Chemical shifts of ethylenic protons in CIS and TRANS β‐Arylthio‐, β‐arylsulfinyl‐and β‐arylsulfonyl‐acrylic acids

Chemical shifts of the ethylenic protons Hα and Hβ in cis and trans β-arylthio-,β-arylsulfinyl- and β-arylsulfonyl-acrylic acids have been determined in acetone and in Na2CO3/D2O solution. The absorption signals were assigned unambiguously by β-deuteration. An increase of electron-withdrawing power of the β-substituent (ArSO2 > ArSO > ArS) causes an increase in shielding of Hβ proton and a decrease in that of Hα proton. The τ-values of the Hβ protons are lower in the trans than in the corresponding cis acids, which may be explained in terms of magnetic anisotropy effects of the carboxyl group in the trans acids. Generally, the τ-values of the Hβ protons are lower, and those of the Hα protons higher, in acetone than in Na2CO3/D2O solution; this is probably due to differences in electron-withdrawing power of the COOH and COO⊙ groups. In all trans derivatives the average values of the coupling constants Jαβ are 15.3 c./sec., and lie between 10.1-11.4 c./sec. for the cis derivatives. The effects of para-substituents (CH3O, CH3, H, Cl, NO2) on the chemical shifts of the Hα and Hβ protons in cis and trans β-arylthio-, β-arylsulfinyl-, and β-arylsulfonyl-acrylic acids are correlated with the Hammett σ-constants.