How many diastereomeric forms are possible for 1,2,3 tribsubstituted cyclobutane when all the substituents are identical?

Answer

To determine how many diastereomeric forms are possible for 1,2,3-trisubstituted cyclobutane when all substituents are identical, we can follow these steps:

### Step 1: Understand the Structure
We start with a cyclobutane ring, which consists of four carbon atoms arranged in a square-like structure. We need to place identical substituents (let's denote them as R) on three of the four carbons.

**Hint:** Visualize the cyclobutane structure and the positions of the substituents.

### Step 2: Identify Substituent Positions
The substituents can be placed on the 1st, 2nd, and 3rd carbon atoms of the cyclobutane. The 4th carbon will remain unsubstituted.

**Hint:** Number the carbons in the cyclobutane ring to keep track of where the substituents are placed.

### Step 3: Determine Possible Configurations
We can arrange the three identical substituents in different configurations relative to the plane of the ring. The configurations can be:
1. All three substituents above the plane.
2. Two substituents above the plane and one below.
3. One substituent above the plane and two below.
4. All three substituents below the plane.

**Hint:** Remember that diastereomers are not mirror images of each other.

### Step 4: Analyze the Configurations
1. **All Above:** This is one configuration.
2. **Two Above, One Below:** This is a second configuration.
3. **One Above, Two Below:** This is a third configuration.
4. **All Below:** This configuration is a mirror image of the first configuration (all above), thus it does not count as a new diastereomer.

**Hint:** Check if any configurations are mirror images of each other.

### Step 5: Count the Distinct Diastereomers
From the configurations analyzed:
- Configuration 1: All above (1)
- Configuration 2: Two above, one below (2)
- Configuration 3: One above, two below (3)

Since the configuration where all substituents are below is a mirror image of the configuration where all are above, it does not count as a new diastereomer.

Thus, the total number of distinct diastereomeric forms is **3**.

**Final Answer:** There are 3 diastereomeric forms possible for 1,2,3-trisubstituted cyclobutane when all substituents are identical.