Alkynes Group
Alkynes is hydrocarbons which respectively have
carbon-carbon triple bond functional groups.
NAMING ALKYNES
Alkynes 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 pent
Carbon 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 bond
Carbon alkene starts on? 3
Nomenclature
• IUPAC: use the infix -yne- to show the
presence of a carbon-carbon triple bond.
4
3
2
1
2
3
4
6
7
5
1
2
3
4
6
7
5
1
3-Methyl-1-bu tyn e
6,6-D imethyl-3-hep tyn e
1,6-Hep tadiyne
• Common names: prefix the substituents on
the triple bond to the word “acetylene”.
IUPAC n ame :
2-Bu tyn e
1-Bu te n -3-yn e
C omm on n ame : D i me th ylace tyl en e Vi nyl ace tyl e n e
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:
_________________________
_________________________
_________________________
_________________________
_________________________
Properties of Alkynes
* Physical state
The 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.
* Solubility
Alkynes are insoluble in water, but are fairly soluble in
organic solvents such as, alcohol, ether, acetone etc.
* Melting Points
The 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 Isomerism
It 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.,
Polymers
Polymers: 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 Polymerisation
This 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 polymers
A 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-1,4dicarboxylic 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.
EXERCISES
Predicting the repeating unit.
Predicting the monomer from the polymer