Which if the following paris of compound is a ring chein isomer ?

Options

A.
B.
C.
D.

Answer

To solve the question of identifying which pair of compounds is a ring-chain isomer, we will follow these steps:

### Step 1: Understand the Concept of Ring-Chain Isomers
Ring-chain isomers are compounds that have the same molecular formula but differ in structure, specifically one being a cyclic compound (ring) and the other being an acyclic compound (open chain).

### Step 2: Analyze Each Option
We will analyze each option provided in the question to check for the presence of both a cyclic and an acyclic structure with the same molecular formula.

### Step 3: Check Option 1
- **Option 1:** Contains four carbons and two -OH groups.
- The cyclic structure here would be cyclo-1,2-butanediol.
- Since both structures do not have the same configuration of hydrogen, they are not isomers.
- **Conclusion:** Not a ring-chain isomer.

### Step 4: Check Option 2
- **Option 2:** Contains a different structure.
- Both structures are not cyclic and do not represent a ring-chain isomer.
- **Conclusion:** Not a ring-chain isomer.

### Step 5: Check Option 3
- **Option 3:** Contains CH2=CH-CH2OH and a cyclic structure.
- The open chain has one degree of unsaturation (due to the double bond).
- The cyclic structure also has one degree of unsaturation.
- Both have the same number of carbons and substituents.
- **Conclusion:** This pair represents a ring-chain isomer.

### Step 6: Check Option 4
- **Option 4:** Contains two cyclic structures.
- We need one cyclic and one acyclic structure for ring-chain isomers.
- **Conclusion:** Not a ring-chain isomer.

### Final Answer
The correct answer is **Option 3**, as it contains a pair of compounds that are ring-chain isomers.

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