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# Diene

## What is Dienes?

Diene is an unsaturated compound containing two double bonds between carbon atoms. Diene is used in industries as a monomer subunit of complex polymer. It is also used in Organic Synthesis.

This section will discuss the nomenclature, classes, synthesis, physical properties, chemical properties and applications of dienes.

## Nomenclature of Diene

• IUPAC names Dienes in the same way as alkenes are named.
• In the end, we use diene as a suffix.
• In the beginning, we use two numbers to specify the position of two double bonds.

Example

## Classes of Diene

Based on the relative position of the double bond in the overall molecule, Dienes are classified into three classes:

• Cumulated Diene: A cumulated diene has two successive double bonds on adjacent Carbon. They are also called Allene.
• Conjugated Diene: A conjugated diene has two conjugated double bonds separated by a single bond.
• Isolated Diene: An isolated diene has two double bonds separated by two or more double bonds.

## Synthesis of Dienes

### Dehydrohalogenation of Dihalides

Dienes can be prepared by Dehydrohalogenation of dihalides by successive elimination reactions.

XCH2CH2CH2CH2X

$$\begin{array}{l}\xrightarrow[KOH]{alcohol}\end{array}$$
H2CCHCHCH2

### Dehydration of Diols

Dienes can be prepared by dehydration of diols by two successive elimination reactions.

OHCH2CH2CH2CH2OH

$$\begin{array}{l}\overset{H^+}{\rightarrow}\end{array}$$
H2CCHCHCH2

### Other Methods of Preparation of Dienes

• Butadiene is prepared in industries by thermal cracking of Butane.
• Dicyclopentadiene is prepared in industries from Coal tar.

## Physical Properties of Diene

### Nature:

In diene, the position adjacent to a double bond is acidic. Diene’s acidic character is due to the extra stability of allyl ion due to resonance.

### Stability:

• Conjugated dienes are more stable than non-conjugated dienes because of the delocalisation of electron clouds on Carbon atoms.
• E.g. In conjugated 1,3 Butadiene, all four pi electrons are delocalised over all four Carbon atoms.
• The delocalisation of pi electrons makes the compound more stable.

## Chemical Properties of Diene

### Polymerisation:

Diene polymerises to form rubber.

• 1,3 Butadiene polymerises to form buna rubber used in tyres.
• Isoprene polymerises to form natural rubber.

Diel- Alder Reaction is an essential reaction shown by diene. A conjugated diene reacts with substituted alkene (dienophile) to form a substituted cyclohexene derivative.

When we add water to diene in a catalytic amount of strong acid, corresponding enol is formed.

.

CH2=CHCH=CH2 →CH3CH(OH)CH=CH(But-1-en-2-ol) + CH3CH=CHCH2OH (But-2-en-1-ol)

## Applications of Diene

• Dienes are widely used in industries as monomer subunits of complex polymers.
• 1,3 Butadiene polymerises to form buna rubber used in tyres.
• Isoprene polymerises to form natural rubber.
• Dienes are used in organic synthesis.
• Dienes are used as chelating ligands in Organometallic Chemistry.

## Frequently Asked Questions on Diene

### What is a diene?

Dienes are unsaturated compounds containing two double bonds in between carbon atoms.

### What are the different classes of dienes?

Based on the relative position of the double bond in the overall molecule, Dienes are classified into three classes:

• Cumulated Diene: A cumulated diene has two successive double bonds on adjacent Carbon. They are also called Allene.
• Conjugated Diene: A conjugated diene has two conjugated double bonds separated by a single bond.
• Isolated Diene: An isolated diene has two double bonds separated by two or more double bonds.

### What is the diel alder reaction?

Diel Alder Reaction is a reaction between a substituted alkene and a conjugated diene to form a substituted cyclohexene derivative.

• It is a type of pericyclic reaction.

### Why are conjugated dienes more stable?

• Conjugated Dienes are more stable than non-conjugated dienes because of the delocalisation of electron clouds on Carbon atoms.
• E.g. In conjugated 1,3 Butadiene, all four pi electrons are delocalised over all four Carbon atoms.
• The delocalisation of pi electrons makes the compound more stable.

### What are the applications of dienes?

• Dienes are widely used in industries as monomer subunits of complex polymers.
• 1,3 Butadiene polymerises to form buna rubber used in tyres.
• Isoprene polymerises to form natural rubber.
• Dienes are also used in organic synthesis.