Isomerism and adduct formation in the Hector''s base series: A MNDO study of model compounds

MNDO calculations on a series of a model compounds show that the observed structures for Hector's base, Dost's base and Dost's keto compound are the thermodynamically most stable tautomers and that the bond-switched structure observed for the 1:1 adduct of Hector's base with carbon disulphide and the non-bond-switched structure observed for the corresponding adducts with isocyanates and isothiocyanates are both the thermodynamically most favoured isomers, so that the occurrence or otherwise of a bond switch in these compounds is determined by thermodynamic rather than by mechanistic factors. Proposed mechanisms for the formation of the carbon disulphide adduct of Hector's base, and for its desulphurisation are supported by MNDO calculations.