Bondline / Reactions

Cyanohydrin formation

Cyanide attacks the carbonyl carbon (at about 107°, the Bürgi–Dunitz angle); the alkoxide is then protonated by HCN, regenerating cyanide.

Carbonyl addition · 2 steps

Conditions

HCN with a little KCN or NaCN as catalyst.

Mechanism in 2 steps

Red curly arrows show where each pair of electrons moves.

NONO−HN++
Step 1Cyanide attacks the δ+ carbonyl carbon; the π electrons move onto oxygen.
NO−HNNOHNHCN++
Step 2The alkoxide takes a proton from HCN, giving the cyanohydrin and a new cyanide ion.

About carbonyl addition reactions

The carbon of a C=O is δ+, so nucleophiles attack it and the π electrons move onto oxygen. Weak nucleophiles often need acid to activate the carbonyl first.

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