DONOR-ACCEPTOR (PUSH-PULL) ETHANES - POSSIBLE BOND-STRETCH ISOMERS OF1,1,1-TRIAMINO-2,2,2-TRICYANOETHANE AND 1,1,1-TRIAMINO-2,2,2-TRINITROETHANE

Previous work has shown that Limited basis set self-consistent field c alculations on the title compounds yield structures with two stable mi nima. One minimum corresponds to a covalent isomer while the second mi nimum corresponds to an ionic one. In this work, we show that even wit h larger basis sets and perturbation corrections for electron correlat ion two minima are still apparent. Since frequency calculations produc ed only real frequencies for both minima for the tricyano molecules an d produced only a pair of imaginary frequencies corresponding to a deg enerate set of rotations for the trinitro molecules, it was concluded that both stationary points on each potential surface are true minima. The minima corresponding to the ionic isomers are much more stable th an the ones corresponding to the covalent isomers, which are barely bo und with respect to the barrier separating them. Thus, the latter coul d be detected only spectroscopically if at all. The structure of sever al other possible isomers and dimer were also investigated. These calc ulations suggest that the solid material will be mainly ionic with a n etwork of hydrogen bonds.