Which of the following reaction(s) is/are of $S_{N} 2$ mechanism?

Finkelstein reaction:

C H_{3} - X + N a I D r y a c e t o n e - ------ \to C H_{3} I + N a X

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Swarts reaction:

C H_{3} - B r + A g F Δ - \to C H_{3} F + A g B r

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Reaction of HI with ether:

C H_{3} - O - C H_{3} + 2 H I \to 2 C H_{3} I + H_{2} O

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Reaction of diazonium salt with water:

(C H_{3})_{2} C H - N_{2}^{+} X^{-} + H_{2} O \to (C H_{3})_{2} C H - O H + N_{2} ↑ + H X

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Solution

The correct option is C Reaction of HI with ether:
$C H_{3} - O - C H_{3} + 2 H I \to 2 C H_{3} I + H_{2} O$
Finkelstein and Swarts reactions favour $S_{N} 2$ reaction when their substracte is a primary alkyl halide.

Finkelstein reaction:
$C H_{3} - X + N a I D r y a c e t o n e - ------ \to S_{N} 2 C H_{3} I + N a X$

Swarts reaction is for the preparation of alkyl fluorides. Reagents used in this reaction are $A g F, S b F_{3}, C O F_{2}, H g_{2} F_{2}$

$C H_{3} - B r + A g F Δ - - \to S_{N} 2 C H_{3} F + A g B r$

Reaction of HI with ether follows $S_{N} 2$ reaction where the $I^{-}$ will attack the carbon bearing oxonium ion from the back by a concerted reaction.
$C H_{3} - O - C H_{3} + 2 H I \to 2 C H_{3} I + H_{2} O$

Reaction of diazonium salt with water follows $S_{N} 1$ reaction due to the leaving property of $N_{2}$ and forms a carbocation intermediate.

$(C H_{3})_{2} C H - N_{2}^{+} X^{-} + H_{2} O \to (C H_{3})_{2} C H - O H + N_{2} ↑ + H X$

Thus, (a), (b) and (c) follows $S_{N} 2$ reaction mechanism.

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