The Cyanide ion (:CN^–) acts as a nucleophile because it has a lone pair of electrons on the carbon atom.

Bromoethane has a polar C-Br bond, creating a partially positive (δ+) carbon atom which is vulnerable to attack by the lone pair.

Conditions: Heat under reflux; dissolved in an ethanol and water mixture.

Explanation: Halogenoalkanes are soluble in ethanol (organic solvent) but insoluble in water. Potassium Cyanide is soluble in water (ionic) but insoluble in ethanol. A mixture of both solvents allows the reactants to mix and react.

Nucleophilic Substitution

Name: 2-methylbutanenitrile

(Note: The carbon in the nitrile group becomes Carbon-1 of the chain).

Correct Answer: The product (2-methylbutanenitrile) has a chiral centre at carbon-2, which is bonded to four different groups (-H, -CH₃, -CH₂CH₃, -CN). Therefore, it exists as enantiomers and will rotate plane polarised light (unless it forms as a racemic mixture).

(Note: Some sources may incorrectly state it has no effect if they confuse the reactant with 2-chloropropane, which would form an achiral product. For 2-chlorobutane, the product is chiral).

Potassium Cyanide (KCN) or Sodium Cyanide (NaCN).

Hydrogen cyanide (HCN) is a weak acid, so it partially dissociates and produces a very low concentration of nucleophilic cyanide ions (CN^–). Additionally, HCN is a highly toxic gas which makes it dangerous to handle.

1. The lone pair on the carbon atom of the cyanide ion attacks the partially positive carbon atom of the chloromethane, forming a new C-C bond.

2. The C-Cl bond breaks heterolytically, with both electrons from the bond moving onto the chlorine atom, forming a chloride ion (Cl^–).