Conformational preference of nitroformazans: A computational study

A conformation analysis of all possible isomers of 22 differently substituted 1,5-bis(phenyl)-3-nitroformazans is presented. Results clearly showed that, except for 1,5-bis(m-OPh-phenyl)-3-nitroformazan, the closed ring trans-syn, s-cis isomer (DD) is preferred. This result agrees with available experimental structures of differently substituted 1,5-bis(phenyl)-3-nitroformazans that all exhibit the closed ring trans-syn, s-cis conformation. The preference for the closed ring trans-syn, s-cis conformation was further explored by natural bond orbital and quantum theory of atoms in molecules analysis. It was hereby shown that the donor-acceptor interaction and electron density of the bond path related to the intramolecular N–HN hydrogen bond in the closed ring trans-syn, s-cis isomer (DD) is stronger and larger respectively than in other isomeric forms such as the open trans-syn, s-trans (UD and DU) and linear trans-anti, s-trans (UU) configurations. © 2019 Elsevier B.V.