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In the reaction of 2-nitropropane [(CH3)2CHNO2] with formaldehyde (HCHO) under basic conditions followed by acidification (NaOH / H+), what is the major product?

1. (CH3)2CH-CH2-O-NO2
2. (CH3)2C(NO2)-CH2OH
3. (CH3)2CH-CO-CHO (an alpha-keto aldehyde derivative)
4. (CH3)2CH-CH(OH)-CH2NO2

Correct answer: (CH3)2C(NO2)-CH2OH

Solution

2-Nitropropane reacts with formaldehyde under basic conditions in a Henry (nitroaldol) reaction. The base abstracts the alpha-hydrogen from C-2 (the only alpha-C bearing the NO2 group), forming a resonance-stabilised carbanion/nitronate. This anion attacks the carbonyl carbon of HCHO to give a beta-nitro alcohol. The product is (CH3)2C(NO2)-CH2OH.

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