• A?nucleophile?is an electron-rich species that can?donate?a pair of electrons
  • ‘Nucleophile’ means ‘nucleus/positive charge loving’ as nucleophiles are attracted to positively charged species
  • Nucleophilic?refers to reactions that involve a nucleophile

   

• There are various different species which can behave as nucleophiles, and some make better nucleophiles than others

A hydroxide ion is a better nucleophile as it has a full formal negative charge whereas the oxygen atom in water only carries a partial negative charge

• A?nucleophilic substitution?reaction is one in which a?nucleophile?attacks a carbon atom which carries a?partial?positive?charge
• An atom that has a?partial?negative?charge?is replaced by the nucleophile
• Halogenoalkanes will undergo nucleophilic substitution reactions due to the polar C-X bond (where X is a halogen)

Due to large differences in electronegativity between the carbon and halogen atom, the C-X bond is polar

General Mechanism for Nucleophilic Substitution

• For example, in the following reaction a halogenoalkane reacts with aqueous alkali to form an alcohol

The halogen is replaced by a nucleophile, OH–

• The mechanism for the reaction is as follows

Nucleophilic substitution reaction of bromoethane and aqueous alkali (e.g. NaOH)