Meso form of tartaric acid is –

Options

A. Dextorotatory
B. Laevorotatory
C. Neither Laevo nor dextro rotatory due to internal compensation
D. A mixture of equal quantities of dextro and leavo rotatory forms

Answer

To determine the meso form of tartaric acid, we can follow these steps:

### Step 1: Understand the Structure of Tartaric Acid
Tartaric acid is a naturally occurring organic acid with the formula C4H6O6. It has two carboxylic acid groups (-COOH) and two hydroxyl groups (-OH) attached to a carbon backbone. The structure can be represented as follows:

```
HOOC
|
C
/ \
OH C
|
HOOC
```

### Step 2: Identify Chiral Centers
In tartaric acid, there are two chiral centers. A chiral center is a carbon atom that has four different substituents. In the case of tartaric acid, both chiral centers are attached to different groups:

1. The first chiral carbon has -OH, -COOH, -H, and the other carbon as substituents.
2. The second chiral carbon has -OH, -COOH, -H, and the other carbon as substituents.

### Step 3: Determine the Meso Form
A meso compound is a type of stereoisomer that has multiple chiral centers but is superimposable on its mirror image due to an internal plane of symmetry.

For tartaric acid, if we arrange the two hydroxyl groups (-OH) on the same side (either both above or both below the plane of the molecule), we can find a plane of symmetry. This arrangement leads to the following structure:

```
HOOC
|
C
/ \
OH C
|
HOOC
```

In this structure, if we draw a line (the plane of symmetry) through the molecule, the upper half is a mirror image of the lower half.

### Step 4: Confirm Optical Inactivity
Due to the presence of the plane of symmetry, the meso form of tartaric acid does not rotate plane-polarized light. This is because the optical activities of the two halves cancel each other out, resulting in no net rotation. This phenomenon is referred to as "internal compensation."

### Step 5: Conclusion
The meso form of tartaric acid is optically inactive because of the internal compensation caused by the plane of symmetry. Therefore, the correct answer is that the meso form of tartaric acid is neither dextrorotatory nor levorotatory.