When the following aldohexose exists in its D-configuration, the total number of stereoisomers in its pyranose form is.
`OHC-CH_(2)-underset(OH)underset("| ")"CH"-underset(OH)underset("| ")"CH"-underset(OH)underset("| ")"CH"-CH_(2)-OH`

Explanation

To determine the total number of stereoisomers for the given aldohexose in its D-configuration when it exists in its pyranose form, we can follow these steps:

### Step 1: Identify the Structure of D-Aldohexose
The structure of D-aldohexose can be represented as follows:
- The carbon chain has an aldehyde group (CHO) at one end and a hydroxymethyl group (CH2OH) at the other end.
- The configuration of D-aldohexose indicates that the hydroxyl (OH) group on the penultimate carbon (the second last carbon) is on the right side.

### Step 2: Cyclization to Form Pyranose
When D-aldohexose cyclizes, it forms a six-membered ring (pyranose form). This occurs when the aldehyde group reacts with one of the hydroxyl groups, typically the one on the fifth carbon.

### Step 3: Identify Chiral Carbons
In the pyranose form, we need to identify the chiral centers:
1. **First Carbon (C1)**: This is the anomeric carbon formed from the aldehyde. It is chiral.
2. **Second Carbon (C2)**: Not chiral (has two H atoms).
3. **Third Carbon (C3)**: Chiral (four different groups).
4. **Fourth Carbon (C4)**: Chiral (four different groups).
5. **Fifth Carbon (C5)**: Not chiral (has two H atoms).

Thus, we have three chiral centers: C1, C3, and C4.

### Step 4: Calculate the Total Number of Stereoisomers
The total number of stereoisomers can be calculated using the formula:
\[ \text{Total Stereoisomers} = 2^n \]
where \( n \) is the number of chiral centers.

In this case, \( n = 3 \):
\[ \text{Total Stereoisomers} = 2^3 = 8 \]

### Conclusion
The total number of stereoisomers in the pyranose form of the given D-aldohexose is **8**.

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