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Which one is a nucleophilic substitution reaction among the following?
A
$CH_3CHO + HCN \rightarrow CH_3CH(OH)CN$
B
$CH_3-CH=CH_2 + H_2O \xrightarrow{H^+} CH_3-CH(OH)-CH_3$
C
$RCHO + R'MgX \rightarrow R-CH(OH)-R'$
D
$CH_3-CH_2-CH(CH_3)-CH_2Br + NH_3 \rightarrow CH_3-CH_2-CH(CH_3)-CH_2NH_2$
Detailed Solution
$CH_3CHO + HCN$: $CN^-$ adds to the carbonyl carbon; this is nucleophilic addition.
Propene + water in acid: $H^+$ attacks the double bond first; this is electrophilic addition.
$RCHO + R'MgX$: the carbanion-like R′ adds to the carbonyl carbon; this is nucleophilic addition.
Alkyl bromide + $NH_3$: the nucleophile $NH_3$ attacks the carbon bearing bromine and displaces $Br^-$ as the leaving group; one group is replaced by another, so this is nucleophilic substitution ($S_N2$).
Hence the nucleophilic substitution reaction is the reaction of the alkyl bromide with $NH_3$.
Propene + water in acid: $H^+$ attacks the double bond first; this is electrophilic addition.
$RCHO + R'MgX$: the carbanion-like R′ adds to the carbonyl carbon; this is nucleophilic addition.
Alkyl bromide + $NH_3$: the nucleophile $NH_3$ attacks the carbon bearing bromine and displaces $Br^-$ as the leaving group; one group is replaced by another, so this is nucleophilic substitution ($S_N2$).
Hence the nucleophilic substitution reaction is the reaction of the alkyl bromide with $NH_3$.