Aliphatic hydrocarbons are open‐chain compounds that may be saturated or unsaturated. The saturated compounds, known as
paraffin hydrocarbons
or
alkanes
, include methane and its homologs having the empirical formula C
n
H
2
n
+2
. The unsaturated compounds fall into a number of homologous series: (
1
) those containing one double bond (ethylene and its homologs) and having the formula C
n
H
2
n
are known as
olefins
or
alkenes
; (
2
) those containing one triple bond (acetylene and its homologs) are called
acetylenes
or
alkynes
and have the formula C
n
H
2
n
−2
; (
3
) those having two double bonds (allene, 1,3‐butadiene and 1,4‐pentadiene represent three types) are
diolefins
or
alkadienes
and also have the formula C
n
H
2
n
−2
; (
4
) those having a large number of double or triple bonds or both double and triple bonds are named in analogous fashion as
alkatrienes
,
alkatetraenes
,
alkadiynes
,
alkenynes
, and
alkadienynes
.
Aliphatic hydrocarbons are asphyxiants and
central nervous system
(
CNS
) depressants. Serious toxic effects of aliphatic hydrocarbons include asphyxia and chemical pneumonitis for many paraffins, axonal neuropathy for
n
‐hexane, and cancer for 1,3‐butadiene.