EFFECT OF THE AMINE GROUP ON RELATIVE BOND STRENGTHS IN CUBANE AND AZACUBANES
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abstract
We have carried out an ab initio self-consistent-field molecular orbital study of the structures and relative bond strengths of some monoamine derivatives of cubane, azacubane, and 1,3-diazacubane. Our focus has been on the effect of the NH2 group on the strengths of the endocyclic strained bonds in these molecules, and, in particular, on the conformation dependence of this effect. Our results show a consistent bond-weakening observed in one [and only one] C-C or C-N bond adjacent to the site of NH2 substitution. We find that the particular bond that is weakened is in all cases essentially coplanar with the C-NH2 bond and the position of the most negative electrostatic potential of the amine nitrogen. This direction-specific bond-weakening is viewed as an example of the anomeric effect. 1991 VCH Publishers, Inc.