Alkyl Halides - Result Question 42
####42. List-I contains reactions and List-II contains major products.
Q. $> _{ONa}$
Match each reaction in List-I with one or more products in List-II and choose the correct option.
(2018 Adv.)
(a) $P \rightarrow 1,5 ; Q \rightarrow 2 ; R \rightarrow 3 ; S \rightarrow 4$
(b) $P \rightarrow 1,4 ; Q \rightarrow 2 ; R \rightarrow 4 ; S \rightarrow 3$
(c) $P \rightarrow 1,4 ; Q \rightarrow 1,2 ; R \rightarrow 3,4 ; S \rightarrow 4$
(d) $P \rightarrow 4,5 ; Q \rightarrow 4 ; R \rightarrow 4 ; S \rightarrow 3,4$
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Answer:
Correct Answer: 42. $(b)$
Solution:
For this reaction 1 and 4 are probable products.
Product 1 i.e., $OH _{OH}$ is formed due to substitution while product 4 i.e., 1 is formed due to elimination. A tertiary carbocation i.e, + formed during the reaction. Remember for $3^{\circ}$ carbocation ions elimination product predominates.
For $Q$, i.e. $\chi _{OMe}^{+HBr}$
Correctly matched product for this reaction is 2 i.e., $>Br$. The reaction proceeds as
$$ \searrow _{OMe}+HBr \rightarrow MeOH+\searrow _{Br} $$
For $R$ i.e., $\chi _{Br}^{+NaOMe}$
Correctly matched product is 4 i.e., 1 . It is a normal elimination reaction and proceeds as
$$ \chi _{Br}^{+\underset{\begin{array}{c} \text { (Alkali in } \\ \text { alcohol) } \end{array}}{++-} NaOMe} \rightarrow $$
| Column I | Column II | Explanation | |
|---|---|---|---|
| P. | $NaOEt(2)$ | $\overline{O}$ Et (strong nucleophile) causes dehydrohalogenation of $3^{\circ}$ alkyl halide |
|
| Q. | $Ia \rightarrow\rangle$ | $EtBr(3)$ | $3^{\circ}$ butoxide undergoes $S _N$ reaction with $1^{\circ}$ alkyl halide |
$3^{\circ}$ alkyl halide preferes elimination.
For $S$ i.e., $\chi _{ONa}^{+MeBr}$
The correct match is 3 i.e., OMe. The reaction proceeds as
