Chemistry - Halogen Derivative Question with Solution | TestHub

Explanation:

Evaluate stereochemical outcomes of alcohol substitution reactions.

Concept:

This question is based on ${\mathrm{S}}_{\mathrm{N}}2$ vs ${\mathrm{S}}_{\mathrm{N}}\mathrm{i}$ mechanisms.

Solution:

Nucleophilic substitution of alcohols may occur with retention, inversion, or racemization depending on the reagent and reaction conditions.

reagent and reaction conditions .

▪ SOCl₂   (without pyridine): Proceeds via the S_Ni mechanism , leading to retention of configuration .

▪ SOCl₂   with pyridine: Follows an S_N2 mechanism , resulting in inversion of configuration .

▪ PCl₃   (with or without pyridine): Proceeds via S_N2 , giving inversion of configuration .

▪ NaI / H₃PO₄   or HI: Substitution occurs via carbocation formation, so racemization and possible rearrangement are expected.

Evaluation of the given cases:

(i) SOCl₂ : Retention observed (Cl on the same side as OH) — Correct .

(ii) SOCl₂   + pyridine: Inversion observed (Cl on the opposite side) — Correct .

(iii): Racemization expected, but only a single configuration is shown — Incorrect .

(iv) PCl₃  + pyridine: Inversion observed — Correct .

(v) Racemization expected, but only a single configuration is shown — Incorrect

Final Answer: 3