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

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2021-09, Vol.125 (36), p.7759-7768
• Main Authors: Saleh, Basil A, Al-Shawi, Sabih A, Fadhil, Ghazwan F
• Format: Article
• Language: English
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.1c02645

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.