Natural rubber has `:`

Options

A. (a) All trans-configuration
B. (b) Alternate cis-and trans-configuration
C. (c) Random cis-and trans-configuration
D. (d) All cis-configuration

Explanation

To answer the question about the configuration of natural rubber, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Composition of Natural Rubber**:
Natural rubber is a polymer made from the monomer isoprene. The specific form of isoprene that is used to make natural rubber is called cis-isoprene.

2. **Identify the Structure of Cis-Isoprene**:
The chemical structure of cis-isoprene (2-methyl-1,3-butadiene) has a double bond between carbon atoms, and the substituents (in this case, the CH2 groups) are on the same side of the double bond. This is what defines it as a "cis" configuration.

3. **Polymerization of Cis-Isoprene**:
When multiple units of cis-isoprene undergo polymerization, they form a long chain polymer. The repeating unit in this polymer is known as cis-1,4-polyisoprene.

4. **Analyze the Configuration in the Polymer**:
In the polymer chain of cis-1,4-polyisoprene, every unit retains the cis configuration. This means that all the double bonds in the polymer maintain the same orientation as in the original cis-isoprene monomer.

5. **Conclusion**:
Since every repeating unit in the natural rubber polymer is in the cis configuration, we conclude that natural rubber has an "all cis configuration".

### Final Answer:
Natural rubber has **all cis configuration** (Option D).

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