Reaction of a Grignard reagent with an epoxide yields what type of product?

• A. Aldehyde
• B. Extended alcohol after workup
• C. Ketone
• D. Vicinal diol

Answer: (B)

Grignard reagents open epoxides through a straightforward SN2‑type attack, acting as a strong nucleophile to attack the less substituted carbon of the three-membered ring. This ring opening yields an alkoxide on the more substituted carbon that is coordinated to MgX. When you perform the workup with acid, that alkoxide is protonated to give an alcohol. The carbon framework of the epoxide is thus extended by the Grignard’s R group, producing an extended alcohol after workup. This is distinct from forming an aldehyde or ketone (which happens when a Grignard reacts with carbonyl compounds) or creating a vicinal diol (which would require different steps). So the product is an extended alcohol after workup.