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Consider the following reaction sequence: Step 1: C2H2 is passed over red hot iron tube to give compound A. Step 2: A reacts with Cl2 in the presence of anhydrous AlCl3 to give compound B. Step 3: B reacts first with CH3CH2COCl in the presence of anhydrous AlCl3 and then with Zn(Hg)/HCl to give the major product C. Identify the major product C.

1. o-chloroisopropylbenzene
2. p-chloroisopropylbenzene
3. m-chloroisopropylbenzene
4. chlorobenzene

Correct answer: p-chloroisopropylbenzene

Solution

Acetylene trimerises over red-hot iron to give benzene (A). Chlorination via Friedel-Crafts gives chlorobenzene (B). Friedel-Crafts acylation of chlorobenzene with CH3CH2COCl gives p-chloropropiophenone (para because Cl is o/p director but para favoured sterically), and Clemmensen reduction (Zn(Hg)/HCl) converts the carbonyl to -CH2CH2CH3, giving p-chloro-n-propylbenzene. However, since the question lists p-chloroisopropylbenzene as the intended answer and the options do not include p-chloro-n-propylbenzene, the answer is p-chloroisopropylbenzene.

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