Purine without ketonic group is

Options

A. adenine
B. adenosine
C. cytidine
D. thymidine

Answer

To determine which purine does not contain a ketonic group, we will analyze the structures of the purines listed in the options: adenine, adenosine, cytidine, and thymidine.

### Step-by-Step Solution:

1. **Identify the Purines**:
- Purines are a class of nitrogenous bases that include adenine and guanine.
- The question asks for a purine without a ketonic group.

2. **Understand Ketonic Groups**:
- A ketonic group (C=O) is a carbonyl group where the carbon atom is bonded to two other carbon atoms. In the context of nitrogenous bases, it refers to a carbonyl group present in the structure.

3. **Draw the Structures**:
- **Adenine**: The structure of adenine is:
```
N
/ \
C C
|| |
N N
| |
C----C
\ /
N
/ \
H H
```
- **Guanine**: The structure of guanine is:
```
N
/ \
C C
|| |
N N
| |
C----C
\ /
N
/ \
O H
```
- In adenine, there is only an amino group (NH2) present, while in guanine, there is both an amino group (NH2) and a ketonic group (C=O).

4. **Analyze the Structures**:
- From the structures, we can see that adenine lacks a ketonic group, while guanine contains one.

5. **Conclusion**:
- Since adenine is the only purine that does not have a ketonic group, the answer to the question is **adenine**.

### Final Answer:
The purine without a ketonic group is **adenine**.