Studies on the linear free energy relationship in methyl cinnamates by 1H-NMR spectrometry

Chemical shift values of α-proton of trans- and cis-methyl cinnamates are well correlated with σ(σsub(I),σ0sub(R)), and (F,R) (r=0.999-0.879). It is observed that (1) the degree of variation of σHα value by varying the substituents in transcinnamates is similar to that of cis- cinnamates (lsub(trans)=0.296, lsub(cis)=0.284), (2) resonance contribution is larger in the trans-cinnamates than that in the cis-cinnamates, but inductive contribution is reversed, (3) for m-substitude derivatives, resonance contribution is very small compared to that for p-substituted derivatives. (author)