Write down functional isomers of a carbonyl compound with molecular formula $C_3H_6O$. Which isomer will react faster with $HCN$ and why? Explain the mechanism of the reaction also. Will the reaction lead to the completion with the conversion of whole reactant into product at reaction conditions? If a strong acid is added to the reaction mixture what will be the effect on concentration of the product and why?

(N/A) The functional isomers of $C_3H_6O$ containing a carbonyl group are propanal $(CH_3CH_2CHO)$ and propanone $(CH_3COCH_3)$.
$(a)$ Propanal $(CH_3CH_2CHO)$ reacts faster with $HCN$ than propanone $(CH_3COCH_3)$ because propanal is less sterically hindered and more electrophilic due to the presence of only one electron-donating alkyl group compared to two in propanone.
$(b)$ The reaction mechanism involves the nucleophilic attack of the cyanide ion $(CN^-)$ on the carbonyl carbon,followed by protonation.
$HCN + OH^- \rightleftharpoons CN^- + H_2O$
$R_2C=O + CN^- \rightleftharpoons R_2C(O^-)CN$
$R_2C(O^-)CN + H_2O \rightleftharpoons R_2C(OH)CN + OH^-$
$(c)$ The reaction is reversible and does not go to completion; it reaches an equilibrium state.
$(d)$ If a strong acid is added,it reacts with the $CN^-$ ions to form $HCN$,thereby decreasing the concentration of the nucleophile $(CN^-)$. This shifts the equilibrium to the left,decreasing the concentration of the cyanohydrin product.