Charge at the migrating hydrogen in the transition state of hydride transfer reactions from CH groups to hydride acceptors. Dynamics of the redox‐couple NADH‐NAD+

We consider the controversial conclusions of the charge at the migrating hydrogen in the transition state of hydride‐transfer reactions from CH‐groups to hydride acceptors. Quantum chemical calculations were performed on elementary organic reactions involving carbenium ions, which can be considered as hydride acceptors. We also discuss the biochemical hydride‐transfer reactions in which the coenzyme NADH‐NAD+ plays an important role. With the calculations and the experimental model systems, an answer is given for the stereospecificity of the hydride transfer. Generally, the hydride transfer occurs via a trigonal pyramidal geometry in which the transferred hydride of the CH‐group is located in the axial position. In the case of the coenzyme NADH‐NAD+, the hydride transfer is coupled with an out‐of‐plane orientation of the carboxamide group of the pyridinium moiety, resulting in an increased stereospecificity.