Proton‐coupled carbon‐13 NMR spectra of butadienes

Proton‐coupled 13C NMR spectra were obtained for three methyl‐substituted butadienes, namely 2‐methylbuta‐1,3‐diene, trans‐2‐methylpenta‐1,3‐diene and 2,4‐dimethylpenta‐1,3‐diene. The second‐order spectra were analysed by computer, using some new 1H NMR data, and the resulting chemical shifts and coupling constants are reported. The parameters are related to conjugation (and, in turn, to conformation) of the compounds, and to the influence of σ and π pathways for coupling.