Bending effect on the stabilities of quadruple hydrogen bonding systems: theoretical study of a series of self-constituted quadruple hydrogen bonded complexes (C9H9N5O2)2

Abstract

A series of self-constituted quadruple hydrogen bonded (QHB) complexes (C₉H₉N₅O₂)₂ has been designed and studied systematically using density functional theory (B3LYP/6-31G**) and the Morokuma energy decompose method (HF/6-31G**). Despite very similar structures of these systems, the interaction energies fluctuate significantly from 22.33 to 88.30 kcal mol⁻¹. To explain this somewhat unexpected observation, several doubly hydrogen bonded (DHB) systems were designed and a “bending effect” hypothesis was presented. According to the hypothesis, the spatial arrangement of hydrogen bonds is less important than their intensity arrangement.