Illustrated Glossary of Organic Chemistry

Nucleophilic aromatic substitution (NAS): A substitution reaction in which attack on an aromatic ring by a nucleophile replaces a substituent (or in the case of the Chichibabin reaction a hydride ion) on that aromatic ring.

Reaction of o-fluoronitrobenzene with methoxide ion (a nucleophile) follows the SNAr nucleophilic aromatic substitution reaction mechanism.