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

 
 
 

 ALKYNES - Acetylene

 Alkynes area class of HYDROCARBONS which contain only carbon and hydrogen. Two other terms which describe alkynes are unsaturated and acetylenes.

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

Alkynes are also generally known as ACETYLENES from the first compound in the series.

The example compound of ethyne or acetylene is shown on the LEFT.

Acetylene can be produced from the reaction of solid calcium carbide and water.
CaC2 + 2 H2O ---> C2H2 + Ca(OH)2

A Carbide Lamp is a two part container usually made of brass for generating acetylene gas. Water which drips from the top part onto the solid calcium carbide in the bottom part generates acetylene gas that escapes through a tiny hole in a tip or nozzle directed horizontally from the front of the container. The gas is then ignited by sparks from a steel wheel spun over flint, mounted on a reflector 2.5 inches in diameter. The lamp is mounted on the front of a hard hat, so that light is directed in whichever direction the wearer turns his head. Miners and cave explorers used to use them.

Acetylene burns in air with a yellow sooty flame and also produces carbon monoxide (incomplete combustion). However, if acetylene is mixed with an excess of oxygen, it burns with a very hot blue flame (as high as 3000oC). This very exothermic reaction is the basis of oxyacetylene torches used in welding and cutting metals.

Properties

 Structure

 Physical Properties

 Chemical Reactivity

 CnH2n-2

Example: CH=CH

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

Non polar

Insoluble in water

gas at room temperature

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

All compounds: Combustion Reaction

ALKYNE NAMES
Root names give the number of carbons in the longest continuous chain. Alkyne names are formed by dropping the "ane" and replacing it with "yne"

The following list gives samples:

Example: root = ethane - drop "ane" = "eth"
alkene = "eth" + alkyne ending = "yne" = ethyne

 No. of
Carbons

 Root Name

 Formula
CnH2n-2

 Structure

 2

 ethene
 C2H2  CH=CH

 3

 propene
 C3H4  CH=CHCH3

 4

1-butene
 C4H6  CH=CCH2CH3

 5

 1-pentene
  C5H8  CH=CCH2CH2CH3