An iodo compound, P reacts with sodium acetylide (one mole)...

An iodo compound, $\mathrm{P}$ reacts with sodium acetylide (one mole) in presence of $\mathrm{NH}_{3}$ to give the compound, Q. The latter by a reaction sequence: (I) with $\mathrm{NaNH}_{2}$ in $\mathrm{NH}_{3}$ (II) ethylene oxide followed by hydrolysis gives an saturated, 6 -carbon primary alcohol $\mathrm{R}$. Here the compound P is : (a) $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I}$ (b) $\mathrm{CH}_{3} \mathrm{I}$ (c) $\mathrm{CH}_{3}-\mathrm{CHI}-\mathrm{CH}_{2}-\mathrm{CH}_{3}$ (d) $\mathrm{n}-\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{I}$

An iodo compound, $\mathrm{P}$ reacts with sodium acetylide (one mole) in presence of $\mathrm{NH}_{3}$ to give the compound, Q. The latter by a reaction sequence: (I) with $\mathrm{NaNH}_{2}$ in $\mathrm{NH}_{3}$ (II) ethylene oxide followed by hydrolysis gives an saturated, 6 -carbon primary alcohol $\mathrm{R}$. Here the compound P is :
(a) $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{I}$
(b) $\mathrm{CH}_{3} \mathrm{I}$
(c) $\mathrm{CH}_{3}-\mathrm{CHI}-\mathrm{CH}_{2}-\mathrm{CH}_{3}$
(d) $\mathrm{n}-\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{I}$

Key Concepts

Acetylide Coupling Reaction

This reaction involves the use of a terminal acetylide ion, which is generated by deprotonating a terminal alkyne, to perform an SN2-type nucleophilic substitution on an alkyl halide. This reaction efficiently forms a new carbon–carbon bond and is a crucial strategy in synthetic organic chemistry for building molecular complexity through chain elongation.

Nucleophilic Substitution (SN2) Mechanism

The SN2 mechanism is central to these types of reactions, where a nucleophile attacks an electrophilic carbon in a single concerted step, displacing a leaving group such as iodide. This mechanism is particularly favoured for primary alkyl halides due to lower steric hindrance, making it an essential concept when analyzing reactivity and predicting outcomes in organic synthesis.

Ethylene Oxide Ring Opening Reaction

The reaction with ethylene oxide involves nucleophilic attack on the strained three-membered ring, leading to its ring opening. This transformation is widely used to introduce a two-carbon chain bearing a hydroxyl group after subsequent hydrolysis, which is an important tactic for extending carbon chains and introducing new functional groups in synthesis.

Alkyl Halide Structure and Reactivity

The structure of the alkyl halide significantly influences its reactivity in nucleophilic substitution reactions. For instance, primary halides are more reactive in an SN2 mechanism due to minimal steric hindrance, while secondary and tertiary halides are less favorable. This concept is crucial for selecting appropriate substrates in synthesis reactions to ensure effective formation of the desired carbon–carbon bonds.

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