Substituent Effect Study for 13Cβ SCS in a Meta-Styrene Series. Reynolds Dual Substituent Parameter Model Investigation.

Abstract

This article investigates the transmission of the meta-substituent, X, effect to the carbon β (Cβ) of 17 different styrenes (X-C6H4-CH═CYZ) using the literature 13C substituent chemical shift (SCS) of Cβ. The 13C SCSs of Cβ were modeled by Reynolds substituent field σF and resonance σR constants. The model is considered a dual substituent parameter model, SCS = ρFσF + ρRσR. The coefficients of determination of the modeled 13C SCS for the 17 series fall between 0.9878 and 0.9983. The π-polarization concept was used to rationalize the field and resonance effects felt at Cβ. The ρF values of the meta-series were all lower than the para-series ρF values. The substituent field effect transmits to Cβ from Cipso. The substituent resonance effect transmits from Cipso to Cβ initially through the π-bond to Cortho and Cpara, next to the side chain, and then the generated charge will induce the vinyl group via π-polarization. The ρF felt at Cβ was almost double the ρR when compared with the short distance between Cmeta and Cβ, as opposed to Cortho and Cpara. Stabilization of the π-polarization of the vinyl group will increase, with the field and resonance effects felt at Cβ and vice versa.