| Cycloalkanes |
| Whilst many of
the alkanes present in crude oil are aliphatic,
having straight–or branched–chain molecules,
some of them form rings – they are alicyclic.
These compounds are denoted as cycloalkanes.
These cycloalkanes have the
general formula CnH2n
instead of CnH2n+2
for the chain molecules. Cycloalkanes behave
very similarly to the other alkanes, but they
tend to have higher melting and boiling points.
They have the same name as the corresponding
straight–chain molecule, but with the prefix
'cyclo–'. These ring molecules are not
aromatic compounds – the aromatic ring
structure is based on the benzene ring. |
| Because of the
restricted movement available to a cyclic compound,
it undergoes a number of different types of
strain. The smallest cycloalkane is cyclopropane,
which forms a triangular molecule which is much
more reactive than straight–chain propane. Cyclobutane
forms a square molecule, which is less reactive
than cyclopropane, but is more reactive than
butane. Cyclopentane and higher cycloalkanes
have a similar reactivity to their straight–chain
equivalents. The structures of these cycloalkanes
are shown below. A shortcut notation is used
to represent the structure where only the bonds
are shown and intersection of bonds represents
carbon atoms. Because of the tremendous angle
strain cyclopropane is very reactive. |
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