Towards a complete description of the reaction mechanisms between nitrenium ions and water

Abstract

Context

Nitrenium ions are intermediates in the metabolic routes producing the highly carcinogenic nitrosamines and binding to DNA molecules. The reaction mechanism of nitrenium molecules with explicit water molecules is sensibly dependent on the number of waters: when a second molecule is involved, it acts as a catalyst for the reaction, lowering intrinsic activation barriers regardless of the substituent. For all cases, the reaction force constants and reaction electron flux indicate highly synchronous reactions for \({n=1}\). Conversely, for \({n=2}\) highly non-synchronous reactions are obtained, involving two separate proton transfers happening early and late in the reaction path. As a test case, for the simplest \([\text {N}\text {H}_{2}]^{+} + 2 \text {H}_{2}\text {O}\) reactions, orbital interactions within the NBO paradigm, bond orders, and their derivatives indicate that each individual proton transfer is highly synchronous.

Methods

Molecular geometries were optimized and characterized at the B3LYP/6–311++G(d, p) level. Intrinsic reaction coordinates were calculated. CCSD(T) single point energies with the same basis were computed on all stationary points. The reaction force, reaction force constant, and reaction electron flux are used to study the evolution of the reacting systems. Natural bond orbitals are used to understand the primitive changes driving the reaction.