Probing the anomeric effect. The diaminomethylene group: Calculations of NCN‐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 (H 2 NCH 2 NH 2 ) 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.