Please use this identifier to cite or link to this item: http://repositorio.unicamp.br/jspui/handle/REPOSIP/56496
Type: Artigo de periódico
Title: Conformational analysis .27. NMR, solvation and theoretical investigation of conformational isomerism in fluoro- and 1,1-difluoro-acetone
Author: Abraham, RJ
Jones, AD
Warne, MA
Rittner, R
Tormena, CF
Abstract: The solvent and temperature dependence of the H-1 and C-13 NMR spectra of fluoroacetone (FA), 1,1-difluoroacetone (DFA) and 1,1,1-trifluoroacetone (TFA) are reported and the (4)J(HF), (1)J(CF) and (2)J(CF) couplings analysed using ab initio calculations and solvation theory. In FA the energy difference (E(cis) - E(tr)) between the cis (F-C-C=O 0 degrees) and trans (F-C-C=O 180 degrees) conformers is 2.2 kcal mol(-1) in the vapour, decreasing to 1.0 kcal mol(-1) in CCl4 solution and to -0.6 kcal mol(-1) in the pure liquid. In DFA the conformational equilibrium is between the less polar cis (H-C-C=O 0 degrees) and a gauche conformation (H-C-C=O 104 degrees). The energy difference (E(g) - E(cis)) is +0.8 kcal mol(-1) in the vapour, decreasing to 0.1 kcal mol(-1) in CCl4 solution and to -0.6 kcal mol(-1) in the pure liquid. The vapour state energy difference for FA compares well with that calculated (2.8 kcal mol(-1) at MP4/6-31G*). DFA calculations at this level gave only one minimum in the potential surface corresponding to the cis form, A minimum for the gauche conformer was only found when sol solvation was included in the ab initio calculations, or at much larger basis sets (6-311++G**). The conformer couplings obtained show that the (4)J(HF) coupling (F-C-C-CH3) is proportional to cos(2) theta, where theta is the F-C-C-C dihedral angle. The (1)J(CF) and (2)J(CF) couplings also show a pronounced orientation dependence which could be of particular utility in those cases where other couplings are not present.
Country: Inglaterra
Editor: Royal Soc Chemistry
Rights: aberto
Identifier DOI: 10.1039/p29960000533
Date Issue: 1996
Appears in Collections:Artigos e Materiais de Revistas Científicas - Unicamp

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