13C NMR: nJCH and 1JCC scalar spin–spin coupling constants (SSCCs) for some 3-monosubstituted 2-methylpropenes

Twelve methallylic derivatives were studied using 13C NMR spectroscopy and theoretical calculations. Theoretical coupling constants were obtained with SOPPA (CCSD). All atoms were described by the EPR-III basis set, except for halogens, which were represented by the cc-pVTZ basis set. Geometries were optimized at the MP2/aug-cc-pVTZ level of theory, confirming previous results that the gauche and s-cis conformers predominate. Experimental nJCH coupling constants were determined from coupled 13C NMR spectra, while the 1JCC couplings were measured through the INADEQUATE technique. The experimental and theoretical values were in good agreement. Correlations with the usual substituent physicochemical parameters indicated that the 1 J C 3 H c values (where Hc is attached to the C3 carbon bearing the substituent) exhibit good correlations with Taft’s sigma (σI inductive parameter) and the Swain–Lupton Field Effect (F) (R ∼ 0.957), while other correlations were not similarly significant (R values <0.9).