Which of the following is not chiral?

Options

A. 2-Butanol
B. 2,3-Dibromopentane
C. 3-Bromopentane
D. 2-Hydroxypropanoic acid

Answer

To determine which of the given molecules is not chiral, we need to analyze each molecule based on the definition of chirality. A molecule is considered chiral if it has a carbon atom bonded to four different substituents. Let's evaluate each of the four molecules step by step.

### Step 1: Analyze 2-butanol
- **Structure**: 2-butanol has the following structure:
- CH3-CH(OH)-CH2-CH3
- **Chirality Check**: The second carbon (C2) has:
- CH3 (methyl group)
- OH (hydroxyl group)
- CH2CH3 (ethyl group)
- H (hydrogen)
- Since all four substituents are different, **2-butanol is chiral**.

### Step 2: Analyze 2,3-dibromopentane
- **Structure**: 2,3-dibromopentane has the following structure:
- CH3-CH(Br)-CH(Br)-CH2-CH3
- **Chirality Check**: The second carbon (C2) has:
- CH3 (methyl group)
- Br (bromine)
- CH (attached to Br)
- H (hydrogen)
- The third carbon (C3) has:
- Br (bromine)
- CH2 (attached to CH3)
- CH (attached to Br)
- H (hydrogen)
- Both C2 and C3 have four different substituents, so **2,3-dibromopentane is chiral**.

### Step 3: Analyze 3-bromopentane
- **Structure**: 3-bromopentane has the following structure:
- CH3-CH2-CH(Br)-CH2-CH3
- **Chirality Check**: The third carbon (C3) has:
- Br (bromine)
- CH2 (attached to CH2)
- CH2 (attached to CH3)
- H (hydrogen)
- Here, C3 has two identical CH2 groups, meaning it does not have four different substituents. Therefore, **3-bromopentane is not chiral**.

### Step 4: Analyze 2-hydroxypropanoic acid
- **Structure**: 2-hydroxypropanoic acid has the following structure:
- CH3-CH(OH)-C(=O)OH
- **Chirality Check**: The second carbon (C2) has:
- CH3 (methyl group)
- OH (hydroxyl group)
- C(=O)OH (carboxylic acid)
- H (hydrogen)
- Since all four substituents are different, **2-hydroxypropanoic acid is chiral**.

### Conclusion
From the analysis, we find that:
- 2-butanol: Chiral
- 2,3-dibromopentane: Chiral
- 3-bromopentane: Not chiral
- 2-hydroxypropanoic acid: Chiral

Thus, the molecule that is **not chiral** is **3-bromopentane**.