The equilibrium geometries and electronic structures of >20 intermediates of the Mannich reaction, N-hydroxymethyl amines and methylene amine carbenium ions, have been optimized and calculated by the MNDO method. The feasibility of elimination of water, the stability of methylene amine carbenium ions, and the effect on the mechanism of the Mannich reaction are discussed. The mechanism of Mannich reactions of OC(NH2)2, HCHO, and HO(NO2)3 was suggested as a example of multiple N-hydroxymethylation. The N-hydroxymethyl amines and corresponding methylene amine carbenium ions for nitrourea have been also calculated and discussed.

Key words: STABILITY, REACTION MECHANISM, ELECTRONIC STRUCTURE, DEHYDRATION REACTION, MANNICH REACTION, UREAS, MOLECULAR ORBITAL METHOD, OPTIMIZATION, METHYLOLATION