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Grignard reagents appear in three NCERT chapters at once, which is why they are tested so often: haloalkanes, alcohols, and aldehydes and carboxylic acids. If you see them as one idea, a carbon nucleophile that also behaves as a strong base, the questions get much easier. This post covers what Grignard reagents make, how to plan a synthesis backwards, and the traps examiners set.
Where are Grignard reagents in the syllabus?
The JEE (Main) 2026 syllabus and the NEET (UG) 2026 syllabus both list "Grignard reagent" among the important reactions of aldehydes and ketones. The JEE (Advanced) 2026 brochure lists "Grignard reactions" under alkyl halides and Grignard reagents under the preparation of carboxylic acids. Check your own year's syllabus.
The reagent is named after Victor Grignard, who shared the 1912 Nobel Prize in Chemistry "for the discovery of the so-called Grignard reagent". NCERT notes that he first reported the reagents in 1900 and used the work for his doctoral thesis in 1901.
What is a Grignard reagent?
Unit 6 of NCERT Class 12 Chemistry Part II describes it as an alkyl magnesium halide, RMgX, made by reacting a haloalkane with magnesium in dry ether. The carbon–magnesium bond is covalent but highly polar, with carbon carrying the extra electron density. That carbon behaves like a carbanion. It attacks electron-poor carbon, and it grabs any acidic proton it finds.
What does a Grignard reagent make?
NCERT's alcohols chapter, Unit 7 of Class 12 Part II, gives the pattern: Grignard adds to the carbonyl group, and hydrolysis of the adduct gives an alcohol. With methanal you get a primary alcohol, with other aldehydes a secondary alcohol, with ketones a tertiary alcohol. The aldehydes and carboxylic acids chapter adds two more: with carbon dioxide (dry ice) followed by acid you get a carboxylic acid, and with a nitrile followed by hydrolysis you get a ketone.
Using CH₃MgBr (methylmagnesium bromide):
HCHO → CH₃CH₂OH, ethanol (primary)
CH₃CHO → CH₃CH(OH)CH₃, propan-2-ol (secondary)
CH₃COCH₃ → (CH₃)₃COH, 2-methylpropan-2-ol (tertiary)
CO₂, then H₃O⁺ → CH₃COOH, ethanoic acid
CH₃CN, then hydrolysis → CH₃COCH₃, propanone
In every case, the new C–C bond joins the Grignard carbon to the carbon that was electron-poor.
Worked example 1: work backwards from the target
Make 2-methylbutan-2-ol, CH₃CH₂C(OH)(CH₃)₂.
It is a tertiary alcohol, so it comes from a ketone plus a Grignard reagent.
The carbon carrying –OH has three groups: CH₃, CH₃ and CH₂CH₃. One of these comes from the Grignard; the other two were on the ketone.
Route A: take away ethyl. Ketone = propanone (CH₃COCH₃), Grignard = CH₃CH₂MgBr.
Route B: take away a methyl. Ketone = butan-2-one (CH₃COCH₂CH₃), Grignard = CH₃MgBr.
Check by counting: route A, 3 + 2 = 5 carbons; route B, 4 + 1 = 5 carbons. Both work. If a question asks for "a" route, either is correct. Our roadmap for organic conversions uses the same backward method for longer chains.
Worked example 2: the hidden proton
NCERT warns that Grignard reagents react with any proton source, and that even water, alcohols and amines are acidic enough to turn them into hydrocarbons. That is why the reaction is run in dry ether.
How many moles of CH₃MgBr does 1 mol of 4-hydroxybutan-2-one, CH₃COCH₂CH₂OH, use up?
The –OH proton reacts first: CH₃MgBr + ROH → CH₄ + ROMgBr. That uses 1 mol.
The ketone then adds a second CH₃MgBr. That uses 1 mol more.
Total: 2 mol, and 1 mol of methane is given off.
The same reasoning explains why you cannot make a Grignard reagent from a haloalkane that already contains –OH, –NH₂ or –COOH: it would destroy itself.
Common traps
Forgetting the hydrolysis step. The addition gives a magnesium alkoxide. You need water or dilute acid to get the alcohol.
Methanal versus other aldehydes. Only methanal gives a primary alcohol.
Water in the "solvent". Grignard + H₂O gives an alkane, R–H. NCERT notes this can even be used to convert a haloalkane to a hydrocarbon.
CO₂ adds one carbon. CH₃MgBr gives ethanoic acid, not methanoic acid.
Esters. At JEE Advanced level you may see an ester react with two equivalents to give a tertiary alcohol with two identical groups. Check whether your syllabus includes this.
For the carbonyl chemistry behind all of this, read our post on aldehydes and ketones. When you have tried a synthesis and want to check each step, the Fermi Problem Library has a step-by-step solver that explains the reasoning rather than printing an answer.
A practice routine
Write the five reactions above with CH₃CH₂MgBr instead of CH₃MgBr, naming each product.
Plan two Grignard routes for each of three tertiary alcohols, and check by counting carbons.
Do three "how many equivalents" questions with molecules that contain –OH, –NH₂ or –COOH.
Mix in two haloalkane substitution questions so you practise choosing the reaction, not just running it.
This week, take one tertiary alcohol from your textbook and write every Grignard route to it.
