Question

In the reaction of a carbonyl compound with silver cyanide, the lone pair of electrons on the nitrogen are the one that attack the carbonyl carbon. But if a carbonyl compound reacts with hydrogen cyanide, the cyanide ions directly attacks the carbonyl carbon. Explain why this happens??​

Answer 1

For Silver cyanide: Silver is more electropositive. Therefore no need for silver cyanide to split into silver ion and cyanide ion, only the lone pair of electrons from nitrogen atom will be attracted to the carbonyl carbon of the aldehyde or ketone.

For hydrogen cyanide: Hydrogen is less electropositive. Therefore hydrogen cyanide splits into hydrogen ion and cyanide ion, since cyanide ion is negative, It will be directly attracted to the carbonyl compound.

Equations: [ considering a ketone and aldehyde ]

RCHO + HCN → RCHCN + H2O

R'COCH3 + AgCN → R'C(CN)CH3 + Ag + H2O

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