Organometallics Grignard reagents and acetylides

The formation of this product need not concern us, hut its nature is important, in that it contains the equivalent of R or Ar , i.e. the alkyl or aryl group has been transformed into its carbanion. Addition of an aldehyde or ketone to the solution of the Grignard reagent allows a nucleophilic addition reaction to occur. The reaction resembles that of 

It should be noted that, on reaction with Grignard reagents, aldehydes will produce secondary alcohols, whereas ketones will form tertiary alcohols. Often forgotten is the possibility of synthesizing primary alcohols by using formaldehyde as the substrate. 

Acetylides are formed by treating terminal acetylenes with a strong base, sodium amide in liquid ammonia being that most commonly employed. 

Acetylenes with a hydrogen atom attached to the triple bond are weakly acidic (pATa about 25) due to the stability of the acetylide anion (see Section 4.3.4), and this anion can then act as a nucleophile. 

It reacts with aldehydes and ketones in the manner expected, and after acidification yields an alcohol. This reaction also extends the carbon chain by 

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