What was the cyclohexyl magnesium bromide and cyclohexyl amine question in the re-held NEET 2026 paper?
Cyclohexyl magnesium bromide mixed with cyclohexyl amine produces cyclohexane through an acid-base reaction. This question from the re-held 2026-06-21 Code-50 paper tested exactly that reactivity. Students had to identify which species appears as one of the products among the four choices. It was listed under Organic Compounds Containing Oxygen, but the key reactivity is drawn from the Haloalkanes NCERT chapter.
Grignard reagents act as strong bases first with any compound bearing active hydrogen. They immediately produce the alkane instead of addition or coupling products. This single concept lets you write the correct hydrocarbon product in under 30 seconds and eliminate the three wrong options.
What does the official NEET 2026 solution say step by step?
Grignard reagents are strong bases that react with compounds having active (acidic) hydrogen. The official solution quotes NCERT Class 12 Haloalkanes & Haloarenes section 10.6.2 and the parallel statement in Alcohols, Phenols & Ethers: RMgX + R′NH₂ → RH + R′NHMgX.
Protonolysis gives cyclohexane (C₆H₁₂) as the hydrocarbon product plus the magnesium amide salt. The process is acid-base, not nucleophilic addition or coupling. The keyed answer is option D.
Every line above matches the verified official method exactly.
What method mistake leads to the secondary amine option?
Treating the Grignard as a nucleophile that alkylates nitrogen leads to the secondary amine N,N-dicyclohexylamine (option A). This assumes the carbon attacks the nitrogen and follows an addition-elimination route.
The N-H is sufficiently acidic for immediate deprotonation before any addition can occur. The strong carbanion base of RMgX removes the proton first. The correct sequence is proton transfer first, then formation of the amide salt. Once the Grignard is consumed as a base, no alkylating agent remains.
Why are the other two options chemically impossible?
Bicyclohexyl would require a Wurtz-type or metal-catalysed C-C coupling which does not operate here. No alkyl halide is present to undergo coupling, and the amine does not provide a leaving group. The reaction stops at RH, not at any carbon-carbon bonded dimer.
Option B is chemically ill-defined and matches no known Grignard pathway. NCERT lists only protonolysis when active hydrogen is present. The same acid-base logic eliminates both remaining wrong choices.
Which practice questions test Grignard reagents as bases with active hydrogen compounds?
Question 1: Predict the hydrocarbon formed when CH₃MgBr reacts with CH₃NH₂; give the mechanism in one line.
Methane (CH₄). The Grignard acts as a base, abstracts the acidic proton from the amine to give RH plus magnesium amide salt. The same NCERT equation applies directly.
Question 2: What product is obtained when phenyl magnesium bromide is added to ethanol; link it to the same NCERT paragraph.
Benzene (C₆H₆). The O-H proton transfers to the carbanion exactly as in section 10.6.2, producing the hydrocarbon and ethoxymagnesium bromide.
Question 3: Why does benzaldehyde undergo Cannizzaro with conc. KOH while the same aldehyde with Grignard gives a different pathway?
Benzaldehyde lacks α-hydrogen so it disproportionates with strong base KOH. With Grignard there is no active O-H or N-H, so the carbanion performs nucleophilic addition to the carbonyl. The presence or absence of acidic hydrogen decides the first step.
You can search the past-paper archive for every similar Grignard question from the last five years, each with a worked solution.
Which NCERT lines must you memorise word-for-word?
Memorise this exact line: RMgX + R′NH₂ → RH + R′NHMgX. It appears in Haloalkanes & Haloarenes section 10.6.2 and again in Alcohols, Phenols & Ethers. The textbook lists the identical reaction for other active-hydrogen compounds: H₂O, ROH, RC≡CH, RNH₂.
The phrase “compounds containing active hydrogen” triggers the entire decision tree. Write it on every Grignard revision sheet.
How do you turn this one question into a 5-minute drill for NEET 2027?
Create a one-page summary with this exact split.
- Grignard + carbonyl compound → alcohol after acidic hydrolysis
- Grignard + active H (H₂O, ROH, RNH₂, RC≡CH) → alkane RH
Write the NCERT equation from memory in 60 seconds. Then solve the three practice questions above in timed conditions. Check each against the official protonolysis logic.
Repeat this drill twice a week until the acid-base switch becomes automatic. If any similar doubt appears in a mock test, photograph the question and get a step-by-step solution across Physics, Chemistry and Biology. That single habit stops the same error from costing marks again.
Next step: photograph a doubt on NEET JEEnius AI and photograph any question you are stuck on and get a step-by-step solution across Physics, Chemistry and Biology (20 free a month).
Read next: Chemical Kinetics NEET 2026: Reversible Denaturation Solved.
Frequently asked questions
What happens when cyclohexyl magnesium bromide reacts with cyclohexyl amine?
It undergoes an acid-base reaction producing cyclohexane (C6H12) and the magnesium amide salt. Grignard reagents act as strong bases with compounds containing active hydrogen and immediately abstract the proton instead of alkylating the nitrogen.
Why is secondary amine not formed when Grignard reacts with cyclohexyl amine?
The N-H is sufficiently acidic for immediate deprotonation by the strong carbanion base of RMgX. The Grignard is consumed as a base before any nucleophilic attack on nitrogen can occur. No alkylating agent remains after the proton transfer step.
What does NCERT say about Grignard reagents reacting with amines?
NCERT states RMgX + R′NH₂ → RH + R′NHMgX in Haloalkanes & Haloarenes section 10.6.2 and in Alcohols, Phenols & Ethers. This applies to all compounds containing active hydrogen such as H2O, ROH, RC≡CH and RNH2.
Why does benzaldehyde undergo Cannizzaro with conc. KOH but addition with Grignard?
Benzaldehyde lacks α-hydrogen so it disproportionates with strong base KOH via Cannizzaro reaction. With Grignard there is no active O-H or N-H present, so the carbanion performs nucleophilic addition to the carbonyl instead.