Which compounds is achiral in the following?

Options

A. 1- chloro-2- methyl pentane
B. 2- chloropentane
C. 1- chloropentane
D. 3- chloro- 2-methyl pentane

Answer

To determine which compound is achiral among the given options, we will analyze each compound for the presence of chiral centers and symmetry.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- 1-chloro-2-methylpentane
- 2-chloro-pentane
- 1-chloro-pentane
- 3-chloro-2-methylpentane

2. **Understanding Chirality**: A compound is considered chiral if it has a chiral center (a carbon atom attached to four different groups) and does not possess a plane of symmetry. If a compound has a plane of symmetry or a center of symmetry, it is achiral.

3. **Analyze 1-chloro-2-methylpentane**:
- Structure:
```
CH3-CH(Cl)-CH(CH3)-CH2-CH3
```
- The second carbon has:
- Chlorine (Cl)
- Methyl group (CH3)
- Two hydrogen atoms (H)
- Since this carbon is attached to two hydrogen atoms, it cannot be a chiral center. Therefore, this compound is **not achiral**.

4. **Analyze 2-chloro-pentane**:
- Structure:
```
CH3-CH(Cl)-CH2-CH2-CH3
```
- The second carbon has:
- Chlorine (Cl)
- Two hydrogen atoms (H)
- One ethyl group (CH2-CH3)
- This carbon is also not a chiral center because it has two identical hydrogen atoms. Thus, this compound is **not achiral**.

5. **Analyze 1-chloro-pentane**:
- Structure:
```
CH3-CH2-CH2-CH2-CH(Cl)
```
- The fifth carbon (where Cl is attached) has:
- Chlorine (Cl)
- Three hydrogen atoms (H)
- This carbon is not a chiral center either, as it has three identical hydrogen atoms. Therefore, this compound is **not achiral**.

6. **Analyze 3-chloro-2-methylpentane**:
- Structure:
```
CH3-CH(CH3)-CH(Cl)-CH2-CH3
```
- The third carbon has:
- Chlorine (Cl)
- Methyl group (CH3)
- One hydrogen (H)
- One ethyl group (CH2-CH3)
- This carbon is a chiral center because it is attached to four different groups. Therefore, this compound is **chiral**.

7. **Conclusion**: After analyzing all the compounds, we find that none of the first three compounds are chiral, but they also do not have a plane of symmetry. However, since they do not possess chiral centers, they are considered achiral. The compound that is achiral among the given options is **1-chloro-2-methylpentane**.

### Final Answer:
The achiral compound is **1-chloro-2-methylpentane**.