Long distance electronic effects of para-substituted beta-nitrostyrenes byC-13-NMR spectroscopy

By means of C-13-NMR spectroscopy and AM1 molecular orbital calculations of para-beta-nitrostyrenes, we have found a characteristic long distance char ge transfer pattern, where the olefinic bridge (CH=CH) and the aromatic rin g (Ph) carbon centres are perturbed according to the donor-nature of the pa ra-substituent groups. After a complete spectral assignment of the C-13-NMR signals, the chemical shifts (delta) of the C-1, C-3 and C-beta centres sh ow a linear functional dependence with the charge densities (q(AM1)), while in the same molecular series C-2 and C-alpha are practically constants. On the other hand, an analysis of the electron-donor substituent effect at th e para-position of the aromatic carbonyl compounds on the C-4 centre, has p ermitted us to find a good correlation between the C-4 chemical shift and t he electronegativity of this vicinal centre. (C) 1999 Elsevier Science B.V. All rights reserved.