Alkanes, especially straight-chain or n-alkanes, are the major constituents of petroleum. Since
different alkanes, not to mention their respective isomers, have different boiling and melting points,
the different alkane components in petroleum can be separated by distillation. Those compounds
with the lowest boiling points would vaporize first; one can trap these vapors and condense them
and thus achieve a separation of the more volatile from the less volatile components.
ALKENES
Alkenes are hydrocarbons involving carbon-carbon double bonds. They possess a molecular formula
of the form CnH 2 n. They are named using the same scheme as alkanes, except that the suffix used is -
ene. Also, since it takes at least two carbon atoms to form a double bond, the smallest alkene is
ethene, C 2 H 4 , which contains two carbon atoms.
ALKYNES
Alkynes are hydrocarbons involving carbon-carbon triple bonds. They follow the same naming
scheme as alkanes and alkenes, but use the suffix -yne. Alkenes and alkynes are said to be
unsaturated, while alkanes are said to be saturated.
CYCLIC COMPOUNDS
We have only considered noncyclic compounds so far. Alkanes, alkenes, or alkynes can also be
cyclic: The carbon atoms form a ring. Such compounds are named exactly as they would normally
be, but with the additional prefix cyclo- attached at the beginning. The smallest number of carbon
atoms that is needed to form a ring is three; the smallest cyclic alkane is therefore cyclopropane.
The structures of cyclohexane, cyclohexene, and cyclohexyne are shown on the next page.