The number of asymmetric carbon atom/s in lactic acid is /are_______.

Options

A. one
B. two
C. three
D. zero

Answer

To determine the number of asymmetric carbon atoms in lactic acid, we will follow these steps:

### Step 1: Understand the Structure of Lactic Acid
Lactic acid has the molecular formula \( \text{C}_3\text{H}_6\text{O}_3 \). Its structural formula can be represented as:
\[ \text{CH}_3\text{CHOH}\text{COOH} \]

### Step 2: Identify the Carbon Atoms
In the structure of lactic acid, we have three carbon atoms:
1. The first carbon (C1) is part of the methyl group (\( \text{CH}_3 \)).
2. The second carbon (C2) is the carbon attached to the hydroxyl group (\( \text{CHOH} \)).
3. The third carbon (C3) is part of the carboxylic acid group (\( \text{COOH} \)).

### Step 3: Check Each Carbon for Chirality
To determine if a carbon atom is asymmetric (chiral), it must meet two conditions:
1. It must be sp³ hybridized (forming four sigma bonds).
2. It must be bonded to four different groups or atoms.

#### Analyzing Each Carbon:
- **C1 (from \( \text{CH}_3 \))**:
- It forms four sigma bonds (three with hydrogen and one with C2).
- All groups attached are not different (three hydrogens are identical).
- **Conclusion**: Not chiral.

- **C2 (from \( \text{CHOH} \))**:
- It forms four sigma bonds (one with C1, one with C3, one with -OH, and one with -H).
- The groups attached are: \( \text{CH}_3 \), \( \text{OH} \), \( \text{COOH} \), and \( \text{H} \) (all different).
- **Conclusion**: Chiral (asymmetric carbon).

- **C3 (from \( \text{COOH} \))**:
- It forms three sigma bonds (one with C2, one with -OH, and one with the carbonyl oxygen).
- It does not form four sigma bonds, as it has a double bond with oxygen.
- **Conclusion**: Not chiral.

### Step 4: Count the Asymmetric Carbons
From the analysis, we find that only C2 is chiral. Therefore, the number of asymmetric carbon atoms in lactic acid is **1**.

### Final Answer
The number of asymmetric carbon atom/s in lactic acid is **1**.

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