Illustrated Glossary of Organic Chemistry

Nucleophilicity: The extent to which a molecule is nucleophilic. A qualitative (not quantitative) term, although often illustrated with relative reaction rates (k_rel).

Nuc:   +

SN2 CH3OH

+   I-

Nucleophile	F-		Cl-		Br-		I-
krel	1.5 x 10-5		8.8 x 10-4		2.4 x 10-2		1.0

This reaction rate data reveals that in CH₃OH, iodide ion (I^-) is more nucleophilic (i.e., it has higher nucleophilicity and reacts faster with CH₃I) than other halide ions.