13C nuclear magnetic resonance spectra of quinoxaline derivatives
- 1 January 1982
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 1
- p. 357-363
- https://doi.org/10.1039/p19820000357
Abstract
The 13C n.m.r. spectra of a series of 5-, 6-, and 2-substituted quinoxalines have been analysed by consideration of their 1H-coupled spectra. Typical values of the coupling constants are: C(2,3),1JCH 181.9,2JCH 11.4; C(5,8), 1JCH 162.6, 3JCH 6.5, C(6,7), 1JCH 159.4, 3JCH 9.1; C(9), 3JCH(2)=3JCH(7)= 10.0, 3JCH(5) 5.4; C(10), 3JCH(3)=3JCH(6)= 10.0, 3JCH(8) 5.4 Hz. The magnitudes of the coupling constants in the benzenoid ring [C(5)–C(10)] are similar to these for the corresponding positions in naphthalene, but application of naphthalene chemical shift substitutions effects leads in some cases to the wrong peak sequence in the related quinoxalines. Within the quinoxaline series itself, however, acceptable additivity of substituent effects is found (±0.8 p.p.m.), provided that the reference compounds are carefully chosen. Analysis of mixtures of quinoxalines from substituted o-phenylenediamines and α-oxo-aldehydes is possible by consideration of the multiplicity of the ring-junction quaternary carbon signals in the fully coupled spectra.Keywords
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