Q.What happens when acetyl chloride is treated with excess of CH₃MgI?

A Grignard reagent's nucleophilic alkyl carbon adds across a huge range of polarised functional groups, and (after an H2O/H+ hydrolysis work-up) delivers a different product class depending on exactly what it was quenched with -- this whole reaction family is tested as 'acetone + i) CH3MgI ii) H2O/H+ gives X, what is X?' style questions. Carbonyl compounds, by how substituted they are: formaldehyde (H-CHO) gives a PRIMARY alcohol; any other aldehyde gives a SECONDARY alcohol; a ketone gives a TERTIARY alcohol -- so acetone + CH3MgI, then H2O/H+, gives tert-butanol (2-methyl-2-propanol), not a simple secondary alcohol. Esters, by stoichiometry: ethyl formate + ONE equivalent of RMgX gives an aldehyde, but with EXCESS RMgX the initially-formed aldehyde reacts on with a second equivalent to give a SECONDARY alcohol instead -- so 'ethyl formate + excess RMgX' specifically means the secondary alcohol, R-CH(OH)-R, not the aldehyde. Likewise an acid chloride + RMgX gives a ketone with one equivalent, but a TERTIARY alcohol with exces …