A DFT study of the Karplus-type dependence of vicinal 3J(Sn-C-X-C), X=N,O,S, in organotin (IV) compounds: application to conformationally flexible systems

ZORA relativistic and non-relativistic OFT protocols have been used to investigate vicinal coupling constants, (3)J(Sn-C-X-C), in several organotin(IV) compounds, with particular emphasis on cyclic alpha-aminoorganostannanes. The dependence of the coupling constant on the heteroatom X (X = N,O,S) in the coupling path, and, for X = N. its substituents, has been studied in detail. The electron-withdrawing strength of the N-substituents has been found to strongly affect the magnitude and shape of the Karplus-type curve. The results obtained for the simple model systems, having no or little conformational flexibility, have helped in rationalizing the data concerning real flexible cyclic systems recently investigated in the literature. For these intricate cases a population analysis of various conformers has allowed to obtain a very good agreement between calculated and experimental data. It is therefore established that NMR J couplings, together with OFT calculations, are a very useful tool to investigate conformational issues in solution by comparison of experimental and weighted average calculated values.