Six standard methods give a primary (1°) amine: reduction of nitro compounds, reduction of nitriles, reduction of amides, Gabriel phthalimide synthesis, Hoffmann bromamide degradation, and ammonolysis of alkyl halides. The one trap that does NOT give a 1° amine is reduction of an isocyanide (R-NC), which gives a 2° amine. Memory hook: "NNAGH gives 1°, but NC breaks the rule" (Nitro, Nitrile, Amide, Gabriel, Hoffmann = 1°; iso-Cyanide = 2°).
Six standard preparations give a primary amine (nitrogen on one carbon). Reduction of an isocyanide is the NEET trap: it puts nitrogen on two carbons, giving a secondary amine.
Your doubts, answered
Which methods actually give a PURE primary amine?
Five methods give a clean 1° amine as the main product: (1) reduction of a nitro compound (Sn/HCl or H2/Ni), (2) reduction of a nitrile with LiAlH4 or H2/Ni, (3) reduction of an amide with LiAlH4, (4) Gabriel phthalimide synthesis, and (5) Hoffmann bromamide degradation. In all five, the nitrogen ends up attached to only ONE carbon, which is the definition of a 1° amine.
Why does reduction of an isocyanide (R-NC) give a SECONDARY amine, not primary?
In an isocyanide R-N≡C, the nitrogen is already bonded to the R carbon AND to the isocyanide carbon. When you reduce it (LiAlH4), that isocyanide carbon becomes a CH3-type group still attached to N. So N ends up bonded to TWO carbons: R-NH-CH3. Two carbons on N means a 2° amine. This is the most common NEET trap (asked in NEET 2023).
Does ammonolysis of alkyl halides give a primary amine?
Yes, it CAN give a 1° amine, but not cleanly. R-X + NH3 gives R-NH2, but the 1° amine formed is still nucleophilic and attacks more R-X, giving 2° amine, then 3° amine, and finally a quaternary salt. So you get a MIXTURE. Using a large excess of ammonia favours the 1° amine. For a pure 1° amine, Gabriel synthesis is better.
Why does Gabriel synthesis give ONLY a primary amine (never 2° or 3°)?
In Gabriel synthesis, the nitrogen is 'locked' inside the phthalimide ring, so only ONE alkyl group can attach to it. After hydrolysis you release R-NH2, a pure 1° amine, with no mixture. Note: it FAILS for aryl amines like aniline because aryl halides do not undergo the needed substitution.
How does Hoffmann bromamide give a primary amine, and why one less carbon?
Hoffmann bromamide degradation takes an amide R-CONH2 and treats it with Br2 + KOH (or NaOH). The C=O carbon leaves as carbonate, and N stays attached to R only. So you get R-NH2, a 1° amine with ONE FEWER carbon than the starting amide. Example: CH3CONH2 (2 carbons) gives CH3NH2 (1 carbon).
Nitrile reduction vs Hoffmann bromamide — do they change the carbon count?
They differ. Nitrile reduction R-CN gives R-CH2-NH2, which ADDS one carbon to the chain and gives a 1° amine. Hoffmann bromamide of an amide R-CONH2 gives R-NH2, which LOSES one carbon. So both give 1° amines, but nitrile reduction adds a carbon while Hoffmann bromamide removes one. NEET loves testing this carbon-count difference.
Does NaBH4 reduce a nitro group to an amine?
No. NaBH4 is a mild reducing agent and does NOT reduce the aromatic nitro group. To reduce nitrobenzene to aniline you must use Sn/HCl, Fe/HCl, or H2/Ni (catalytic hydrogenation). This point was tested in NEET (ReNEET 2026): C6H5NO2 with NaBH4 = no reaction, not aniline.
⚠️ The NEET trap ✗ Reduction of methyl isocyanide (CH3-NC) with LiAlH4 gives a primary amine because it has a -NC group with nitrogen. ✓ Reduction of an isocyanide gives a SECONDARY amine. In CH3-NC the nitrogen is bonded to CH3 and to the isocyanide carbon; on reduction that carbon becomes CH3, so N is bonded to two carbons: CH3-NH-CH3. Two carbons on N = 2° amine. 🧠 Nitr-I-le (R-CN) gives 1°; iso-cyan-I-de (R-NC) gives 2°. The extra carbon between R and N stays attached — that is what makes it secondary.
Real NEET questions
NEET 2023
Which of the following reactions will NOT give a primary amine as the product?
A · CH3CONH2 →[Br2/KOH] Product
B · CH3CN →[(i) LiAlH4 (ii) H3O+] Product
C · CH3NC →[(i) LiAlH4 (ii) H3O+] Product ✓
D · CH3CONH2 →[(i) LiAlH4 (ii) H3O+] Product
Solution: Reduction of the isocyanide CH3NC gives CH3-NH-CH3, an N-methyl SECONDARY amine (N bonded to two carbons), so it does NOT give a 1° amine. The others all give 1° amines: (A) Hoffmann bromamide CH3CONH2 → CH3NH2; (B) nitrile reduction CH3CN → CH3CH2NH2; (D) amide reduction CH3CONH2 → CH3CH2NH2. Hence the answer is (C).
NEET 2017
Which of the following reactions is appropriate for converting acetamide (CH3CONH2) to methanamine (CH3NH2)?
A · Carbylamine reaction
B · Hoffmann bromamide (hypobromamide) reaction ✓
C · Stephen's reaction
D · Gabriel's phthalimide synthesis
Solution: Acetamide has 2 carbons; methanamine has 1 carbon — so we need a method that gives a 1° amine with ONE FEWER carbon. Hoffmann bromamide degradation (Br2/KOH) does exactly this: CH3CONH2 → CH3NH2. Carbylamine (A) is only a TEST for 1° amines, not a preparation. Stephen's reaction (C) reduces nitriles to aldehydes. Gabriel synthesis (D) uses alkyl halides, not amides. Answer: (B).
ReNEET 2026
Identify the reactions which give aniline as the major product. (A) C6H5CN →[LiAlH4]; (B) C6H5CONH2 →[KOH, Br2]; (C) C6H5NO2 →[NaBH4]; (D) C6H5NHCOCH3 →[HCl, H2O, Δ].
A · A and B only
B · B and D only ✓
C · A and C only
D · C and D only
Solution: (A) LiAlH4 reduces benzonitrile to BENZYLAMINE C6H5CH2NH2 (an extra carbon), not aniline. (B) Hoffmann bromamide of benzamide (KOH/Br2) removes one carbon and gives aniline. (C) NaBH4 does NOT reduce the aromatic nitro group, so no aniline. (D) Acid hydrolysis of acetanilide gives aniline. So aniline forms only in B and D. Answer: (B).
Solved Amines NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Which preparation methods give a primary amine in NEET Chemistry?
Reduction of nitro compounds (Sn/HCl, H2/Ni), reduction of nitriles (LiAlH4, H2/Ni), reduction of amides (LiAlH4), Gabriel phthalimide synthesis, Hoffmann bromamide degradation, and ammonolysis of alkyl halides (excess NH3). All put nitrogen on exactly one carbon.
Which method does NOT give a primary amine?
Reduction of an isocyanide (R-NC) gives a SECONDARY amine (R-NH-CH3), not a primary amine. This is the classic NEET trap.
Which method gives the PUREST primary amine?
Gabriel phthalimide synthesis gives a pure 1° amine with no 2° or 3° mixture, because nitrogen can carry only one alkyl group. But it fails for aryl amines like aniline.
Do nitrile reduction and Hoffmann bromamide change the carbon count?
Yes. Nitrile reduction (R-CN → R-CH2NH2) ADDS one carbon. Hoffmann bromamide (R-CONH2 → R-NH2) REMOVES one carbon. Both give 1° amines.
Why is this concept important for NEET?
NEET repeatedly asks 'which reaction gives / does not give a primary amine.' Knowing the carbon-count change and the isocyanide trap lets you answer these direct-recall questions in seconds.
