Hydrocarbons Fossil Fuels Hydrocarbons compounds  Elmhurst College
Alkanes or Chime Alkynes or Chime  Rings or Chime  Chemistry Department
Alkenes or Chime Aromatic or Chime Boiling Points  Virtual ChemBook

 Ethene or Ethylene 

  model (spacefill / ball & stick)

Color Codes

C

 H

 N

 O

 P

 S

 Cl

 F

 1-Pentene 

  model (spacefill / ball & stick)

Color Codes

C

 H

 N

 O

 P

 S

 Cl

 F
 

 ALKENES

 Alkenes area class of HYDROCARBONS which contain only carbon and hydrogen. Two other terms which describe alkenes are unsaturated and olefins.

UNSATURATED hydrocarbons contain either double or triple bonds. Since the compound is unsaturated with respect to hydrogen atoms, the extra electrons are shared between 2 carbon atoms forming double bonds in alkenes.

Alkenes are also called OLEFINS because they form oily liquids on reaction with chlorine gas.

The example compounds of ethene or ethylene and pentene are shown on the LEFT.

Ethylene is the number one organic chemical synthesized in the U. S. and the world. The small quantities of ethane, propane, and butane found in natural gas are converted into ethene. It can be produced by thermal cracking of ethane to produce ethene and a hydrogen molecule.

Alkenes are the raw materials for a number of plastics such as polyethylene, PVC, polypropylene, and polystyrene.

Alkene chemistry is found in unsaturated fats, beta-carotene, and seeing light through vision.

Properties

 Structure

 Physical Properties

 Chemical Reactivity

 CnH2n

Example: CH2CH2

Boiling points depend on chain length, slightly less than alkanes.

Non polar

Insoluble in water

Less dense than water

Alkenes are quite reactive because of the presence of the double bond. Many small compounds react by addition i.e. molecules add to the alkene to form one product.

All compounds: Combustion Reaction

ALKENE NAMES
Root names give the number of carbons in the longest continuous chain. Alkene names are formed by dropping the "ane" and replacing it with "ene"

The following list gives samples:

Example: root = propane - drop "ane" = "prop"
alkene = "prop" + alkene ending = "ene" = propene

 No. of
Carbons

 Root Name

 Formula
CnH2n

 Structure

 2

 ethene
 C2H4  CH2=CH2

 3

 propene
 C3H6  CH2=CHCH3

 4

1-butene
 C4H8  CH2=CHCH2CH3

 5

 1-pentene
  C5H10  CH2=CHCH2CH2CH3