14N NQR study of selected 1,4-benzoquinonedioximes |
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Authors: | N Singh D Stephenson |
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Institution: | 1. Chemistry Department, University of the West Indies, St. Augustine, Trinidad and Tobago
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Abstract: | The 14N NQR frequencies of selected 1,4-benzoquinonedioximes were measured using cross relaxation double resonance. As the number of substituents increase, a significant shift in the NQR values is observed. Comparison of unsubstituted and tri-substituted 1,4-benzoquinonedioximes shows that the quadrupole coupling constant (χ) increases by about 1000 kHz and the asymmetry parameter (η) decreases from ≈0.7 to 0.3 respectively. Ab-initio calculations show that for the unsubstituted compound hydrogen bonding between oxime groups and pi-ring stacking is possible which cannot be accommodated for in heavily methyl substituted dioximes and this results in distinct NQR parameters. |
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