See image — Reaction Mechanism Chemistry Question

💡 Solution & Explanation

Concept: Grignard reagents (RMgX) add to carbonyl compounds. CH3MgBr adds a methyl group to the carbonyl carbon. For the product to be a secondary (2°) alcohol, the carbonyl carbon must bear exactly one hydrogen (i.e., it must be an aldehyde carbon with one H and one carbon substituent attached — meaning an aldehyde). A ketone would give a tertiary alcohol (two carbon groups plus the added methyl). A primary aldehyde (RCHO) reacts with CH3MgBr to give R-CH(OH)-CH3, a secondary alcohol. Step 1: Identify carbonyl isomers of C4H8O. The molecular formula C4H8O with degree of unsaturation = (2×4+2-8)/2 = 1, consistent with one C=O. Carbonyl isomers include aldehydes and ketones: - Aldehydes: butanal (CH3CH2CH2CHO), 2-methylpropanal ((CH3)2CHCHO) - Ketones: butanone (CH3COCH2CH3), and cyclic options are excluded as they don't fit simple chain with this formula for a ketone giving 2° alcohol. Step 2: Determine which give a 2° alcohol with CH3MgBr. - Aldehydes (RCHO) + CH3MgBr → R-CH(OH)-CH3 = secondary alcohol ✓ - Ketones (RCOR') + CH3MgBr → tertiary alcohol ✗ So only aldehydes qualify. Step 3: List aldehyde isomers of C4H8O: 1. Butanal: CH3CH2CH2CHO — product is CH3CH2CH2CH(OH)CH3 = pentan-2-ol (no stereocentre making two stereoisomers? The product has a chiral center at C2: R and S enantiomers — but wait, we are counting isomers of C4H8O, not products.) 2. 2-Methylpropanal: (CH3)2CHCHO — product is (CH3)2CHCH(OH)CH3 = 3-methylbutan-2-ol (chiral center, R and S) Step 4: Check for stereoisomers among the C4H8O carbonyl isomers themselves. - Butanal: no stereocentre in the aldehyde itself. - 2-Methylpropanal: no stereocentre. However, re-reading the question: 'including stereoisomer' likely refers to counting stereoisomers of the C4H8O isomers. Among C4H8O aldehyde isomers, there are only 2 structural isomers (butanal and 2-methylpropanal), neither of which has a stereocenter. So the count of carbonyl isomers of C4H8O that give 2° alcohol with CH3MgBr is 2 (butanal and 2-methylpropanal). Therefore, the correct answer is 2.