al·i·phat·ic 
(ăl′ə-fătĭk)
(ăl′ə-fătĭk)adj.
Of, relating to, or designating a group of organic chemical compounds in which the carbon atoms are linked in open chains.
[From Greek aleiphar, aleiphat-, oil, from aleiphein, to anoint with oil; see leip- in the Appendix of Indo-European roots.]
aliphaticstraight chain of carbon atoms of a propane molecule