Basic Properties of Amines

Why do amines act as bases?

• Because the nitrogen atom has a lone pair of electrons that can accept a proton (H⁺).

Why are aliphatic amines (e.g., methylamine) stronger bases than ammonia?

• Alkyl groups are electron-releasing. They increase the electron density on the nitrogen's lone pair, making it more available to accept a proton.

Why are aromatic amines (e.g., phenylamine) weaker bases than ammonia?

• The lone pair on the nitrogen delocalises into the benzene ring's π-system. This makes the lone pair less available to accept a proton.

Write the equation for ethylamine acting as a base in water.

• CH₃CH₂NH₂ + H₂O ⇌ CH₃CH₂NH₃⁺ + OH⁻

What is the general product when an amine reacts with an acid?

• An alkylammonium salt.
  Example: CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻

What is the name of the salt formed when propylamine reacts with nitric acid?

• Propylammonium nitrate (CH₃CH₂CH₂NH₃⁺NO₃⁻)

Explain the base strength difference between ethylamine and phenylamine.

1. Ethylamine is a stronger base than phenylamine.

2. In ethylamine, the alkyl group is electron-releasing, which increases the electron density on the nitrogen's lone pair, making it more available to accept a proton.

3. In phenylamine, the lone pair on the nitrogen delocalises into the stable benzene π-ring.

4. This delocalisation makes the lone pair less available to accept a proton, resulting in a weaker base.

Equation for methylamine + HCl and name the product.

• CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻

• Name of Product: Methylammonium chloride

Explain how the positive inductive effect increases base strength.

• The alkyl group pushes electron density towards the nitrogen atom.

• This increases the electron density on the nitrogen's lone pair.

• A lone pair with higher electron density is more readily available to form a bond with a proton (H⁺), making the amine a stronger base.