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|Type:||Artigo de periódico|
|Title:||Conformational Analysis. Part 33. An Nmr, Solvation And Theoretical Investigation Of Conformational Isomerism In N,n-dimethylfluoroacetamide And N,n-dimethyl-α-fluoropropionamide|
|Abstract:||The solvent and temperature dependence of the 1H and 13C NMR spectra of N,N-dimethylfluoroacetamide (DMFA) and N,N-dimethyl-α-fluoropropionamide (DMFP) are reported and the 5JCF, 1JCF and 4JCF couplings analysed by solvation theory. Density function theory (DFT) at the B3LYP/6-311 +G(d,p) level with ZPE (zero point energy) corrections was used to obtain the conformer geometries. In DMFA, the DFT method gave only two minima for the cis (F-C-C=O, 0°) and gauche (F-C-C=O, 140.6°) rotamers. The trans rotamer was not a minimum in the energy surface. Assuming only the cis and gauche forms, the observed couplings when analysed by solvation theory gave the energy difference (Ecis - Eg) of 2.5 kcal mol-1 in the vapour phase, (cf. the ab initio value of 2.3 kcal mol-1) decreasing to 0.87 kcal mol-1 in CCl4 and to -1.29 kcal mol-1 in DMSO. In DMFP the ab initio calculations gave three minima; the cis (F-C-C=O, 30.4°), gauche-1 (F-C-C=O, 144.7°) and gauche-2 (F-C-C=O, -124.1°) rotamers with (Ecis - Eg2) equal to 2.5 kcal mol-1 and (Eg1 - Eg2) equal to 0.3 kcal mol-1. The observed couplings were analysed by solvation theory assuming one "average" gauche conformer to give (Ecis - Eg(AV)) equal to 2.1 kcal mol-1 in the vapour phase, decreasing to 0.83 kcal mol-1 in CCl4 and to -1.11 kcal mol-1 in DMSO.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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