Estudos de ressonancia magnetica nuclear de 2-metilpropenos 3-substituidos

AUTOR(ES)

Mara Elisa Fortes Braibante

DATA DE PUBLICAÇÃO

1987

RESUMO

The aim of the present work has been the investigation of the substituent effects in the Carbon-13 and Hydrogen-1 chemical shifts of some 3-substituted 2-methylpropenes ( I ), which bear a closely related geometry to a -substitued propanones. The following compounds (I) have been obtained in good yields. through usual methods where changes were introduced either to improve the yields or to prepare unknown derivatives. Attempts to obtain the 3-fluor and the 3-cyano-2-methylpropene were unsucessful. The interpretation of the substituent effects in the Carbon-13 n.m.r. chemical shifts were performed on the grounds of the usual concepts of Physical Organic Chemistry, through empirical correlations with substituents eletronic and steric effects and also with substituents empirical effects. Empirical calculations for the a-methylene carbon chemical shift, through a Grant and Paul relationship have shown deviations for some substituents (Z= halogens - and oxygen bearing group). Roberts method has been applied to estimate the chemical shifts of the olefinic carbons. The b and b parameters and the a a ,aa, ab and a b interaction terms were determined. The olefinic carbons calculated chemical shift were in close agreement with the experimental values. The Hydrogen-1 n.m.r. spectra were also fully analyzed. The olefinic protons signals were assigned and the couplings constants measured. The nuclear Overhauser effect and the lanthanide induced shifts allowed the protons chemical shifts assignments. The JHH cisoid and transoid coupling constants were carefully measured and their values were used for the spectra simulation to make sure the chemical shifts were correctly assigned. MNDO, (Modified neglect of diatomic overlap) molecular orbital calculation were performed for the Oxygen bearing compounds (3, 11 and 12 ) yielding the net charge and eletronic charge densities as well as data for the molecular geometry of these compounds. Data tables were included in the Appendix.

ASSUNTO(S)

analise espectral ressonancia magnetica nuclear

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