The homopolymer formed from 4-hydroxybutanoic acid is
(a) [-O-C(=O)-(CH2)3-O-]n
(b) [-O-C(=O)-(CH2)2

Q: Why does the acid lose OH and the alcohol lose H during esterification?

In the mechanism of esterification, the oxygen of the alcohol acts as a nucleophile and attacks the carbonyl carbon of the acid. The acid's -OH group is eventually protonated and leaves as a water molecule.

Q: Can this monomer form a cyclic ester instead of a polymer?

Yes, 4-hydroxybutanoic acid can undergo intramolecular esterification to form a 5-membered cyclic ester called gamma-butyrolactone. However, under polymerization conditions (like heating), it forms the linear polyester.

Q: Why is it called a homopolymer if water is eliminated?

A homopolymer is defined by being synthesized from a single type of monomer unit. Even though water is eliminated (making it a condensation polymer), there is only one starting monomer, so it is still a homopolymer.

Q: How do I know which end of the repeating unit to draw first?

It doesn't matter! The repeating unit `[-O-(CH2)3-C(=O)-]` is exactly the same as `[-C(=O)-(CH2)3-O-]`. They both represent the same continuous chain.

Q: Is this polymer biodegradable?

Yes! Aliphatic polyesters like poly(4-hydroxybutyrate) are generally biodegradable because the ester linkages can be broken down by enzymes and water in the environment.

Question

The homopolymer formed from 4-hydroxybutanoic acid is

Sigma Percentile · Accepted Answer

### The Monomer's Anatomy

Let's dive into the fascinating world of polymers! Our starting material today is **4-hydroxybutanoic acid**.

If we look closely at its structure, we notice something special. It is a bifunctional molecule, meaning it has two different reactive groups on the same chain.

On one end, we have a hydroxyl group ($-OH$), and on the other end, a carboxylic acid group ($-COOH$).

$$HO-CH_2-CH_2-CH_2-COOH$$

This dual nature is the perfect recipe for a specific type of reaction. When a molecule has both an alcohol and an acid group, it is primed for **condensation polymerization**.

### The Condensation Dance

Imagine millions of these monomer units floating around. When they come close to each other, a chemical dance begins.

The carboxylic acid group of one molecule approaches the hydroxyl group of its neighbor.

To link up, they must sacrifice something. The acid group gives up its $-OH$, and the alcohol group gives up its $-H$.

Together, these form a water molecule ($H_2O$), which is eliminated from the system.

$$-	ext{COOH} + 	ext{HO}- ightarrow -	ext{COO}- + H_2O$$

This elimination process is why we call it a condensation reaction. The newly formed bond is an **ester linkage**, tightly binding the two monomer units together.

### Building the Chain

As this process repeats over and over, a long chain begins to form.

Every time a new monomer joins, another water molecule is lost. The resulting long-chain molecule is a polyester.

To find the repeating unit of this polymer, we simply take the original monomer and remove the $-H$ from the alcohol end and the $-OH$ from the acid end.

What we are left with is the core repeating structure:

$$\left[ -O-(CH_2)_3-C(=O)- ight]_n$$

### Connecting to the Options

Now, let's look at our options. We need to find the structure that perfectly matches our derived repeating unit.

Option (c) shows exactly this structure: an oxygen atom, followed by three methylene groups, and ending with a carbonyl group.

Therefore, the correct homopolymer is represented by option (c).

As a bonus fact, aliphatic polyesters like this one are often **biodegradable**. This makes them incredibly important for environmentally friendly materials!

Animated Solution for Chemistry - Organic Chemistry: The homopolymer formed from 4-hydroxybutanoic acid is

Select Answer:

Visualized Solution

$4 -hydroxybutanoic acid$

$Condensation Polymerization$

$Reaction Setup$

$Elimination of Water$

$Repeating Unit$

$Key Takeaway$

The Sigma Insight: Polymers

The Monomer's Anatomy

The Condensation Dance

Building the Chain

Connecting to the Options

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