The Determination of Substituent Effects by 13C Nuclear Magnetic Resonance Spectrometry. The Effect of Solvent on CH₂X Groups

Abstract

A previous study of the effect of meta- and para-CH₂X substituents on the ¹³C n.m.r. chemical shifts of the α and β side-chain carbons of β- methoxycarbonylstyrenes (methyl cinnamates ) in ethanol has been extended to cover five additional solvents (Me₂SO, Me₂CO, CDCl₃, CCl₄ and C₆H₆). The results support the earlier claim that, for most substituents , the magnitudes of the substituent -induced shifts are proportional to the inductive effect of X. The major contributor to the latter appears to be the field effect generated by the C-X dipole, with the lines of force passing mainly through the molecule. In non-polar solvents, however, there is evidence that lines of force passing directly through the solvent can also influence the shifts in both the meta and para series.