Proton magnetic resonance spectra of some β-methylstyrenes, β,β-dimethylstyrenes, and α-methylstilbenes; and a discussion of long-range shieldingand coupling effects in these and related systems

The preparation of some new β,β-dimethylstyrenes and α-methylstilbenes is described and their p.m.r. spectra are reported. The long-range shielding effects in β,β-dimethylstyrenes and other styrene derivatives are discussed. The differences between the cisoid and transoid allylic coupling constants in β,β-dimethylstyrenes are much smaller than the corresponding differences in simple propenes. No appreciable (J ≥ 0.3 c/s) coupling between the non-equivalent methyl protons in β,β-dimethylstyrenes has been observed. Long-range coupling in the compounds investigated appears to be independent of ring substitution. Some general features of allylic coupling are discussed.