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JEE Main 2026 Apr 8 Shift 2, Chemistry Q15: Properties of Alkanes

JEE Main2026Apr 8, Shift 2Chemistry
Q.

n-Butane on monochlorination under photochemical conditions gives an optically active compound "P". "P" on further chlorination gives dichloro compounds.

The number of dichloro compounds obtained (ignore stereoisomers) is :

  1. A

  2. B

  3. C

  4. D

Solution

Identify P. -Butane has possible monochlorination products: 1-chlorobutane (achiral) and 2-chlorobutane (chiral). Since P is optically active, P 2-chlorobutane, CHCHClCHCH.

Replace a second H with Cl at each distinct position on P. The four chemically distinct H-positions are C1, C2 (which already bears Cl), C3, and C4 (where C1 and C4 are now non-equivalent because of the Cl on C2):

(i) 1,2-dichlorobutane (Cl on C1, Cl on C2).

(ii) 2,2-dichlorobutane (second Cl on C2 — geminal).

(iii) 2,3-dichlorobutane (Cl on C2 and C3).

(iv) 1,3-dichlorobutane (note: chlorinating C4 from this molecule actually gives 1,3-dichlorobutane after renumbering, since C2-Cl becomes C2 from the other end).

Ignoring stereoisomers, constitutional dichloro products are obtained.

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