Estudos de RMN de 1H e de 13C de derivados da 1,7,7-trimetilbiciclo [2.2.1] heptano-2-ona 3-substituida

AUTOR(ES)
DATA DE PUBLICAÇÃO

1992

RESUMO

This work aimed to evaluate the empirical substituents effects on the Carbon-13 chemical shifts of 3-substituted 1,7,7 -trimethylbicyclo[2.2.1]heptan-2-one derivatives (or 3-substituted camphor) and their contingent dependence on electronic and steric transmission mechanisms. A literature survey had shown that, besides other things, there was controversy on the attribuition of some hydrogens and carbons signals of H and C NMR for the basic molecule. In this way a discerning attribuition was made for the Hydrogen-1 and Carbon-13 Spectra signals, as much for camphor as for the other substituted compounds, by means of high-field NMR multiple pulse technics, in one (1D) and, mainly, in two dimensions (2D). The compounds were synthesized by procedures described in the literature or, in most instances, adaptation of these. Almost alI the epimeric mixtures obtained in these synthesis were separated by Preparative High Performance Liquid Chromatography (HPLCP). The camphor 3-substituted (RZ) derivatives, that were not yet described are: Z = F (endo); I (endo and exo); OMe (endo and exo); SMe (exo); NHMe (exo). The others: Z = F (exo); SMe (endo); NHMe (endo); NMe2 (endo); CI (endo and exo); Br (endo and exo); OH (enda and exo); CH3 (endo and exo); 3,3-dichlorocamphor; 2,3-bornanedione and camphor trimethylsililenolether, had already been described in the literature. Based on the unequivocal assignments of Carbon-13 signals, the empirical substituent effects were determined, through the carbon chemical shifts difference between the 15 monossubstituted derivatives and the basic molecule (camphor), to confrontation with the steric and electronic substituent parameters, by simple linear regression analysis. The data of the a and b (on the carbonyl) effects have showed good correlations with the inductive and electric-field parameters, respectively. ln both cases, it was observed that the empirical effects magnitudes are apreciably smaller than that of analogous monosubstituted bicycloalkanes, what was attributed to nonadditivity effects NAE, due, likely, to electronic interactions between C-Z and C = O groups. Good correlations were aIso obtained for the g-gauche and d-syn-axial effects with steric effect parameters. AIthough these correlations denote, for both, the same transmission rnechanisrn, the empirical effects show a diametricaly opposite tendency, namely, shielding for g-gauche anel deshielding for d-syn-axial. Even though the inductive and the steric effect parameters have shown partial interdependence, a great number of the correIations with the empirical effects were in agreement with the literature propositions for the transmission mechanism.

ASSUNTO(S)

ressonancia magnetica nuclear quimica organica

ACESSO AO ARTIGO

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