copmounds have the same empirical formulae, ie all of the same atoms however they are arranged
differently. There are various sorts of isomer such as, optical isomers where two isomers are formed
which are mirror images and they are non-superimposable and linkage isomerism, where the way the
molecules are attached differs for example NO2 and ONO. The different ways in which
the atoms and molecules are arranged gives the isomers slightly different properties. Isoprene
shows geometrical isomerism
When in the trans-1,4-polyisoprene form all of the CH3 groups are all along the same
side giving an ordered (crystalline) structure leading to this isomer being hard abd rigid.
On the other hand in the cis form, (cis-1,4-polyisoprene) the CH3 groups are
on alternating sides which gives an amorphous structure and elastic and soft properties.
The way these isomers are put together also affects their properties, when isoprene is
polymerised it can lead to three arrangements. The first is Isotactic, this is when all
of the side groups are on the same side of the molecule, this gives a very crystalline
structure and therefore a very high boiling point. Syndiotactic is when the side groups are
on alternating sides giving a lower boiling point and a more amorphous structure. The last
is called Atactic and the side groups are randomly arranged leading to an even more amorphous
structure and the lowest boiling point.
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