Cyanide, alkynyl and alkyl anions

Much of synthetic organic chemistry is concerned with the methods of executing and controlling carbon/carbon bond formation. One of the simplest of such reactions involves the addition of a cyanide ion to a carbonyl group. Write the first step in the addition reaction between a cyanide ion and a general ketone, R2C=0. 

The addition of the cyanide anion is slow, but it is followed by the fast addition of a proton, from either HCN or a protic solvent, to form the cyanohydrin. 

It is observed that this reaction requires base catalysis suggest a reason why this may be so. 

The base is needed to form the cyanide anion, because its conjugate acid, HCN, is not a strong enough nucleophile to attack the carbonyl carbon. 

This simple reaction has introduced an extra carbon atom into the original molecule. Furthermore, this extra carbon is contained within a functional group that may be subsequently developed, for instance, by hydrolysis to reveal a carboxylic acid functionality, or by reduction to an amine. This synthetic route is the basis of the Kiliani method for extending the carbon chain of a sugar. 

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