Typically a strongly basic irreversible nucleophile will add to the C of the C=O , this is known as 1,2-addition .

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Let’s break down the statement and the two selections involved here, since the prompt uses a dropdown format with two parts to choose.

Option 1: 'C of the C=O' — This refers to the carbon atom of the carbonyl group (the carbonyl carbon). In typical nucleophilic additions to aldehydes and ketones, a nucleophile attacks the electrophilic carbonyl carbon rather than the oxygen or other atoms. This aligns with the standard mechanistic picture where the nucleophile donates electron density to the carbonyl carbon, forming a new C–Nu bond and pushing electrons onto the oxygen as an alkoxide. Therefore, selecting the carbon of the C=O as the site of attack is correct in describing where the nucleophile adds.

Option 2: '1,2-addition' — In carbonyl chemistry, 1,2-addition (also called direct or nucleophilic addition) refers to the process where the nucleophile adds to the carbonyl carbon (the first atom of the functional group in the addition) and the electrons shift to the oxygen (the second atom involved in the addition). The statement that a strongly basic irreversible nucleophile will add to the carbon of the C=O and that this is known as 1,2-addition is consistent with the conventional nomenclature: the attack occurs at the carbonyl carbon (1) and the resulting negative charge resides on oxygen (2).

Now, consider why the other possibilities would be incorrect if they were framed as distinct options (though they aren’t provided here, this helps anticipate common misinterpretations):
- If someone suggested the attack occurs at the oxygen atom, that would be incorrect for typical nucleophilic additions to carbonyls, because the carbonyl carbon is the electrophilic center and the nucleophile attacks there.
- If someone claimed the process is called 1,4-addition, that would apply to conjugate (Michael) additions to α,β-unsaturated carbonyl compounds, not to straightforward 1,2-addition to a simple carbonyl group; under basic conditions, 1,4-additions are less favored for ordinary carbonyls without conjugation.
- If the statement claimed that a strongly basic nucleophile would not undergo irreversible addition, that would ignore the typical behavior of strong bases or organometallic nucleophiles reacting with carbonyls via rapid, irreversible nucleophilic attack under certain conditions.

In summary, both components—the site of attack being the carbon of the C=O and the overall process being described as 1,2-addition—are coherent with the standard mechanistic understanding of nucleophilic addition to carbonyls under strongly basic conditions.

CHE 008B A01 SS1 2025 Lecture 8 - Conjugated Carbonyls

Typically a strongly basic irreversible nucleophile will add to the C of the C=O , this is known as 1,2-addition .

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