Bicyclic molecule
Molecule with two joined rings / From Wikipedia, the free encyclopedia
A bicyclic molecule (from bi 'two' and cycle 'ring') is a molecule that features two joined rings.[1] Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and camphor. A bicyclic compound can be carbocyclic (all of the ring atoms are carbons), or heterocyclic (the rings' atoms consist of at least two elements), like DABCO.[2] Moreover, the two rings can both be aliphatic (e.g. decalin and norbornane), or can be aromatic (e.g. naphthalene), or a combination of aliphatic and aromatic (e.g. tetralin).
Three modes of ring junction are possible for a bicyclic compound:[3]
- In spiro compounds, the two rings share only one single atom, the spiro atom, which is usually a quaternary carbon.[4] An example of a spirocyclic compound is the photochromic switch spiropyran.
- In fused/condensed[5] bicyclic compounds, two rings share two adjacent atoms. In other words, the rings share one covalent bond, i.e. the bridgehead atoms are directly connected (e.g. α-thujene and decalin).
- In bridged bicyclic compounds, the two rings share three or more atoms, separating the two bridgehead atoms by a bridge containing at least one atom. For example, norbornane, also known as bicyclo[2.2.1]heptane, can be viewed as a pair of cyclopentane rings each sharing three of their five carbon atoms. Camphor is a more elaborate example.