Question

Which of the following would produce enantiomeric products when reacted with methyl magnesium iodide?

• A. Benzaldehyde
• B. Propiophenone
• C. Acetone
• D. Acetaldehyde

Answer 1

The Correct Option is A, B

• Grignard Reaction: Methyl magnesium iodide (CH₃MgI) is a Grignard reagent, which is a strong nucleophile. It reacts with carbonyl compounds (aldehydes and ketones) to form alcohols.
• Chirality: A molecule is chiral if it is non-superimposable on its mirror image (i.e., it has a stereocenter with four different substituents).
• Benzaldehyde (C₆H₅CHO): Reaction with CH₃MgI followed by protonation gives 1-phenylethanol (C₆H₅CH(OH)CH₃). The carbon atom bonded to the OH group is attached to a phenyl group, a methyl group, a hydrogen atom, and an OH group. These are four different groups, so it is a chiral center, creating a pair of enantiomers.
• Propiophenone (C₆H₅C(=O)CH₂CH₃): Reaction with CH₃MgI followed by protonation gives 2-phenylbutan-2-ol (C₆H₅C(OH)(CH₃)CH₂CH₃). The carbon atom bonded to the OH group is attached to a phenyl group, a methyl group, an ethyl group, and an OH group. These are four different groups, so it is a chiral center, creating a pair of enantiomers.
• Acetone (CH₃C(=O)CH₃): Reaction with CH₃MgI followed by protonation gives 2-methylpropan-2-ol ((CH₃)₃COH). The carbon bonded to the OH group is attached to three methyl groups and an OH group. It has two or more identical groups attached to it, so it is *not* chiral.
• Acetaldehyde (CH₃CHO): Reaction with CH₃MgI followed by protonation gives propan-2-ol (CH₃CH(OH)CH₃). The carbon bonded to the OH group is attached to two methyl groups, a hydrogen, and an OH group. It has two or more identical groups attached to it, so it is *not* chiral.

Therefore, only benzaldehyde and propiophenone produce chiral alcohols (and thus enantiomers) upon reaction with methyl magnesium iodide.

Correct Answer: Benzaldehyde, Propiophenone