Abstract
The conformational behaviour of Ar 2CH(CN)CH(Ar 1)CH 2COR (R OCH 3; N(CH 3) 2; Ar 1 Ph; Ar 2 Ph or 1-naphthyl) has been investigated by 1H and 13C NMR spectroscopy. The vicinal proton-proton coupling constants were used together with those of carbon-proton couplings to provide information on the conformational preference in the compounds studied. The conformational distribution with respect to the C(2)C(3) bond is shifted to the conformation having trans Ph and COR groups. Coupling constants involving the cyano carbon atom and the methine proton are J g CN,H = 2.0 Hz and J t CN,H = 14.1 Hz. The conformation with the cyano group and the methine proton trans to each other, with gauche-oriented protons around the C(3)C(4) bond is the preferred one for both isomers in the compounds investigated. The results obtained support the assumption that electrostatic (non-bonded attractive) interactions rather than steric demands operate as dominant factors in controlling the conformational equilibrium.
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