Conjugated carbonyls have ___________ electrophilic carbons

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Question restatement: Conjugated carbonyls have ___________ electrophilic carbons. Answer options: 0, 1, 2, 3.

Option 0: '0' electrophilic carbons. This would imply no carbon in the conjugated carbonyl system is susceptible to nucleophilic attack, which contradicts fundamentals of carbonyl reactivity. In conjugated carbonyls, at least the carbonyl carbon remains electrophilic, so 0 is incorrect.

Option 1: '1' electrophilic carbon. While the carbonyl carbon is definitely electrophilic, conjugation introduces another position (the β-carbon) that can behave as electrophilic under certain conditions (e.g., in Michael-type additions). Therefore claiming only one electrophilic center ignores the additional reactive site created by conjugation, making this option incomplete or inaccurate.

Option 2: '2' electrophilic carbons. This aligns with common teaching: conjugated carbonyl systems (like enones) present two electrophilic centers—the carbonyl carbon and the β-carbon of the conjugated system—which can participate in nucleophilic additions or conjugate additions. This is the correct characterization given typical reactivity patterns.

Option 3: '3' electrophilic carbons. Conjugation in these systems does not usually generate three distinct electrophilic carbons; the primary reactive sites are the carbonyl carbon and the β-carbon, with the rest of the framework being less electrophilic under standard conditions. Thus this overcounts the electrophilic centers and is not correct.

Synthesis of reasoning: The key concept is that conjugation extends the reactive manifold beyond a single carbonyl carbon, introducing an additional electrophilic site at the β-position in many conjugated carbonyls. The rest of the carbon framework does not generally present electrophilicity at multiple distinct centers in the same straightforward manner, so 3 would overstate the count and 1 would understate it. The widely accepted count for standard conjugated carbonyls is two electrophilic carbons, corresponding to option 2.

CHE 008B A01 SS1 2025 Lecture 8 - Conjugated Carbonyls

Conjugated carbonyls have ___________ electrophilic carbons

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