The Nuclear Magnetic Resonance Spectra of Olefinic Protons and the Substituent Effects. I. Systems of ω-Substituted trans-Styrenes and 1-Substituted trans-Propenes

High resolution proton magnetic resonance spectra of ω-substituted trans-styrenes and 1-substituted trans-properies have been observed and discussed from the viewpoint of substituent effects. The chemical shifts of protons located at the cis-position to substituents depend roughly upon Hammett’s σP constants and presumably correlate better with the combination of potential inductive and resonance parameters, namely 0.40σI+0.70σR, proposed by Taft. These results suggest that the chemical shifts of olefinic cis-proton may be computed from the viewpoint of the polar nature of the substituents, though the diamagnetic anisotropy and the long-range shielding effect of the substituents must be carefully considered side by side. When the chemical shifts of protons situated at corresponding positions of structure in several systems are compared, a fairly good correlation is observed among them. This fact implies that the modes of the transmittance of substituent effects is similar in these systems. The nature of the substituent effects on the chemical shifts of geminal protons is, however, very complicated and might be out of consonance with both the electronegativity and the available substituent parameters.