The functional groups present in the following molecule include A. a diketone B. an ester C. an anhydride D. a carboxylic acid

Question

BlackTom AI · Accepted Answer

An anhydride contains two acyl groups (R–C(=O)–) joined through an oxygen atom, with the general connectivity R–C(=O)–O–C(=O)–R. Key functional-group recognition points: count C=O groups, look for O atoms bridging two carbonyl carbons, and look for OH groups on carbonyl carbons (carboxylic acids).

Step-by-step reasoning:
1. Count carbonyls: the drawn structure shows two C=O groups (two carbonyls) positioned on adjacent parts of the molecule.
2. Examine connectivity of those carbonyls: both carbonyl carbons are bonded to the same oxygen atom (an O atom sits between the two carbonyl carbons). That oxygen is single-bonded to both carbonyl carbons, giving the pattern R–C(=O)–O–C(=O)–R.
3. Check for OH: neither carbonyl carbon bears an –OH group, so there are no carboxylic acid groups (R–C(=O)–OH).
4. Check whether the two carbonyls are simply separate ketones (a diketone): they are not two independent C=O groups on different carbons unconnected by an intervening oxygen; instead they are linked via the bridging oxygen, characteristic of anhydrides.
5. Check whether the structure is a single ester: an ester has only one acyl carbonyl attached to an OR group (R–C(=O)–O–R). Here there are two acyl carbonyls connected through the same oxygen, so it is not a simple ester but an anhydride (which can be thought of as two acyl groups joined by O).

Why C is correct: the molecule fits the R–C(=O)–O–C(=O)–R pattern exactly, the defining feature of an anhydride. Why the others are incorrect: A (diketone) would show two separate C=O groups not bridged by an oxygen; B (ester) would show only one acyl carbonyl attached to an alkoxy substituent, not two acyls joined; D (carboxylic acid) requires an –OH on the carbonyl carbon, which is absent. Therefore the correct answer is C (an anhydride).

The functional groups present in the following molecule include A. a diketone B. an ester C. an anhydride D. a carboxylic acid单项选择题

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