(N/A) Aldehydes and ketones can be prepared from Grignard reagents $(RMgX)$ by reaction with nitriles $(R'CN)$ followed by acid hydrolysis.
$1.$ Preparation of Aldehydes:
Reaction of Grignard reagent with hydrogen cyanide $(HCN)$ followed by hydrolysis yields an aldehyde.
$H-C \equiv N + RMgX$ $\rightarrow [R-CH=NMgX]$ $\xrightarrow{H_2O, H^+} R-CHO + NH_3 + Mg(OH)X$
Example: $H-C \equiv N + CH_3MgI$ $\rightarrow CH_3-CH=NMgI$ $\xrightarrow{H_2O, H^+} CH_3CHO + NH_3 + Mg(OH)I$
$2.$ Preparation of Ketones:
Reaction of Grignard reagent with alkyl nitriles $(R'CN)$ followed by hydrolysis yields a ketone.
$R'C \equiv N + RMgX$ $\rightarrow [R'C(R)=NMgX]$ $\xrightarrow{H_2O, H^+} R'COR + NH_3 + Mg(OH)X$
Example: $CH_3C \equiv N + CH_3MgI$ $\rightarrow CH_3C(CH_3)=NMgI$ $\xrightarrow{H_2O, H^+} CH_3COCH_3 + NH_3 + Mg(OH)I$