Which of the following is a chiral molecule?

Options

A. 1-chloro propane
B. 2-chloro propane
C. 1-chloro butane
D. 2-chloro butane

Explanation

To determine which of the given molecules is chiral, we need to identify if any of the molecules contain a chiral carbon atom. A chiral carbon atom is one that is bonded to four different groups or atoms.

### Step-by-Step Solution:

1. **Understand the Definition of Chirality**:
- A molecule is chiral if it has a carbon atom (chiral center) bonded to four different substituents.

2. **Analyze the First Option: 1-Chloropropane**:
- Structure: CH3-CH2-CH2Cl
- The first carbon (C1) has two hydrogen atoms and one chlorine atom, making it not chiral.
- The second carbon (C2) and third carbon (C3) also do not have four different groups.
- **Conclusion**: Not chiral.

3. **Analyze the Second Option: 2-Chloropropane**:
- Structure: CH3-CH(Cl)-CH3
- The second carbon (C2) is bonded to two methyl groups (CH3), one chlorine (Cl), and one hydrogen (H).
- Since C2 has two identical groups (methyl groups), it is not chiral.
- **Conclusion**: Not chiral.

4. **Analyze the Third Option: 1-Chlorobutane**:
- Structure: CH3-CH2-CH2-CH2Cl
- The first carbon (C1) has two hydrogen atoms and one chlorine atom, making it not chiral.
- The other carbons also do not have four different groups.
- **Conclusion**: Not chiral.

5. **Analyze the Fourth Option: 2-Chlorobutane**:
- Structure: CH3-CH(Cl)-CH2-CH3
- The second carbon (C2) is bonded to:
- One chlorine (Cl)
- One hydrogen (H)
- One methyl group (CH3)
- One ethyl group (CH2-CH3)
- Since all four substituents on C2 are different, this carbon is a chiral center.
- **Conclusion**: This molecule is chiral.

6. **Final Answer**:
- The chiral molecule among the options is **2-Chlorobutane**.