Isomerismo rotacional por ressonancia magnetica nuclear e calculos teoricos : [alfa]-haloacetatos de metila
AUTOR(ES)
Fabiana Yoshinaga
DATA DE PUBLICAÇÃO
2003
RESUMO
The present work reports the NMR and theoretical calculations of rotational isomerism in methyl a-haloacetates (halo = chlorine, bromine and iodine). The results were complemented with infrared spectroscopy. Ab initio calculations were performed with GAUSSIAN 98 program, using DFT/B3LYP and MP2 theories at different levels for the chlorine and bromine-derivatives. The geometries and the energies of the principal rotamers in methyl iodoacetate were calculated using the generator coordinated method with a LANL2DZ pseudopotencial. The H and C NMR spectra were obtained for all compounds in solvents of various polarities. The essential parameters for the solvation energy calculations were obtained through MODELS program using the optimized geometries in Gaussian. The best values of intrinsic coupling constants to each rotamer and the experimental energy difference in the vapour phase were obtained through BESTFIT program, using the experimental coupling constants. The experimental results and those from theoretical calculations show that the rotational isomerism in methyl a-haloacetates is between cis and gauche rotamers, however there is a notable difference in the stability and in the population of cis and gauche forms among the different methyl a-haloacetates.
ASSUNTO(S)
analise conformacional isomerismo
ACESSO AO ARTIGO
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