JEE PYQ: Hydrocarbons Question 16
Question 16 - 2020 (02 Sep Shift 2)
The major product obtained from E2-elimination of 3-bromo-2-fluoropentane is:
(1) $\text{CH}_3\text{CH}_2-\text{CH}-\text{CH}=\text{CH}_2$ (with Br)
(2) $\text{CH}_3\text{CH}_2\text{CH}=\text{C}(-\text{F})-\text{CH}_3$
(3) $\text{CH}_3-\text{CH}=\text{CH}-\text{CH}-\text{CH}_3$ (with F)
(4) $\text{CH}_3-\text{CH}_2-\text{C}(=\text{CH})-\text{CH}_3$ (with Br)
Show Answer
Answer: (2)
Solution
In E2 elimination, the more acidic $\beta$-hydrogen (due to $-\text{I}$ effect of F) is preferentially removed. Alc. KOH removes Br and the $\beta$-H anti-periplanar to it, giving $\text{CH}_3\text{CH}_2\text{CH}=\text{C}(\text{F})-\text{CH}_3$.
BETA
