How many fractions will be obtained on fractional distillation of mixture of all dimethyl cyclopentance?

Answer

To determine how many fractions will be obtained from the fractional distillation of a mixture of all dimethyl cyclopentanes, we can follow these steps:

### Step 1: Identify the Possible Isomers
We need to identify all the possible dimethyl cyclopentane isomers. Dimethyl cyclopentane can have different arrangements of the two methyl groups on the cyclopentane ring.

1. **1,1-Dimethylcyclopentane**: Both methyl groups are attached to the same carbon.
2. **1,2-Dimethylcyclopentane**: One methyl group is attached to one carbon, and the other methyl group is attached to an adjacent carbon.
3. **1,3-Dimethylcyclopentane**: One methyl group is attached to one carbon, and the other methyl group is attached to the carbon two positions away.
4. **1,4-Dimethylcyclopentane**: One methyl group is attached to one carbon, and the other methyl group is attached to the carbon directly opposite.

### Step 2: Count the Unique Isomers
Now we need to determine how many of these isomers are unique and whether they can exist as enantiomers.

- **1,1-Dimethylcyclopentane**: This is not chiral.
- **1,2-Dimethylcyclopentane**: This can exist as two enantiomers (R and S forms).
- **1,3-Dimethylcyclopentane**: This can also exist as two enantiomers (R and S forms).
- **1,4-Dimethylcyclopentane**: This is not chiral.

### Step 3: Calculate Total Unique Isomers
From the analysis:
- 1,1-Dimethylcyclopentane: 1 form
- 1,2-Dimethylcyclopentane: 2 forms (enantiomers)
- 1,3-Dimethylcyclopentane: 2 forms (enantiomers)
- 1,4-Dimethylcyclopentane: 1 form

So, the total number of unique isomers is:
1 (from 1,1) + 2 (from 1,2) + 2 (from 1,3) + 1 (from 1,4) = 6 unique isomers.

### Step 4: Determine Fractions in Fractional Distillation
In fractional distillation, we can separate these isomers based on their boiling points. However, since enantiomers cannot be separated by this method, we consider them as one fraction each.

Thus, the fractions we can obtain from the distillation are:
- 1 fraction for 1,1-Dimethylcyclopentane
- 1 fraction for the pair of 1,2-Dimethylcyclopentane (R and S)
- 1 fraction for the pair of 1,3-Dimethylcyclopentane (R and S)
- 1 fraction for 1,4-Dimethylcyclopentane

### Final Count of Fractions
So, the total number of fractions obtained from the fractional distillation of the mixture of all dimethyl cyclopentanes is:
1 + 1 + 1 + 1 = 4 fractions.

### Conclusion
The answer is that **4 fractions** will be obtained from the fractional distillation of a mixture of all dimethyl cyclopentanes.

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