Final answer:
A nucleophilic substitution reaction occurs when a nucleophile replaces another nucleophile on a substrate. The stereochemistry of the reaction is inverted through an unstable transition state. An example of a nucleophilic substitution reaction is the O-methylation of an alcohol using methyl iodide as the substrate.
Step-by-step explanation:
A nucleophilic substitution reaction occurs when a nucleophile (Nu) replaces another nucleophile (X) on a substrate. In this type of reaction, the nucleophile attacks the carbon atom while the leaving group (X) leaves. The stereochemistry of the reaction is inverted through an unstable transition state. An example of a nucleophilic substitution reaction is the O-methylation of an alcohol using methyl iodide as the substrate.