Chemistry · General Principles Of Organic Chemistry · NEET
A base is anything that can donate its lone pair of electrons. So an organic compound is MORE basic when the lone pair on its nitrogen (or oxygen) is easy to give away. Alkyl groups push electrons toward nitrogen (+I effect), making amines stronger bases; but in aniline the nitrogen lone pair leaks into the benzene ring by resonance, so it is held back and aniline is a weak base. Memory hook: "Lone pair FREE = strong base; lone pair TRAPPED in the ring = weak base."
Left: in an alkyl amine the +I effect pushes electrons onto nitrogen and the lone pair stays free, so it donates easily (strong base). Right: in aniline the nitrogen lone pair delocalises into the benzene ring by resonance, so it is trapped and hard to donate (weak base). On the ring, electron donors like -CH3 raise basicity while -NO2 lowers it.
Your doubts, answered
What actually makes an organic compound basic?
A base donates a lone pair of electrons (Lewis) or accepts a proton H+ (Bronsted). In amines the nitrogen has a lone pair. If that lone pair is easy to donate, the compound is a strong base. Anything that makes the lone pair MORE available (like +I electron-donating alkyl groups) raises basicity. Anything that pulls the lone pair away (resonance into a ring, or -I/-M electron-withdrawing groups) lowers basicity.
Why is aniline less basic than methylamine?
In aniline (C6H5-NH2) the nitrogen lone pair is in conjugation with the benzene ring. It spreads out (delocalises) into the ring by resonance (+M into the ring), so it is not fully sitting on nitrogen and is less available to grab a proton. In methylamine the lone pair stays on nitrogen and the +I of the methyl group even pushes more electron density onto it. So methylamine (and all alkyl amines) are stronger bases than aniline.
What is the correct order of basicity of aromatic amines like aniline, p-toluidine and p-nitroaniline?
Look at the group on the ring. -CH3 (in p-toluidine) donates electrons (+I / hyperconjugation), so it makes the N lone pair MORE available: strongest base. -NO2 (in p-nitroaniline) strongly withdraws electrons (-I and -M), pulling the lone pair away: weakest base. So order is p-nitroaniline < aniline < p-toluidine. This is the exact NEET 2017 answer (II < I < III).
Why is (CH3)2NH more basic than (CH3)3N in water? Shouldn't more methyl groups mean more basic?
By +I effect alone, trimethylamine should be strongest. But in WATER two more things matter: (1) steric crowding - three bulky methyls block the proton from reaching nitrogen, and (2) solvation - the protonated cation is stabilised by hydrogen bonding to water, and having more N-H bonds gives more H-bonding. Trimethylamine has no N-H left, so it is poorly solvated. The net result in water is (CH3)2NH > CH3NH2 > (CH3)3N. This is the NEET 2019 answer.
Do electron-withdrawing groups increase or decrease basicity?
They DECREASE basicity. Electron-withdrawing groups (like -NO2, -C=O, or the benzene ring by resonance) pull electron density AWAY from nitrogen or oxygen, so the lone pair is less available to donate. This is why phenol is the hardest to protonate (NEET 2019) and p-nitroaniline is the weakest base. It is the exact opposite of acidity, where electron-withdrawing groups make things MORE acidic.
Is aniline a base or an acid?
Aniline is a base (a weak one), not an acid. Its nitrogen still has a lone pair that can accept a proton, so it is basic. But because that lone pair is partly pulled into the ring by resonance, aniline is a much weaker base than aliphatic amines like methylamine or diethylamine.
⚠️ The NEET trap ✗ Thinking more alkyl groups always means more basic, so (CH3)3N > (CH3)2NH > CH3NH2, or thinking aniline is more basic because 'the ring adds electrons.' ✓ In WATER the order of methylamines is (CH3)2NH > CH3NH2 > (CH3)3N (solvation + steric effects flip pure +I). And aniline is LESS basic than alkyl amines because the ring PULLS the lone pair away by resonance. 🧠 In water, basicity is a tug-of-war between +I (pushing electrons in) and steric/solvation (blocking the proton). The winner is usually the secondary amine, not the tertiary one.
Real NEET questions
NEET 2016 Phase 1
The correct statement regarding the basicity of aryl amines is:
A · Aryl amines are generally less basic than alkyl amines because the nitrogen lone-pair electrons are delocalised by interaction with the aromatic ring pi electron system. ✓
B · Aryl amines are generally more basic than alkyl amines because the nitrogen lone-pair electrons are not delocalised by interaction with the aromatic ring pi electron system.
C · Aryl amines are generally more basic than alkyl amines because of the aryl group.
D · Aryl amines are generally more basic than alkyl amines because the nitrogen atom in aryl amines is sp-hybridised.
Solution: In aniline the N lone pair conjugates with the ring and delocalises into it (+M), so it is less available to grab a proton. In alkyl amines the lone pair stays on N and is boosted by +I of alkyl groups. So aryl amines are LESS basic than alkyl amines because of lone-pair delocalisation. Answer (A).
NEET 2017
The correct increasing order of basic strength for: (I) aniline, (II) p-nitroaniline, (III) p-toluidine (4-methylaniline).
A · II < III < I
B · III < I < II
C · III < II < I
D · II < I < III ✓
Solution: -NO2 (strong -M/-I) pulls the N lone pair away, so p-nitroaniline (II) is weakest. -CH3 (+I) pushes electrons in, so p-toluidine (III) is strongest. Order: II < I < III. Answer (D).
NEET 2019
The correct order of the basic strength of methyl-substituted amines in aqueous solution is:
A · (CH3)2NH > CH3NH2 > (CH3)3N ✓
B · (CH3)3N > CH3NH2 > (CH3)2NH
C · (CH3)3N > (CH3)2NH > CH3NH2
D · CH3NH2 > (CH3)2NH > (CH3)3N
Solution: In water three things compete: +I effect (more methyls = more electron push), steric hindrance (bulky groups block the proton), and solvation (more N-H bonds = better H-bonding of the cation). The net winner is the secondary amine: (CH3)2NH > CH3NH2 > (CH3)3N. Trimethylamine is least basic due to crowding and poor solvation. Answer (A).
Solved General Principles Of Organic Chemistry NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Ammonia is more basic than aniline. In aniline the nitrogen lone pair is partly delocalised into the benzene ring, so it is less available to accept a proton. Ammonia's lone pair is fully free on nitrogen.
What is the basicity order aniline vs methylamine vs ammonia?
Basicity: methylamine (CH3NH2) > ammonia (NH3) > aniline (C6H5NH2). The +I methyl group raises basicity above ammonia, while ring resonance in aniline lowers it below ammonia.
Why does p-nitroaniline have very low basicity?
The -NO2 group is strongly electron-withdrawing (-I and -M). It pulls electron density and the lone pair away from nitrogen, so the lone pair is barely available to accept a proton, making p-nitroaniline a very weak base.
How is basicity measured, by Kb or pKb?
Basicity is measured by Kb (base dissociation constant) or pKb = -log Kb. A larger Kb (or a smaller pKb) means a stronger base.
Is basicity the opposite of acidity for these effects?
Yes, in effect. Electron-donating groups (+I) increase basicity but decrease acidity. Electron-withdrawing groups (-I/-M) decrease basicity but increase acidity.
