The structure of nylon-6 is
(a) [-(CH2)6-C(=O)-NH-]_n
(b) [-C(=O)-(CH2)5-NH-]_n
(c) [-(CH2)4-C(=O)-N

Q: Why is it called Nylon-6 and not Nylon-7 since the caprolactam ring has 7 members?

The number in the name of a Nylon polymer refers strictly to the number of carbon atoms in the monomer unit, not the total number of atoms in the ring. Caprolactam has 6 carbon atoms and 1 nitrogen atom, making it a 7-membered ring, but it is named Nylon-6 for its 6 carbons.

Q: What is the difference between Nylon-6 and Nylon-6,6?

Nylon-6 is made from a single monomer (caprolactam) that contains 6 carbons. Nylon-6,6 is made from two different monomers (adipic acid and hexamethylenediamine), each of which contains 6 carbons.

Q: Why does the C-N bond break during polymerisation?

The amide bond (C-N) is susceptible to hydrolysis. When heated with water, the water molecule attacks the carbonyl carbon, cleaving the bond and relieving the steric strain of the 7-membered ring, allowing it to unroll.

Q: Is Nylon-6 an addition or condensation polymer?

It is generally classified as a condensation polymer because it contains amide linkages, similar to other condensation polymers. However, its specific synthesis mechanism is 'ring-opening polymerisation', where no small molecule byproduct (like water) is continuously eliminated during the chain growth.

Q: What gives Nylon-6 its high tensile strength?

The high tensile strength is due to strong intermolecular hydrogen bonding between the carbonyl oxygen (>C=O) of one chain and the amide hydrogen (-NH-) of an adjacent chain, which tightly binds the polymer fibers together.

Question

The structure of nylon-6 is

Options:

(A) $\left[ 	ext{-(CH}_2	ext{)}_6	ext{-C(=O)-NH-} ight]_n$

(B) $\left[ 	ext{-C(=O)-(CH}_2	ext{)}_5	ext{-NH-} ight]_n$

(C) $\left[ 	ext{-(CH}_2	ext{)}_4	ext{-C(=O)-NH-} ight]_n$

(D) $\left[ 	ext{-C(=O)(CH}_2	ext{)}_6	ext{-NH-} ight]_n$

Sigma Percentile · Accepted Answer

### The Ring-Opening Magic: Synthesizing Nylon-6

Polymers are the backbone of modern materials, and among them, polyamides hold a special place due to their incredible strength and durability. Today, we are diving into the structure and synthesis of one of the most famous polyamides: **Nylon-6**.

### Meeting the Monomer: Caprolactam

To understand the structure of Nylon-6, we must first look at its building block. Unlike Nylon-6,6 which is formed from two different monomers, Nylon-6 is synthesized from a single monomer called **Caprolactam**.

Caprolactam is a cyclic amide. If you look closely at its structure, it is a 7-membered ring. However, the name 'Nylon-6' comes from the number of carbon atoms it contains. The ring consists of:
- One carbonyl group: $	ext{-C(=O)-}$
- One amine group: $	ext{-NH-}$
- Exactly five methylene groups: $5 	imes 	ext{-CH}_2	ext{-}$

This gives us a total of 6 carbon atoms, hence the '6' in Nylon-6.

### The Polymerisation Process

How do we turn this closed ring into a long, continuous polymer chain? The answer lies in a process called **ring-opening polymerisation**.

When caprolactam is heated to a high temperature of about $533 	ext{ K}$ in an inert nitrogen atmosphere and in the presence of water, the ring becomes unstable. The weakest link in this cyclic structure is the amide bond—the bond directly connecting the carbonyl carbon to the nitrogen atom.

Under these conditions, this specific $	ext{C-N}$ bond breaks. Imagine taking a circular bracelet and snipping it at the clasp; it immediately unrolls into a straight line.

### Deriving the Repeating Unit

Once the ring opens, the molecule stretches out. Let's trace the unrolled chain from one end to the other:
1. It starts with the carbonyl group: $	ext{-C(=O)-}$
2. This is followed by the five methylene groups: $	ext{-(CH}_2	ext{)}_5	ext{-}$
3. It ends with the nitrogen atom: $	ext{-NH-}$

When thousands of these unrolled molecules link together head-to-tail, they form the polymer Nylon-6. Therefore, the repeating unit of the polymer is exactly:

$$\left[ 	ext{-C(=O)-(CH}_2	ext{)}_5	ext{-NH-} ight]_n$$

### Why is Nylon-6 so Strong?

Nylon-6 is renowned for its high tensile strength, elasticity, and resistance to abrasion. But where does this strength come from?

The secret lies in **hydrogen bonding**. The $	ext{-C(=O)-}$ group of one polymer chain forms strong intermolecular hydrogen bonds with the $	ext{-NH-}$ group of an adjacent chain. This creates a tightly packed, highly crystalline structure that makes Nylon-6 perfect for heavy-duty applications like tyre cords, ropes, and durable fabrics.

Animated Solution for Chemistry - Organic Chemistry: The structure of nylon-6 is

Select Answer:

Visualized Solution

\text{Monomer of Nylon-6}

\text{Structure of Caprolactam}

\text{Ring Opening Polymerisation}

\text{Breaking the Amide Bond}

\text{Repeating Unit of Nylon-6}

\text{Properties and Uses}

The Sigma Insight: Polymers

The Ring-Opening Magic

Meeting the Monomer

The Polymerisation Process

Deriving the Repeating Unit

Why is Nylon-6 so Strong?

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