Isoprene units prevail in all the following except

Options

A. Natural rubber
B. Vitamin `A`
C. Terpenes
D. Vitamin `E`

Answer

To solve the question "Isoprene units prevail in all the following except," we will analyze each of the given options to determine whether they contain isoprene units or not.

### Step 1: Understand Isoprene Units
Isoprene is a hydrocarbon with the formula C5H8, and it is the building block of many natural compounds. It is important to identify which of the given options contain isoprene units.

### Step 2: Analyze Each Option
1. **Natural Rubber**:
- Natural rubber is primarily composed of polyisoprene, which is a polymer made up of isoprene units.
- Therefore, natural rubber contains isoprene units.

2. **Vitamin A**:
- Vitamin A is derived from carotenoids and contains structures that include isoprene units. Specifically, it has components like retinal and retinol, which are derived from isoprene.
- Thus, Vitamin A contains isoprene units.

3. **Terpene**:
- Terpenes are a large class of organic compounds produced by various plants. They are built from isoprene units. The simplest type, known as monoterpenes, consists of two isoprene units.
- Therefore, terpenes contain isoprene units.

4. **Vitamin E**:
- Vitamin E is a fat-soluble antioxidant that does not contain isoprene units. It is primarily composed of tocopherols and tocotrienols, which do not have the isoprene structure.
- Hence, Vitamin E does not contain isoprene units.

### Step 3: Conclusion
Based on the analysis, the correct answer to the question "Isoprene units prevail in all the following except" is **Vitamin E**.

### Final Answer
The correct option is **Vitamin E**.

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