Carbon‐13 NMR spectra of monosubstituted pyrazines

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Abstract
Carbon‐13 NMR chemical shifts and one‐bond carbon–hydrogen coupling constants have been obtained at 15·09 MHz. The trends in the carbon chemical shifts obtained for the pyrazines parallel those of monosubstituted benzenes and 2‐substituted pyridines, except for the direct effect of substitution where the pyrazines resemble pyridines not benzenes. The substituent effects on the 13C NMR spectra are generally quite similar to those in the 1H NMR spectra. The 13C NMR spectrum of the tautomeric hydroxypyrazine has been compared with the 13C NMR spectra of 2‐, 3‐ and 4‐hydroxypyridines. Hydroxy compounds that can exist as a cyclic amide show a large meta substituent effect on the chemical carbon shift.