Hydride-donation reaction of reduced nicotinamide adenine dinucleotide. 1. MINDO/3 and STO-3G calculations on analog reactions with cyclopropene, tropylidene, and 1,4-dihydropyridine as hydride donors and the cyclopropenium cation as acceptor

On the basis of MO arguments it is made plausible that the hydride-transfer reactions are valid and useful analogues of the NAD+/NADH hydride-transfer reaction. By means of MIND0/3-enthalpy contour maps a suitable reaction coordinate is found for each reaction. For the simplest system cyclopropene/cyclopropenium cation, the enthalpy profile along the reaction coordinate is compared with ab initio (STO-3G) results. It is demonstrated that both methods produce very similar results with regard to the overall course of the reaction (the reaction pathway), but that MIND0/3 yields a much lower activation enthalpy than STO-3G. The results indicate that the studied hydride-transfer reactions can all be conveniently described with reference to a supermolecule of C, symmetry, containing a linear C-.H.-C fragment. The reaction consists of a concerted and gradual breaking of one, and forming of the other one of the C-H bonds in this fragment. Simultaneously transfer of negative charge takes place, the overall result being the migration of a hydride ion