Chemistry · Haloalkanes And Haloarenes · NEET
Both start from a haloalkane (R-X), but the metal and the product are different. Grignard uses magnesium (Mg) in dry ether and gives an organometallic reagent R-Mg-X (the carbon-metal bond stays). Wurtz uses sodium (Na) in dry ether and joins TWO alkyl halides to give a new alkane R-R with double the carbons. So: Mg = make a reagent; Na = build a bigger alkane. This exact pairing is a common NEET one-mark question.
Ether must be dry (no water) because both the Grignard reagent and the sodium intermediate react instantly with even a trace of water. Water has an acidic H that destroys R-Mg-X (giving R-H, a hydrocarbon) and interferes with Wurtz coupling. Dry ether is a non-reactive solvent that keeps the reactive species safe. If NEET asks 'why anhydrous conditions', the answer is: to avoid moisture that would decompose the reagent.
Wurtz joins two alkyl halides: 2 R-X + 2Na to R-R + 2NaX. When both halides are the SAME (identical R), the product has double the carbons of one halide, so the count is always even (2+2=4, 3+3=6...). To make an ODD-carbon alkane you would need two DIFFERENT halides, which gives a messy mixture of three products and poor yield. That is why NEET says Wurtz is good only for symmetrical, even-carbon alkanes.
n-Heptane has 7 carbons, an ODD number. Wurtz can only cleanly make even-carbon alkanes from two identical halides. To get 7 carbons you must couple two different halides (like a 3-carbon and a 4-carbon halide). But that mixture also self-couples, giving hexane, octane AND heptane together - a low yield of the target. This is the reasoning behind NEET 2020's 'cannot be made in good yield' question.
In R-Mg-X the carbon carries a partial negative charge (a carbanion, R minus), because carbon pulls electrons away from the electropositive Mg. This carbanion is a strong base. Any molecule with even a slightly acidic H (water O-H, alcohol O-H, amine N-H) donates that proton, turning R-Mg-X into R-H (the alkane). That is exactly why the reaction must be kept dry - and why phenylmagnesium bromide plus water gives benzene.
Wurtz-Fittig is a mixed version: an alkyl halide plus an aryl halide (like bromobenzene) with sodium in dry ether gives an alkyl-substituted benzene (an alkylarene). Example: C6H5Br + C2H5Br + 2Na gives ethylbenzene. Plain Wurtz joins two alkyl halides; Wurtz-Fittig joins one alkyl and one aryl halide. NEET 2023 tested this exact ethylbenzene product.
Reaction between acetone and methylmagnesium chloride, followed by hydrolysis, will give:
Which of the following alkanes cannot be made in good yield by the Wurtz reaction?
Hydrocarbon A reacts with bromine by substitution to form an alkyl bromide, which by the Wurtz reaction is converted to a gaseous hydrocarbon containing less than four carbon atoms. A is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A Grignard reagent is an alkyl (or aryl) magnesium halide, R-Mg-X, discovered by Victor Grignard in 1900. It is made by reacting a haloalkane with magnesium metal in dry ether: R-X + Mg to R-Mg-X. The carbon-magnesium bond is covalent but highly polar, giving carbon a carbanion character.
2 R-X + 2Na (dry ether) to R-R + 2NaX. Two alkyl halide molecules couple, forming a new carbon-carbon bond and an alkane with double the number of carbons of one halide.
Because they react with any source of proton. Water, alcohols and amines all have acidic H atoms that convert R-Mg-X into the hydrocarbon R-H, destroying the reagent. So even traces of moisture must be avoided, which is why dry ether is used.
Yes. Bromobenzene with Mg in dry ether gives phenylmagnesium bromide, C6H5MgBr. NEET 2023 used this: bromobenzene to C6H5MgBr, then water gives benzene, because the Grignard is protonated by water's acidic H.
With methanal (HCHO) you get a primary alcohol, with other aldehydes a secondary alcohol, and with ketones a tertiary alcohol. This is why acetone (a ketone) plus a Grignard gives a tertiary alcohol like tert-butyl alcohol.
