JEE Main 2026 Apr 4 Shift 2, Chemistry Q14: Mechanism of Some Important Reactions of Alkenes

JEE Main2026Apr 4, Shift 2Chemistry

Compound (X) is subjected to the sequence of reactions as shown above. Molar mass of the major product (Y) formed is ______ g mol $^{- 1}$ .

(Given molar mass in g mol $^{- 1}$ C: 12, H: 1, O: 16)

A
90
B
118
C
160
D
125

Solution

Trace the transformations step-by-step.

(i) Br $_{2}$ /CHCl $_{3}$ : anti-addition across the vinyl C=C $\to$ Ph–CHBr–CH $_{2}$ Br (vicinal dibromide).

(ii) NaNH $_{2}$ (excess): double dehydrohalogenation (two successive E2 eliminations) gives the terminal alkyne Ph–C $\equiv$ CH, which the excess base deprotonates to the acetylide Ph–C $\equiv$ C $^{-}$ .

(iii) CH $_{3}$ I: the acetylide attacks methyl iodide (S $_{N}$ 2) $\to$ Ph–C $\equiv$ C–CH $_{3}$ (1-phenylpropyne).

(iv) Na / NH $_{3}$ (l): dissolving-metal reduction selectively gives the trans-alkene $\to$ (E)-Ph–CH=CH–CH $_{3}$ , molecular formula C $_{9}$ H $_{10}$ .

Molar mass of C $_{9}$ H $_{10}$ $= 9 \times 12 + 10 \times 1 = 108 + 10 = 118$ g/mol.

Concept behind this question

Mechanism of Some Important Reactions of AlkenesNotes, formulas and examples →

Practice more Chemistry

Concept-wise practice with instant solutions on Fundamenthol.

Start practicing →

JEE Main 2026 Apr 4 Shift 2, Chemistry Q14: Mechanism of Some Important Reactions of Alkenes

Concept behind this question

More previous year questions on Mechanism of Some Important Reactions of Alkenes

Practice more Chemistry