Problem 75 - A Complete Resource Book in Chemistry for JEE Main

Question

The monomer of the polymer (a) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}\) (c) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{C}=\mathrm{C}\left(\mathrm{CH}_{3}\right)_{2}\) (d) \(\mathrm{H}_{2} \mathrm{C}=\mathrm{C}\left(\mathrm{CH}_{3}\right)_{2}\)

Step-by-Step Solution

Answer

The monomer for polymerization is (d) \(\mathrm{H}_{2} \mathrm{C}=\mathrm{C}(\mathrm{CH}_{3})_{2}\).

Step 1: Understanding the Question

We need to identify the correct monomer that can polymerize to form a polymer. Monomers are small molecules that join together in repeating units to form a polymer.

Step 2: Analyzing the Compounds Provided

The question provides four compounds: (a) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCH}_{3}\)(b) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}\)(c) \((\mathrm{CH}_{3})_{2}\mathrm{C}=\mathrm{C}(\mathrm{CH}_{3})_{2}\) (d) \(\mathrm{H}_{2} \mathrm{C}=\mathrm{C}(\mathrm{CH}_{3})_{2}\). Not all compounds with double bonds can form polymers. Typically, simpler alkene structures are more likely to form polymers.

Step 3: Identifying Simple Alkenes

We are looking for a compound with a simple alkene structure, as these are more likely to polymerize efficiently. Simplified alkene chains tend to have terminal double bonds for effective polymerization.

Step 4: Evaluating Each Option

Let's examine each option:- Compound (a) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCH}_{3}\) is a symmetric internal alkene, less likely to form a polymer.- Compound (b) \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CH}_{2}\) is an asymmetric terminal alkene.- Compound (c) \((\mathrm{CH}_{3})_{2}\mathrm{C}=\mathrm{C}(\mathrm{CH}_{3})_{2}\) has a highly substituted internal double bond, hindering polymerization.- Compound (d) \(\mathrm{H}_{2} \mathrm{C}=\mathrm{C}(\mathrm{CH}_{3})_{2}\) has a terminal double bond, making it more appropriate for polymerization.

Step 5: Selecting the Most Suitable Monomer

Given the options, compound (d) \(\mathrm{H}_{2} \mathrm{C}=\mathrm{C}(\mathrm{CH}_{3})_{2}\) is the best candidate for polymerization, as it has the simplest and most reactive terminal double bond, allowing for effective polymer formation.

Key Concepts

Monomers

Monomers are small, single molecules that are the building blocks of polymers. Think of them as individual beads that can be strung together to form a long necklace or a chain, which in this case, is the polymer. Monomers contain specific reactive groups that enable them to connect or "link" to each other during a chemical reaction known as polymerization.

In essence, during polymerization, monomers undergo chemical reactions that lead to the formation of long chains, resulting in macromolecules. The nature and properties of the final polymer depend heavily on the type of monomer used. Therefore, selecting the appropriate monomer is crucial for the resulting polymer's characteristics.

• Monomers are repeat units in a polymer chain.
• The polymer's properties are determined by the type of monomers used.

Understanding monomers is key to discovering how everyday materials like plastics are created.

Alkenes

Alkenes are a type of hydrocarbon that contains at least one carbon-carbon double bond (\(C=C\)). They are unsaturated because they can add more atoms due to the double bond's presence. The reactivity and chemical properties of alkenes make them excellent candidates for polymerization, especially when forming plastics and various synthetic materials.

Alkenes can undergo a type of polymerization known as addition polymerization, where the double bond is opened up, and the carbon atoms form single bonds with other monomer molecules. This process leads to the formation of a long, continuous chain of carbon atoms.

• Alkenes have at least one double bond.
• They undergo addition polymerization by opening their double bonds.

These features of alkenes are exploited to synthesize a wide range of polymers.

Double Bonds

Double bonds are chemical bonds where two electron pairs are shared between two atoms. In the context of alkenes and polymerization, these occur between carbon atoms and are represented as \(C=C\). Double bonds in alkenes are crucial in defining their reactivity, allowing them to participate in polymerization reactions.

The double bond is responsible for the unsaturated nature of alkenes, making them capable of opening and joining with other monomer units. When the double bond opens, each carbon can bond to additional atoms, creating a more extensive polymer chain. This reactivity is manipulated industrially to develop materials with desired properties, such as elasticity or resistance.

• Double bonds impart reactivity to alkenes.
• They enable the formation of polymers in addition reactions.

In polymer chemistry, the significance of double bonds cannot be overstated, as they are pivotal in creating structurally diverse and functional synthetic materials.