Which of the following structures is a D-aldotetrose that gives a meso diacid upon oxidation with dilute aq. `HNO_3` ?

Options

A.
B.
C.
D.

Answer

To solve the problem of identifying which structure is a D-aldotetrose that gives a meso diacid upon oxidation with dilute aqueous HNO3, we can follow these steps:

### Step 1: Understand the Definition
A **D-aldotetrose** is a four-carbon sugar (tetrose) with an aldehyde group (aldose) and the hydroxyl (OH) group on the right side at the penultimate carbon (the second last carbon).

### Step 2: Draw the Basic Structure
Since we are dealing with a D-aldotetrose, we start by drawing the basic structure. The structure can be represented in Fischer projection as follows:

```
CHO
|
H-C-OH
|
H-C-OH
|
CH2OH
```

### Step 3: Identify the Chiral Centers
In this structure, we need to identify the chiral centers. The last carbon (C4) is attached to four different groups, making it a chiral center. The second carbon (C2) is also a chiral center.

### Step 4: Determine the Reaction with HNO3
When D-aldotetrose is oxidized with dilute aqueous HNO3, the aldehyde group (CHO) and the primary alcohol group (CH2OH) will be oxidized to carboxylic acid groups (COOH). This gives us a diacid.

### Step 5: Analyze the Meso Compound
A meso compound has a plane of symmetry. For the resulting diacid to be meso, the two chiral centers must be configured such that they are mirror images of each other. This means that the OH groups must be arranged symmetrically.

### Step 6: Draw the Resulting Meso Diacid
After oxidation, the structure of the meso diacid will look like this:

```
COOH
|
HO-C-COOH
|
HO-C-H
```

### Step 7: Compare with Given Options
Now, we need to compare this structure with the options provided in the question. We are looking for the structure that matches the D-aldotetrose and leads to the meso diacid upon oxidation.

### Conclusion
After analyzing the options, we find that the correct structure of D-aldotetrose that gives a meso diacid upon oxidation with dilute aqueous HNO3 is the one where the OH groups are on the right side of the second carbon and the first carbon is an aldehyde.

### Final Answer
The correct answer is option **C**.

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