Question

Natural rubber has :

• A. All trans-configuration
• B. Alternate cis- and trans-configuration
• C. Random cis- and trans-configuration
• D. All cis-configuration

Answer 1

The Correct Option is D

The question is regarding the structural configuration of natural rubber. To determine the correct answer, we need to understand the basic structure of natural rubber.

Natural rubber is composed of polyisoprene, which is a polymer of the monomer isoprene (C₅H₈). In natural rubber, these isoprene units are linked in a polymer chain that predominantly exhibits a specific stereochemistry.

The stereochemistry of natural rubber is characterized by all cis-configurations. This means that all the double bonds in the isoprene units of natural rubber are in the cis configuration. The cis configuration refers to the arrangement where the substituent groups attached to the double-bonded carbon atoms are on the same side.

Explanation of Options:

1. All trans-configuration: Incorrect. This configuration is found in synthetic rubbers like gutta-percha.
2. Alternate cis- and trans-configuration: Incorrect. Natural rubber does not exhibit alternating configurations.
3. Random cis- and trans-configuration: Incorrect. The configuration is not random and is predominantly cis in natural rubber.
4. All cis-configuration: Correct. Natural rubber has this structural arrangement, making the polymer chains flexible and elastic.

Therefore, the correct answer is All cis-configuration.

Natural rubber's cis configuration is crucial for its elasticity, which is why it is widely used in making tires, gloves, and various elastic products.