Open-chain compound
In chemistry, an open-chain compound (or 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.[1] An open-chain compound having no
side groups is called a straight-chain compound (also spelled as straight chain compound).[2][3] 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. 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. Having no rings (aromatic or otherwise), all open-chain compounds are aliphatic
.
Typically in biochemistry, some isomers are more prevalent than others. For example, in living organisms, the open-chain isomer of glucose usually exists only transiently, in small amounts; D-glucose is the usual isomer; and L-glucose is rare.
Straight-chain molecules are often not literally straight, in the sense that their
bond angles are often not 180°, but the name reflects that they are schematically
straight. For example, the straight-chain alkanes are wavy or "puckered", as the models below show.
|
|
|
| branched-chain | straight-chain | cyclic |
| open-chain | ||
References
- PMID 5645558.