Acid chlorides react with Grignard reagents to yield tertiary alcohols. Two equivalents of Grignard reagent are required. The first equivalent reacts in a typical nucleophilic acyl substitution reaction to give a ketone. This ketone, however, is itself reactive in the Grignard reaction. Thus, the second equivalent adds to the ketone carbonyl carbon. Subsequent protonation yields the tertiary alcohol.

Draw the curved arrows to show the movements of electrons in this step of the mechanism.