the harmonic force fields, wavenumbers, infrared intensities, Raman activities, and depolarization ratios for both conformers. Estimated r 0 structural parameters were obtained from adjusted MP2(full)/6‐311 + G(d,p) calculations. The results are discussed and compared with the corresponding properties of some related molecules. Copyright © 2011 John Wiley & Sons, Ltd.