Natural Bond Orbital (NBO) Population Study of Some Para-Substituted N-Methyl-N-nitrosobenzenesulfonamide Biological Molecules in MeCN Solution

A theoretical study of several para-substituted N-methyl-N-nitrosobenzenesulfonamide biological molecules in MeCN solution has been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with the 6-311++G(d,p) basis set. Geometries obtained from DFT calculations were used to perform natural bond orbital analysis. The results show that an intramolecular hydrogen bond exists in the selected molecules, which is confirmed by the NBO analysis. The p characters of the two nitrogen natural hybrid orbitals $ \sigma_{{{\text{N}}3 - {\text{N}}2}} $ increase with increasing $ \sigma_{p} $ values of the para-substituent group on the benzene ring, which results in a lengthening of the N₃–N₂ bond. It is noted that the weakness of the N–N bond is due to $ n_{{{\text{O}}1}} \to \sigma_{{{\text{N}}3 - {\text{N}}2}}^{*} $ delocalization and is responsible for the longer N₃–N₂ bond. In addition, there is a direct correlation between hyperconjugation $ n_{{{\text{O}}1}} \to \sigma_{{{\text{N}}3 - {\text{N}}2}}^{*} $ and the bond dissociation energy in the system, which is confirmed by comparison with isoelectronic isomers.