Q. 17 Match the type of reaction in Group-1 with the most appropriate description in Group-2
Group 1                                                               Group 2
P Hydroboration-oxidation                           1 Electrophilic aromatic substitution
Q Nucleophilic aromatic substitution        2 Oxaphosphetane intermediate
R Wittig reaction                                            3 Meisenheimer complex
S Friedel-Crafts reaction                              4 Anti-Markownikoff’s product
(A) P-2, Q-4, R-1, S-3
(B) P-4, Q-3, R-1, S-2
(C) P-4, Q-3, R-2, S-1
(D) P-2, Q-1, R-4, S-3

Hydroboration-oxidation yields anti-Markovnikov alcohols, while Wittig involves an oxaphosphetane intermediate. The correct matching for this GATE-style question is option (C). This guide breaks down each reaction for exam preparation.

Correct Answer

The right option is (C) P-4, Q-3, R-2, S-1. Hydroboration-oxidation (P) gives the anti-Markovnikov product (4). Nucleophilic aromatic substitution (Q) forms the Meisenheimer complex (3). Wittig reaction (R) proceeds via oxaphosphetane intermediate (2). Friedel-Crafts reaction (S) is electrophilic aromatic substitution (1).​

Hydroboration-Oxidation (P)

This reaction adds water across alkenes in an anti-Markovnikov fashion, placing OH on the less substituted carbon. It follows syn addition with no carbocation rearrangements. Thus, P matches 4 (Anti-Markovnikov’s product).​

Nucleophilic Aromatic Substitution (Q)

Nucleophiles attack electron-deficient aromatics, forming a sigma complex called the Meisenheimer complex. This stabilizes the negative charge during substitution. Q pairs with 3 (Meisenheimer complex).​

Wittig Reaction (R)

Ylides react with carbonyls to form alkenes via a betaine, collapsing to an oxaphosphetane intermediate. The ring opens to yield the alkene and phosphine oxide. R corresponds to 2 (Oxaphosphetane intermediate).​

Friedel-Crafts Reaction (S)

Alkylation or acylation on benzene uses Lewis acids like AlCl3 for electrophilic aromatic substitution. The acylium ion attacks the ring. S links to 1 (Electrophilic aromatic substitution).​

Why Other Options Fail

• (A) Wrongly assigns Wittig to 1 and Friedel-Crafts to 3.

• (B) Mismatches Wittig to 1 and hydroboration to 4 correctly but swaps others.

• (D) Incorrectly places hydroboration with 2 and Wittig with 4.