COMPUTATIONAL DETERMINATION OF THE STRUCTURES AND SOME PROPERTIES OF TETRAHEDRANE, PRISMANE, AND SOME OF THEIR AZA ANALOGS
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We have carried out an ab initio self-consistent field computational study of tetrahedrane, prismane, and nine of their aza analogues, in which C-H units have been replaced by nitrogens. Structures optimized at the 3-21G level were used to compute molecular electrostatic potentials, as guides to reactive behavior, and bond deviation indexes as quantitative indicators of bond strain. Within each set of azaprismane isomers, the most stable is the one having the fewest N-N bonds. The exceptional length of these bonds, approximately 1.59 , may reflect a tendency to rupture. In the tetrahedranes, the bonds are quite highly strained but become less so as the number of nitrogens increases. The degrees of bond strain are not as great in the prismanes and do not necessarily diminish as more nitrogens are introduced. There are negative electrostatic potentials associated wtih the C-C bonds in tetrahedrane and prismane, indicating that these bonds can serve as initial sites for electrophilic attack. These potentials are greatly weakened or eliminated by the introduction of nitrogens. In the azatetrahedranes and azaprismanes, there are strong and extensive negative regions near the nitrogens, suggesting significant basicity; these also become weaker as the number of nitrogens increases. 1989 American Chemical Society.
