Transmission of substituent effects through the unsaturated system in ring-substituted α-methoxystyrenes and related compounds

A ¹³C NMR study of the transmission of substituent effects in m- and p-substituted derivatives of α-MeO-styrene and the E and Z forms of α-MeO-β-Me-styrene has been performed. The CC bond of vinyl ethers is a considerably weaker transmitter of substituent effects than that of ordinary alkenes, especially if p-π conjugation in the vinyloxy system is unhindered. In each series of compounds studied, a fairly good linear correlation exists between the ¹³C chemical shift of the β carbon and the Hammett σ parameter. The worst linear correlation was obtained for the C-β shifts of α-MeO-styrenes. The shifts concerned, however, were nicely correlated with the Hammett σ⁺ parameter.