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Paper | Special issue | Vol 37, No. 3, 1994, pp.1473-1487
Published online, 1st January, 1970
DOI: 10.3987/COM-93-S54
A Computational Examination of the Anomeric Effect in 1,3-Diazanes

John T. Blair and John Stevens

*Technical Computations, 201-2S-05, 3M center, At. Paul, MN., U.S.A.

Abstract

The anomeric effect was examined for several 1,3-diazane molecules, with computations carried out at the HF/ 6-31G, HF/6-31G*, MP2-FC/6-31G*, and HF/6-311G** levels. Results were analyzed using the NBO method, and concepts of steric hindrance. The effect of n→σ* donation to C-N antibonds appears to control the conformation of diazane systems in which nitrogens are monosubstituted. The computed and experimental results show that specific n→σ* donation to C-N antibonds is irrelevant to the conformations of 1,3-diazane systems in which the nitrogens are trisubstituted. Lone pair electron repulsion would normally operate in the same sense as n→σ* donation. but extensive delocalization of the lone pairs in the σ orbitals appears to diminish this effect to insignificant levels. In the methyl substituted molecules, a generalized and subtle type of steric hindrance seems to be dominant over n→σ* electron donation in determining conformational preference.