Question

Which is the most effective ion in an $S{N}^2$ displacement on methyl bromide?

• A. $C_2{H}_5{O}^{\ominus }$
• B. $\stackrel{\ominus }{\mathrm{OH}}$
• C. $C_6{H}_5{O}^{\ominus }$
• D. $C{H}_{3}CO{O}^{\ominus }$

Answer 1

Answer: (A)

More the nucleophilic character, more is the $S{N}^2$ reaction. Basicity and nucleophilicity are same when the nucleophilic centres are same
Acidic order: $HN{O}_3>C{H}_{3}COOH>C_6{H}_{5}OH$ $>H_{2}O>C_2{H}_{5}OH$
Basic and nucleophilic order:
$N{O}_3^{\ominus }<C{H}_{3}CO{O}^{\ominus }<C_6{H}_5{O}^{\ominus }<\stackrel{\ominus }{O}H<C_2{H}_5\stackrel{\ominus }{O}$
Therefore, $C_2{H}_5{O}^{\ominus }$ is the most effective nucleophile among the given nucleophiles