Question

The amine which is most basic in gas phase is:

• A. \(\mathrm{CH}_3\mathrm{NH}_2\)
• B. \(\mathrm{NH}_3\)
• C. \(\left(\mathrm{CH}_3\right)_2\mathrm{NH}\)
• D. \(\left(\mathrm{CH}_3\right)_3\mathrm{N}\)

Hint:

For amine basicity:

- In gas phase: Tertiary>secondary>primary>ammonia due to inductive effects.

- In aqueous solution, solvation reverses the order (secondary>tertiary).

- Consider electron donation and stabilization of the protonated form.

Answer 1

The Correct Option is D

The basicity of amines in the gas phase depends on their ability to donate a lone pair of electrons to a proton, forming \({R3NH^+}\). Unlike in aqueous solution, gas-phase basicity is not influenced by solvation effects.
Step 1: Understand gas-phase basicity
Alkyl groups (\({CH3}\)) are electron-donating due to their inductive effect, increasing electron density on the nitrogen atom. More alkyl groups enhance the amine’s ability to stabilize the protonated form (\({R3NH^+}\)), increasing basicity. The order of basicity in the gas phase is: \[ \text{tertiary amine}>\text{secondary amine}>\text{primary amine}>\text{ammonia} \]
Step 2: Analyze options
- (A) \(\mathrm{CH}_3\mathrm{NH}_2\): Primary amine, one alkyl group, less electron donation.
- (B) \(\mathrm{NH}_3\): No alkyl groups, least basic.
- (C) \(\left(\mathrm{CH}_3\right)_2\mathrm{NH}\): Secondary amine, two alkyl groups, more basic than primary.
- (D) \(\left(\mathrm{CH}_3\right)_3\mathrm{N}\): Tertiary amine, three alkyl groups, most basic due to maximum electron donation.
Step 3: Conclusion
In the gas phase, \(\left(\mathrm{CH}_3\right)_3\mathrm{N}\) (tertiary amine) is the most basic, matching option (D).