Alkynes GroupAlkynes is hydrocarbons which respectively have carbon-carbon triple bond functional groups.NAMING ALKYNESAlkynes end in the suffix -yne, and are numbered in the same manner as alkenes, with the first carbon of the alkyne being numbered to specify its position. The triple bond is given the lowest number possible. Compounds containing double and triple bonds are named with the suffix -enyne. In this case the numbering begins at the side of the chain that is closer the multiple bond. If there is a choice the double bond gets priority. Of course there is no cis or trans Z or E in alkynes.

Example:

Penta-1,3-diyne

Hexa-1,5-dien-3-yne

Hex-1-ene-3,5-diyne

You must relate where each multiple bond is on the carbon chain. Simply insert the position number in front of the appropriate suffix.

Example

3-penten-1-yne

Longest chain? 5, therefore pentCarbon alkyne starts on? In this case, the end carbon of the triple bond gets a 1 because it is closer to the

end of the longest chain than the double bondCarbon alkene starts on? 3

Nomenclature• IUPAC: use the infix -yneyne- to show the

presence of a carbon-carbon triple bond.

• Common names: prefix the substituents on the triple bond to the word “acetylene”.

Common name:IUPAC name:

DimethylacetyleneVinylacetylene2-Butyne 1-Buten-3-yne

1

1,6-Heptadiyne3-Methyl-1-butyne 6,6-Dimethyl-3-heptyne

23

4

1

2 3 4

5

6 12

34

56

7 7

SOME EXAMPLES:

1-octen-5-yne

The double bond is nearest to the end of the longest chain, so it receives numbering priority.

5-ethyl-3-heptyne

Just like alkenes, the position of the triple bond goes before the name of the parent chain

Try to give name of the compounds bellow:

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Properties of Alkynes* Physical stateThe first three members (ethyne, propyne and butyne) are colourless and odorless gases. Due to the presence of phosphine as an impurity ethyne (acetylene) has garlic smell. The next eight members are liquids, and higher members are solids under normal conditions of temperature and pressure.

* SolubilityAlkynes are insoluble in water, but are fairly soluble in organic solvents such as, alcohol, ether, acetone etc.

* Melting PointsThe melting and boiling points of alkynes increase with molecular mass.

Uses of Alkynes

Alkynes are generally used as the starting materials for the

manufacture of a large number of organic compounds of industrial importance such as, chloroprene,

vinyl chloride etc.

Isomerism in Alkynes

Positional IsomerismIt is due to the different arrangement of carbon atoms in the chain i.e., straight chain or a branched-chain e.g.,

It is due to the difference in the location of the triple bond, i.e.,

PolymersPolymers: A large molecule formed by the repetitive bonding together of many smaller molecules called monomers. Many simple alkenes undergo polymerization reaction when treated with the proper catalyst.

a). Addition PolymerisationThis kind of polymerisation is typified by the presence of a carbon – carbon double bond in the monomer.

Example: Polypropylene

In addition polymerisation:• The polymer is the only product• Involves the opening out of a double bond• The conditions of the reaction can alter the properties of the polymer

Another example:

b. Condensation polymersA condensation polymer generally involves 2 monomers that have different functional groups.They also involve the elimination of water or another small molecule. Hence the term condensation polymer.

Monomer A + Monomer B Polymer + small molecule (normally water).

Common condensation polymers include polyesters (the ester linkage) and polyamides (the amide linkage as in proteins).

Example: The example here is terylene, a polymer of benzene-1,4-dicarboxylic acid and ethane-1,2-diol. The ester linkage is based around the reaction between an acid and an alcohol to form an ester + water.

EXERCISESPredicting the repeating unit.

Predicting the monomer from the polymer