Computational analysis of the dinitramine and chlorine derivatives of benzene and s-tetrazine

Abstract

Optimized HF/3-21G ∗ geometries were computed for s-tetrazine (I) and for the dinitramine and chlorine derivatives of I and of benzene. These structures were used to calculate the electrostatic potentials and average local ionization energies of these molecules. HF/3-21G ∗ and MP2/6-31G ∗ geometries were also computed for pentazine ( VI), which is as yet unknown, and shown to correspond to energy minima. The electrostatic potential on the surface of I is strongly negative above the electron-attracting ring nitrogen atoms and positive above the ring and the hydrogen atoms, fully consistent with the structures of complexes that s-tetrazine is known to form with other molecules. Previously developed relationships were used to estimate the Hammett constants σ m and σ p of the dinitramine group, N(NO 2) 2, and the p K a values of s-tetrazine, its dinitramine and chlorine derivatives, and pentazine. N(NO 2) 2 is found to be strongly electron withdrawing through induction and more weakly donating through resonance. In the s-tetrazine derivatives, the electron attracting power of the ring nitrogen atoms significantly increases the extents of conjugation of the N(NO 2) 2 and Cl, both resonance donors. However, the dominant effect of these substituents upon the ring is inductive deactivation toward electrophiles.