Probing the anomeric effect. The diaminomethylene group: Calculations of NCN‐containing molecular systems¹

A study of systems containing the title moiety is described, with special reference to the anomeric effect. We have calculated ab initio, using Gaussian‐80 with the 3‐21G basis set, all basic conformations of methylene‐diamine (H₂NCH₂NH₂) and its N‐methyl derivative with full geometry optimization of energy minima and barriers. The structural data thus obtained, were then employed to parameterize Allinger's MM2‐80 force field in a procedure similar to that described for oxygen derivatives, including hydrogen‐bonding effects and CN bond shortening in tertiary amines. This modification, termed MM2‐AE was then used to calculate larger molecules, including N,N′‐di‐ and N,N,N′,N′‐tetramethyl‐methylenediamine, various 1,3‐diazane systems, and 1,4,5,8‐tetraazadecalin derivatives of established (x‐ray) structures. The results are discussed in light of their verificative and predictive power and appear to validate MM2‐AE as a useful computational procedure.