Balancing Steric and Electronic Factors in Push-Pull Benzenes: An ab Initio Study on the Molecular Structure of 1,3,5-Triamino-2,4,6-trinitrobenzene and Related Compounds

Abstract

The structures of 1,3,5-triamino-2,4,6-trinitrobenzene (2) and related compounds (3–5) are studied using ab initio Hartree-Fock (6-31G(D)) and local density functional (LDF) computational methods. In contradiction to published structures for 2 predicted from semiempirical data, both ab initio methods predict a planar structure in accord with the experimental X-ray crystallographic study. It is concluded that appreciable “push-pull” conjugation is present in 2 and that the interaction between flanking groups is mainly attractive through cyclic hydrogen bonding. Computations on 3–5 were used to gauge the affinity for some rings to distort into boat instead of chair forms. The relative electron density distributions for 2 and 5 are discussed. The planar forms of 2 and 5 are shown to support the concept that static “gear clashing” in combination with push-pull effects are responsible for the warped structure of alkyl substituted cognates of 2. © 1993, American Chemical Society. All rights reserved.