Alkynes Group

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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.
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Example
Penta-1,3-diyne
Hexa-1,5-dien-3-yne
Hex-1-ene-3,5-diyne
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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
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Nomenclature

• IUPAC use the infix -yne- to show the presence
  of a carbon-carbon triple bond.
• Common names prefix the substituents on the
  triple bond to the word acetylene.

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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
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Try to give name of the compounds bellow
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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.
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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.
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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.,
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It is due to the difference in the location of
the triple bond, i.e.,
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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
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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
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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).
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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.
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EXERCISES
Predicting the repeating unit.
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Predicting the monomer from the polymer