Understanding Basicity in Gaseous Phase
When discussing the basicity of amines in the gaseous phase, we are often interested in how readily they can accept protons (H+). The strength of a base is largely influenced by its structure and the availability of the lone pair of electrons on the nitrogen atom.
Factors Influencing Basicity
- Electron-donating Groups: Alkyl groups are electron-donating, which increases the electron density on the nitrogen atom, enhancing basicity.
- Steric Hindrance: Larger alkyl groups can create steric hindrance, making it harder for the nitrogen to interact with protons.
- Hybridization: The hybridization state of the nitrogen atom can also impact its ability to donate its lone pair.
Comparison of the Given Amines
- Triethyl Amine: Has three ethyl groups which provide significant electron-donating effects, making it a strong base.
- Diethyl Amine: With two ethyl groups, it is still a strong base but less so than triethyl amine due to increased steric hindrance.
- Ethyl Amine: Contains one ethyl group, making it a weaker base compared to diethyl and triethyl amines, yet stronger than ammonia.
- Ammonia: Lacks any alkyl groups, which diminishes its ability to stabilize the positive charge that forms when it accepts a proton.
Conclusion
Among the options provided, ammonia is the weakest base in the gaseous phase due to its lack of electron-donating alkyl groups and minimal steric hindrance. Its lone pair is less available for protonation compared to the other amines, making it a less effective base overall. Therefore, the correct answer is option 'D' (Ammonia).