Question

What do Grignard reagents do?

Answer 1

Enable `C-C` bond formation in organic chemistry.

Explanation:

The list of `C-C` bond forming reactions is quite small. Treatment of a hydrocarbyl halidie, of various identity, with metallic magnesium can result in the formation of an organometallic reagent in which the ipso carbon has carbanionic character:

`R-X +MgrarrR-MgX`

`R-MgX-=R^(delta-)-""^(delta+)MgX`

Of course there are some restrictions on the starting halide, and the reaction must be performed in dry ether or in a non-protic solvent. This so-called Grignard reagent reacts (usually quantitatively) with carbonyls, ketones and aldehydes, to allow formation of tertiary and secondary alcohols after work up.

`R-MgX + R'C(=O)R''rarrR'R''C(-OMgX)R`

By simply pouring the Grignard onto dry ice, we get a carboxylate salt that gives a carboxylic acid upon aqueous workup:

`R-MgX + CO_2rarrRC(=O)O^(-)""^(+)MgX`

These reactions are usually very easy to perform and will tolerate many (non-protic) functionalities. The carbon chain can be extended by 2 carbons if the Grignard is treated with ethylene oxide.