Abstract: I3C NMR chemical shifts and deuterium isotope effects on chemical shifts in a, &unsaturated methoxycarbenium ions provide evidence regarding the influence of nonbonded interactions on charge distribution. The a,@-unsaturated methoxycarbenium ions exist as Z and E isomers due to restricted rotation about the C1-O bond. A 5-to 7-ppm difference between Z and E isomers at C,, which are sp2 carbons remote from the site of ...