Which statement best describes a Grignard reaction?

Which statement best describes a Grignard reaction?

• A. Reaction of alkyl or aryl magnesium halides with carbonyl compounds to form alcohols after aqueous workup
• B. Hydrogenation of alkanes
• C. Oxidation of primary alcohols to aldehydes
• D. Nucleophilic substitution on alkyl halides to give alcohols

Answer: (A)

Grignard reagents, which are alkyl or aryl magnesium halides, act as nucleophiles toward carbonyl compounds. When they attack a carbonyl, the carbonyl carbon forms a new C–C bond, and the oxygen becomes an alkoxide coordinated to magnesium. After aqueous workup, this alkoxide is protonated to give an alcohol. The amount of substitution on the carbonyl controls the type of alcohol formed: formaldehyde gives primary alcohols, aldehydes give secondary alcohols, and ketones give tertiary alcohols. This is exactly what the statement describes. The other options describe processes that aren’t characteristic of Grignard reactions: hydrogenation of alkanes is not involved with Grignard reagents; oxidation of primary alcohols to aldehydes is a different oxidation process; and nucleophilic substitution on alkyl halides to give alcohols isn’t how Grignard reagents behave—they’re typically used to add to carbonyls rather than to substitute halides.

Grignard reagents, which are alkyl or aryl magnesium halides, act as nucleophiles toward carbonyl compounds. When they attack a carbonyl, the carbonyl carbon forms a new C–C bond, and the oxygen becomes an alkoxide coordinated to magnesium. After aqueous workup, this alkoxide is protonated to give an alcohol. The amount of substitution on the carbonyl controls the type of alcohol formed: formaldehyde gives primary alcohols, aldehydes give secondary alcohols, and ketones give tertiary alcohols. This is exactly what the statement describes.

The other options describe processes that aren’t characteristic of Grignard reactions: hydrogenation of alkanes is not involved with Grignard reagents; oxidation of primary alcohols to aldehydes is a different oxidation process; and nucleophilic substitution on alkyl halides to give alcohols isn’t how Grignard reagents behave—they’re typically used to add to carbonyls rather than to substitute halides.