Which among the following represents sec-butyl group?

Options

A.
B.
C.
D.

Answer

To determine which structure represents the sec-butyl group, we need to understand the definition of the sec-butyl group and its structural characteristics.

### Step-by-Step Solution:

1. **Understand the Butyl Group**:
The butyl group consists of four carbon atoms. The general formula for a butyl group is C4H9.

2. **Identify the Type of Butyl Group**:
The prefix "sec-" stands for "secondary." A secondary butyl group means that the butyl group is attached to a carbon atom that is connected to two other carbon atoms.

3. **Draw the Structure of Sec-Butyl**:
- The sec-butyl group can be represented as follows:
- Start with a carbon chain of four carbons: C-C-C-C.
- The secondary carbon (the one that connects to two other carbons) is the second carbon in the chain.
- The structure can be drawn as:
```
CH3
|
CH3-CH-CH2-CH3
|
CH2
```
- In this structure, the second carbon is connected to two other carbon atoms (the first and the third carbon), making it a secondary carbon.

4. **Identify the Correct Representation**:
- Look at the options provided in the question and identify which one matches the structure of sec-butyl as described above.

### Conclusion:
The sec-butyl group is represented by the structure where the secondary carbon is bonded to two other carbon atoms, and it can be denoted as CH3-CH(CH3)-CH2-.