MIDTERMs ORGCHEM -Lec 40-46

dienes

Alkenes that contain two carbon–carbon double bonds.

1,2-butadiene (CH₂=CH–CH=CH₂).

example of a diene.

It forms rubbery, elastic polymers.

What happens when butadiene polymerizes?

isoprene

A methyl derivative of butadiene that forms natural rubber structures

terpenes

Naturally occurring hydrocarbons made of isoprene units.

Cis-polyisoprene, a type of terpene.

What is natural rubber chemically?

Gutta percha

The trans form of polyisoprene, which is stiff and brittle.

material used for covering a golf ball

β-carotene

A terpene made of 8 isoprene units

vulcanization

The process of adding sulfur to rubber to strengthen it via cross-linking.

Charles Goodyear

Discovered that treating rubber with sulfur at varying temperature will make cross-linking of the polymers

Follow alkene rules, but replace “-ene” with “-diene”.

How are dienes named?

dehydration of alcohol

Removal of water to form an alkene (e.g., ethanol → ethene).

What reagents are used in dehydration?

Concentrated sulfuric acid (H₂SO₄) or alumina (Al₂O₃).

dehydrohalogenation

Removal of HX from a compound to form a double bond.

Colorless, faint sweet odor, lighter than air, slightly soluble in water.

What are the physical properties of ethene?

Addition of hydrogen to form ethane.

What is hydrogenation of ethene?

Addition of halogens to form dihaloethane.

What is halogenation of ethene?

Forms ethanol (hydration reaction)

What happens when ethene reacts with water?

mustard gas

A toxic compound formed from ethene and sulfur monochloride.

Produces CO₂ and H₂O with a sooty flame.

What happens during combustion of ethene?

• Production of polyethylene (plastic)

• Manufacture of alcohols

• Fruit ripening

• Used as anesthesia

What are uses of ethene?

alkynes

Unsaturated hydrocarbons with triple bonds.

CₙH₂ₙ₋₂

General formula of alkynes?

Ethyne (acetylene).

What is the first member of alkynes?

Use “-yne” suffix and number from the nearest triple bond.

How are alkynes named?

Reaction of calcium carbide + water.

How is ethyne prepared in the lab?

dehalogenation

Removal of halogens to form ethyne.

Physical properties of ethyne

Colorless gas, slightly soluble in water, burns with bright flame.

Due to impurities like H₂S or NH₃.

Why can ethyne smell like garlic?

Forms ethene, then ethane.

What happens in hydrogenation of ethyne?

hydration of ethyne

Addition of water to form alcohols

halogenation of ethyne

Forms tetrahalides

uses of ethyne

• Welding (oxy-acetylene flame)

• Artificial fruit ripening

• Production of plastics and chemicals

acetylenic linkage

The carbon–carbon triple bond (C≡C) found in alkynes.

Edmond Davy

Who discovered ethyne (acetylene)?

Oxalic acid is formed.

What is formed when ethyne reacts with alkaline potassium permanganate (KMnO₄)?