Which of following is most easily cleaved by `HBr`.

Options

A.
B.
C.
D.

Explanation

To determine which of the given compounds is most easily cleaved by HBr, we need to analyze the structural characteristics of the compounds in question. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
First, we need to identify the compounds provided in the question. Typically, they might include different types of cyclic compounds, such as three-membered, four-membered, or larger rings.

### Step 2: Understand Cleavage by HBr
HBr is a strong acid and can cleave certain types of bonds in organic compounds. The ability of a compound to be cleaved by HBr often depends on the strain in the ring structure.

### Step 3: Analyze Ring Strain
- **Ring Strain**: Compounds with high ring strain are more unstable and thus more likely to undergo cleavage.
- **Three-Membered Rings**: These rings (like cyclopropane) have significant angle strain because the bond angles are much smaller than the ideal tetrahedral angle of 109.5 degrees. This makes them highly reactive and prone to cleavage.

### Step 4: Compare the Rings
- **Three-Membered Rings**: As mentioned, they have high strain and are unstable.
- **Four-Membered Rings**: These have less strain compared to three-membered rings but still have some instability.
- **Larger Rings**: Five-membered and six-membered rings have even less strain and are more stable.

### Step 5: Conclusion
Based on the analysis, the three-membered ring is the most likely to be cleaved by HBr due to its high strain and instability.

### Final Answer
The compound that is most easily cleaved by HBr is the **three-membered ring**.

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