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 (krel).

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.