In
chemistry, an
open-chain compound (also spelled as open chain compound) or
acyclic compound (Greek prefix "α",
without and "κύκλος",
cycle) is a compound with a linear structure, rather than a
cyclic one. An open-chain compound having no
side chains is called a
straight-chain compound (also spelled as straight chain compound). Many of the simple molecules of
organic chemistry, such as the
alkanes and
alkenes, have both linear and ring
isomers, that is, both acyclic and
cyclic, with the latter often classified as
aromatic. For those with 4 or more carbons, the linear forms can have straight-chain or branched-chain isomers. The lowercase prefix
n- denotes the straight-chain isomer; for example,
n-butane is straight-chain
butane, whereas
i-butane is
isobutane.
Cycloalkanes are isomers of
alkenes, not of
alkanes, because the ring's closure involves a C=C bond.