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Abstract
The benzothiazole ring is used to express the C-H hyperconjugation effect in the fundamental state. 13C NMR spectra at infinite dilution in CDCl3 have been recorded for a set of 2-substituted benzothiazoles with groups having a different number (0 to 3) of hydrogen atoms bound to the Cα carbon. The carbon-2 chemical shift variation reflects the superposition of a rather weak inductive effect and a high Cα-H hyperconjugation effect. In the particular case of α-β unsaturated groups, π - π resonance shows a similar influence. A semi-empirical relationship allowing precise quantitative evaluation of carbon-2 chemical shift has been established.