Question

Isoprene is the repeating unit in natural rubber. The structure of isoprene is C=CC(C)=CC a. Give a systematic name for isoprene. b. When isoprene is polymerized, two polymers of the form are possible. In natural rubber, the cis configuration is found. The polymer with the trans configuration about the double bond is called gutta percha and was once used in the manufacture of golf balls. Draw the structure of natural rubber and gutta percha showing three repeating units and the configuration about the carbon-carbon double bonds.

Short answer

a. The systematic name for isoprene is 2-methyl-1,3-butadiene. b. Natural rubber structure (cis configuration): [\(CH_2C(CH_3)C(CH_2CH_3)=CCH_2{-}\) ]\(COO-\) _\( | )_ _\(-C_2H_5\) |\( -C_2H_5\) Gutta percha structure (trans configuration): [ \(CH_2C(CH_3)C(CH_2CH_3)=CCH_2{-}\) ]\(|COO-\) _\( | )_|\(-C_2H_5\) |\( -C_2H_5\)

Step-by-step solution

a. Systematic name for isoprene

To provide a systematic name for isoprene, we need to find the relevant functional groups and their positions. The isoprene chemical structure is: C=CC(C)=CC The first step is to identify the longest carbon chain containing the functional group, which is a double bond (=). In this case, the longest chain is only 4 carbons long. Next, we number the carbons in the chain, starting at the carbon with the double bond, and assign the appropriate suffix for the double bond (-ene). The systematic name for isoprene is 2-methyl-1,3-butadiene.

b. Drawing the structure of natural rubber and gutta percha

When isoprene is polymerized, it can form either natural rubber or gutta percha, depending on the configuration about the carbon-carbon double bonds. Natural rubber has the cis configuration, while gutta percha has the trans configuration. We will show three repeating units for both polymers. 1. Natural Rubber: The polymerization of isoprene can be represented using a single-bonded pair of carbon atoms with the cis configuration, connected to two single repeating units. Natural rubber with three repeating units can be drawn as follows: [\(CH_2C(CH_3)C(CH_2CH_3)=CCH_2{-}\) ]\(COO-\) _\( | )_ _\(-C_2H_5\) |\( -C_2H_5\) The above structure illustrates the cis configuration, with the ethyl and methyl groups on the same side of the double bond. 2. Gutta Percha: The polymerization of isoprene with the trans configuration about the carbon-carbon double bonds can be represented similarly, except the ethyl and methyl groups would be on the opposite sides of the double bond. Gutta percha with three repeating units can be drawn as follows: [ \(CH_2C(CH_3)C(CH_2CH_3)=CCH_2{-}\) ]\(|COO-\) _\( | )_|\(-C_2H_5\) |\( -C_2H_5\) The above structure illustrates the trans configuration, with the ethyl and methyl groups on opposite sides of the double bond.

Key concepts

Systematic Naming

Systematic naming in chemistry allows us to provide precise and universally understood names for chemical compounds. When dealing with isoprene, its systematic name is derived by identifying the structure of the molecule.
The structure of isoprene, as given by its SMILES notation, is C=CC(C)=CC. To determine the systematic name, we first find the longest carbon chain including the double bonds. In this case, it is a chain of 4 carbon atoms.
We then number the chain from the end closest to the functional groups, which are the double bonds in this instance. Thus, starting from the left, we name the compound as "2-methyl-1,3-butadiene". This name tells us:

• There is a four-carbon chain ("butadiene")
• There are two double bonds at carbon 1 and 3
• There is a methyl group attached to carbon 2

Natural Rubber

Natural rubber is a polymer made from the polymerization of isoprene. In the case of natural rubber, the polymerization occurs in a way that the repeated units take on a specific orientation called the cis configuration.
In the cis configuration, the carbon-carbon double bonds are arranged such that the larger substituents on each carbon are on the same side. This results in a kinked shape, contributing to the material's elasticity and resilience.
Natural rubber is harvested from the latex of rubber trees and has numerous applications due to its flexible and durable properties, including in tires, shoes, and various industrial products.
The structural characteristic of natural rubber provides it with the unique property of being able to return to its original shape after being deformed, a valuable trait for many applications.

Gutta Percha

Gutta percha is another polymer similar to natural rubber but with some differences. Like natural rubber, it is also derived from isoprene. However, during its polymerization, isoprene forms a polymer with a trans configuration about the carbon-carbon double bonds.
In the trans configuration, the substituents are on opposite sides of the double bond, resulting in a more linear structure. This linearity imparts different physical properties compared to natural rubber.
Historically, gutta percha was used in the manufacture of golf balls due to its firm texture. Today, its dental applications are well-known, being used as a filling material in endodontics for root canals, thanks to its biocompatibility and firmness.
While gutta percha may not be as elastic as natural rubber, its sturdiness and stability make it suitable for certain specialized applications.

Polymerization

Polymerization is a chemical process that combines small molecules called monomers into a larger, repetitive chain known as a polymer. This process is crucial in forming both natural rubber and gutta percha from isoprene monomers.
During polymerization, the double bonds in isoprene open up and link together, forming long chains. Natural rubber and gutta percha differ based on how these links (or bonds) are configured. This is referred to as the stereochemistry of the polymer.
The nature of the polymerization process—such as in cis for natural rubber and trans for gutta percha—profoundly influences the mechanical and chemical properties of the resulting polymer. These differences highlight how slight changes at the molecular level can lead to different materials with distinct uses.
Understanding polymerization provides insights into the diverse world of synthetic and natural materials and their applications in everyday life.