14N nuclear quadrupole coupling in solid cinnolin-4-ones. A study by nuclear quadrupole resonance, x-ray crystallography and ab initio calculations

Abstract

The 14N nuclear quadrupole coupling constants (NQCCs) for 1H-cinnolin-4-one and its 1- and 2-methyl derivatives have been obtained by nuclear quadrupole double resonance. The X-ray crystal structures of the 1H and 1Me compounds have been solved, and show lengths and angles consistent with related heterocycles; attempts to obtain an X-ray structure for the 2Me compound have so far been unsuccessful owing to disorder. Computed equilibrium structures by ab initio SCF methods for the Me derivatives and also the experimental 1H structures yielded electric field gradients, which were converted into NQCCs in reasonable agreement with experiment. The 2Me compound has unusual NQCC, both experimentally and in the theoretical study.