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
A
A
B
B
C
C
D
D

Question

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

BlackTom AI · Accepted Answer

Anhydrides are characterized by two acyl (C=O) groups directly connected through an oxygen atom: R–C(=O)–O–C(=O)–R (or a cyclic variant where both carbonyls and the bridging oxygen are part of a ring).

1. Relevant knowledge points and concepts
- An anhydride contains two carbonyls (C=O) joined by an oxygen atom. In a cyclic anhydride those two carbonyls appear next to a single ring oxygen.
- A diketone is two separate ketone carbonyls on carbon atoms (C=O groups) not connected through an oxygen bridge.
- An ester has one carbonyl adjacent to an OR group (R–C(=O)–O–R′) but only a single acyl carbonyl per ester linkage.
- A carboxylic acid has a carbonyl with an OH (R–C(=O)–OH).

2. Step-by-step reasoning using the drawn structure
- The drawn molecule shows two adjacent C=O groups with an oxygen atom linking them in the ring (a five- or six-membered cyclic system). Visually this is the hallmark of a cyclic anhydride: two acyl C=O units connected by an oxygen.
- There is no free –OH on any carbonyl carbon, so there is no carboxylic acid.
- The oxygen that links the two carbonyls is not an ether substituent on a single carbonyl (as in an ester) but the bridging oxygen between two acyl groups — therefore it’s an anhydride rather than a simple ester.
- Although there are two carbonyls present, they are not independent ketone functions (diketone): their carbonyl carbons are part of acyl groups connected by the bridging oxygen (structure fits an anhydride, not two isolated ketones).

3. Calculations
- No numerical calculations are needed; structural identification is based on connectivity.

4. Why the correct answer is correct
- The molecule exactly matches the connectivity R–C(=O)–O–C(=O)–R in a cyclic form, which defines an anhydride. Both carbonyls are linked through a single oxygen atom; this is the defining functional group present.

5. Why the other options are incorrect
- A (diketone): Incorrect because the two carbonyls are bridged by an oxygen (anhydride), not two separate ketone carbonyls on carbons without the bridge.
- B (ester): Incorrect because an ester has one acyl carbonyl attached to one OR group; here two acyls are joined by the oxygen, i.e., an anhydride, not a single ester linkage.
- D (carboxylic acid): Incorrect because there is no –OH attached to a carbonyl carbon in the structure.

Conclusion: The structure contains a cyclic anhydride functional group, so the correct choice is C, which matches the provided answer.

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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