When considering how reactive a Grignard reagent is with a specific molecule, principally, you need to think of the electrophilicity of its functional groups and potential leaving groups. For these two reasons, I list reactivity in the following order:
1. Anhydrides (because of the carbonyl carbon and the carboxylate leaving group)
2. Acyl halides (because of the carbonyl carbon and the halide leaving group)
3. Esters (because of the carbonyl carbon and the alkoxide leaving group [strong base])
4. Epoxides (because of the carbon bonded to oxygen with the alkoxide product)
5. Aldehyes and ketones (in that order because of the carbon chain's electron donation)
Watch out for acid-base reactions with Grignard reagents because they are preferably basic over nucleophilic. Also, keep in mind that when you see a tertiary alcohol, it was most likely synthesized using Grignard reagents.
Apr 22nd, 2015
Come to think of it, you should probably switch 1 and 2.