9-Alkenylcarbazoles. 10. ¹³C NMR spectra of 9-vinyl- and cis- and trans-9-propenylcarbazoles

The ¹³C NMR spectra of a number of ring-substituted 9-vinylcarbazoles and cis- and trans-9-propenylcarbazoles were studied. It was found that the C_B chemical shifts of the vinyl atoms of these compounds correlate satisfactorily with the σ constants of the substituents in the 3 and 6 position of the carbazolyl rings; the slopes of the straight lines increase in the order 5.84, 7.68, 9.56. The inductive and conjugation components of the effect of the substituents on the chemical shifts of the C_B atoms were evaluated. It follows from the results obtained that the effects of p-π conjugation are realized not only in the relatively planar isomers but also in the nonplanar cis isomers of 9-alkenylcarbazoles.