The electron density on a carbon atom determines the C-13 chemical shift; observed in the NMR spectrum. In a vinyl monomer, the same electron density must contribute strongly to polar effects involved in the addition of a radical to that monomer and possibly in the addition (to a double bond) of a radical terminated by a unit derived from that monomer. It is shown that the expected correlation exists when the polar effects in polymerization reactions are represented by the parameters of the revised patterns scheme.