Which of the following is strongest base ?

Question

Accepted Answer

Dimethylamine is the strongest base among the given options. Here's a detailed explanation supporting this:

1. **Dimethylamine (Option 1):** Dimethylamine is a secondary amine with two methyl groups attached to the nitrogen atom. The presence of these alkyl groups increases the electron density on the nitrogen through the +I (inductive) effect, making the lone pair of electrons on nitrogen more available for donation. This increased electron density enhances the basicity of dimethylamine, making it a stronger base compared to the other options.

2. **Triethylamine (Option 2):** Although triethylamine is a tertiary amine with three ethyl groups, which also provide an inductive effect, the steric hindrance caused by the bulky ethyl groups reduces the accessibility of the lone pair on nitrogen. This steric hindrance makes it less effective in accepting protons compared to dimethylamine, thus reducing its basicity.

3. **Ammonia (Option 3):** Ammonia is a simple molecule with no alkyl groups attached to the nitrogen. It lacks the electron-donating inductive effect that alkyl groups provide, making its lone pair less available for donation compared to dimethylamine. Therefore, ammonia is a weaker base than dimethylamine.

4. **Aniline (Option 4):** Aniline is an aromatic amine where the nitrogen is directly attached to a benzene ring. The lone pair of electrons on the nitrogen is delocalized into the aromatic ring, reducing its availability for protonation. This delocalization significantly decreases the basicity of aniline compared to aliphatic amines like dimethylamine.

In conclusion, dimethylamine is the strongest base among the given options due to the electron-donating inductive effect of its methyl groups, which increases the electron density on the nitrogen and enhances its ability to accept protons.