कार्बनिक रसायन

Standard named reactions in organic chemistry:

• Swarts reaction: Heating alkyl chloride/bromide with metallic fluoride (e.g. $\text{AgF}$) yields alkyl fluoride $\rightarrow$ (III)
• Finkelstein reaction: Halogen exchange with $\text{NaI}$ in dry acetone yields alkyl iodide $\rightarrow$ (IV)
• Sandmeyer's reaction: Diazotisation of aniline followed by treatment with cuprous halide $\text{Cu}_2\text{X}_2$ yields aryl halide $\rightarrow$ (I)
• Wurtz reaction: Reaction of alkyl halides with sodium in dry ether produces higher alkanes $\rightarrow$ (II)

Correct match: (A)-(III), (B)-(IV), (C)-(I), (D)-(II).

$\text{S}_\text{N}2$ displacement takes place via backside nucleophilic attack, so steric hindrance around the reaction centre dramatically reduces reactivity:

• $(\text{CH}_3)_3\text{CBr}$ (C): Tertiary alkyl halide, highly hindered transition state (least reactive towards $\text{S}_\text{N}2$).
• $\text{CH}_3\text{CH}_2\text{CH}(\text{Br})\text{CH}_3$ (B): Secondary alkyl halide, moderately hindered.
• $(\text{CH}_3)_2\text{CHCH}_2\text{Br}$ (D): Primary alkyl halide with steric branching at $\beta$-carbon.
• $\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{Br}$ (A): Unhindered primary alkyl halide (most reactive).

Increasing order of $\text{S}_\text{N}2$ reactivity: $(\text{CH}_3)_3\text{CBr (C)} \lt \text{CH}_3\text{CH}_2\text{CH}(\text{Br})\text{CH}_3\text{ (B)} \lt (\text{CH}_3)_2\text{CHCH}_2\text{Br (D)} \lt \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{Br (A)}$.