Which of the following compounds is not chiral?

Options

A. 1-Chloropentane
B. 2-Chloropentane
C. 1-Chloro-2-methylpentane
D. 3-Chloro-2-methylepentane

Answer

To determine which of the following compounds is not chiral, we need to analyze the chirality of each compound based on the presence of chiral centers. A chiral center is typically a carbon atom that is bonded to four different groups. Let's examine each compound step by step.

### Step 1: Analyze 1-Chloropentane
1. **Structure**: The structure of 1-chloropentane has the chlorine atom attached to the first carbon of the pentane chain.
2. **Carbon Analysis**:
- **Carbon 1**: Attached to Cl, H, and two other carbon atoms. It has two identical hydrogen atoms, so it is not chiral.
- **Carbons 2-5**: Each of these carbons has at least two identical groups (hydrogens), making them non-chiral as well.
3. **Conclusion**: 1-Chloropentane has no chiral centers.

### Step 2: Analyze 2-Chloropentane
1. **Structure**: The chlorine atom is attached to the second carbon of the pentane chain.
2. **Carbon Analysis**:
- **Carbon 1**: Two hydrogens and two carbons (non-chiral).
- **Carbon 2**: Attached to Cl, a methyl group (−CH3), a propyl group (−C3H7), and one hydrogen. All four groups are different, making this carbon a chiral center.
- **Carbons 3-5**: Each has at least two identical groups, making them non-chiral.
3. **Conclusion**: 2-Chloropentane has one chiral center.

### Step 3: Analyze 1-Chloro-2-methylpentane
1. **Structure**: The chlorine atom is attached to the first carbon, and a methyl group is attached to the second carbon.
2. **Carbon Analysis**:
- **Carbon 1**: Cl, H, and two carbons (non-chiral).
- **Carbon 2**: Attached to Cl, a methyl group, and two identical groups (non-chiral).
- **Carbons 3-5**: Each has at least two identical groups, making them non-chiral.
3. **Conclusion**: 1-Chloro-2-methylpentane has no chiral centers.

### Step 4: Analyze 3-Chloro-2-methylpentane
1. **Structure**: The chlorine atom is attached to the third carbon, and a methyl group is attached to the second carbon.
2. **Carbon Analysis**:
- **Carbons 1 and 2**: Both have at least two identical groups (non-chiral).
- **Carbon 3**: Attached to Cl, a methyl group, a propyl group, and one hydrogen. All four groups are different, making this carbon a chiral center.
- **Carbons 4 and 5**: Each has at least two identical groups, making them non-chiral.
3. **Conclusion**: 3-Chloro-2-methylpentane has one chiral center.

### Final Conclusion
After analyzing all four compounds, we find that **1-Chloropentane** is the only compound that is not chiral, as it has no chiral centers.