Chemistry · Amines · NEET
In the gas phase the amine molecule stands alone with no solvent around it. The only factor left is the +I (electron-pushing) effect of the alkyl groups. Each alkyl group added to nitrogen pushes more electron density onto the lone pair, making it more available to grab a proton. So a tertiary amine (3 alkyl groups) is the strongest base, then secondary (2), then primary (1), and ammonia (0 alkyl groups) is the weakest.
In water the ion formed after gaining a proton must be stabilised by water molecules (solvation). A primary ammonium ion (R-NH3+) has 3 N-H bonds and is best surrounded and stabilised by water, while a tertiary ammonium ion (R3NH+) has only 1 N-H bond and is poorly solvated. Water 'rewards' the ions that it can hold better, so the clean gas-phase order (3°>2°>1°) gets scrambled. That is a separate topic: role of solvation in amine basicity.
No. Solvation and hydration only happen when a solvent like water is present. In the gas phase there is no solvent, so no solvation and no hydrogen bonding to a solvent. That is exactly why the gas-phase result is 'pure' — it shows what the inductive effect alone would do.
For NEET, the gas-phase inductive-only picture treats +I as the deciding factor and gives 3°>2°>1°>NH3. Steric crowding around a large tertiary amine can slightly lower how easily the proton reaches nitrogen, but that is a separate refinement. The clean answer expected here is the pure inductive order: more alkyl groups means stronger base.
Methylamine. Ammonia has zero alkyl groups, while methylamine has one CH3 group pushing electron density onto nitrogen by +I. More electron density on the lone pair means a stronger base, so methylamine > ammonia in the gas phase.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
3° amine > 2° amine > 1° amine > NH3. Only the +I inductive effect operates because there is no solvent.
It has the most alkyl groups, so the most +I electron push onto nitrogen, giving the most available lone pair and the strongest base.
Ammonia has no alkyl groups, so no +I electron donation onto the nitrogen lone pair, making its lone pair least electron-rich.
NEET usually asks the water (aqueous) order, which includes solvation and can reverse the trend. Knowing the clean gas-phase order helps you spot when solvation has changed the answer.
Only the inductive (+I) effect of alkyl groups. No solvation, no hydrogen bonding to solvent, no steric override in the clean picture.
