A theoretical investigation on the chemical environment of pyrazine-2,3-dicarbonitrile and phthalonitrile: Density functional theory (DFT) calculation and experimental verification

Abstract

Aromatic nitriles play an important role in the preparation of high-performance polymers. In order to guide the rational design of new molecules, it is necessary to carry out systematic theoretical research on molecular structures. This article takes a new type of aromatic nitriles, pyrazine-2,3-dicarbonitrile (PQ) and its control group 1,4-dicyanobenzene (PN) as examples to conduct systematic theoretical research on their chemical environments using DFT calculation with experimental verification. Results show that the electronic effect of pyrazine withdraws the electron form cyano to pyrazine, which makes the cyano carbon more exposed and prone to nucleophilic reaction. This electronic deffect also causes the π-electron delocalization from cyano nitrogen to pyrazine, and results in a lower polarity of the cyano and an anomalous law for the 13C NMR shift of cyano carbon. In addition, pyrazine changes the stacking mechanism of PQ to be dominated by electrostatic force rather than commonly observed dispersion force-dominant π-π stacking in PN. This research method provides important guidance for the design of new crosslinkable aromatic nitrile and help to deepen our understanding of their structure-property relationship.