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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.

Table of Content

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.

Cycloaddition:

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

Addition of Water:

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.

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