Quang Ton That, K. Nguyen, P. Hansen
Apr 1, 2005
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Journal
Magnetic Resonance in Chemistry
Abstract
Schiff bases of gossypol with benzylamine, methylamine, 4‐aminoacetophenone and 4‐fluoroaniline have been synthesized and characterized by NMR spectroscopy. All the Schiff bases of gossypol are in the enamine form according to 3J(HC,NH) and 1J(N,H) coupling constants. The spectra are basically unchanged by change of solvent (CD2Cl2, THF‐d8 and CD3OD) and by variation of temperature. For the derivative of benzylamine, deuterium isotope effects on 13C chemical shifts are determined. They support strongly the enamine form and serve as a reference for other tautomeric Schiff bases. Structures and NMR nuclear shieldings of model compounds (the second monomer is replaced by a 2‐hydroxybenzene ring) have been calculated by density functional theory (DFT) methods. A good correlation is observed between calculated 13C nuclear shieldings of the enamine form and observed 13C chemical shifts. Copyright © 2005 John Wiley & Sons, Ltd.