β-Substituent effects in the 13C NMR chemical shifts of styrenes
Abstract
The effects of meta and para ring substituents on the 13C NMR chemical shifts of the β-carbon of a series of β-heteroaryl styrenes has been investigated. The results show that the contribution of the resonance effect of para substituents to the C-β chemical shift depends on both the polar and resonance effect of the β-substituent, and not, as was previously believed, on the resonance effect alone.