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, formally bicyclo .2.1eptane. , a heterocyclic, bridged bicyclic compound, formally named 1,4-diazabicyclo .2.2ctane. A bicyclic molecule (''bi'' = two, ''cycle'' = ring) is a molecule that features two joined Cyclic compound, rings. Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and
camphor Camphor () is a waxy, flammable , Germany Image:Tu braunschweig 750 grad ofen.jpg, 250px, Germany, German test apparatus for determining combustibility at Technische Universität Braunschweig A combustible material is something that can co ...
. A bicyclic compound can be carbocyclic (all of the ring atoms are carbons), or
heterocyclic 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemistry is the branch of organi ...
(the rings atoms consist of at least two elements), like
DABCO
DABCO
. Moreover, the two rings can both be aliphatic (''e.g.''
decalin Decalin (decahydronaphthalene, also known as bicyclo .4.0ecane and sometimes decaline), a bicyclic organic compound, is an industrial solvent. A colorless liquid with an aromatic odor, it is used as a solvent for many resins or fuel additives. It ...
and norbornane), or can be aromatic (''e.g.''
naphthalene Naphthalene is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ca ...

naphthalene
), or a combination of aliphatic and aromatic (''e.g.''
tetralin Tetralin (1,2,3,4-tetrahydronaphthalene) is a hydrocarbon In organic chemistry, a hydrocarbon is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that conta ...
). Three modes of ring junction are possible for a bicyclic compound: * In spirocyclic compounds, the two rings share only one single atom, the spiro atom, which is usually a quaternary carbon. An example of a spirocyclic compound is the photochromic switch spiropyran. * In fused bicyclic compounds, two rings share two adjacent atoms. In other words, the rings share one covalent bond, ''i.e.'' the so-called bridgehead atoms are directly connected (''e.g.'' α-thujene and
decalin Decalin (decahydronaphthalene, also known as bicyclo .4.0ecane and sometimes decaline), a bicyclic organic compound, is an industrial solvent. A colorless liquid with an aromatic odor, it is used as a solvent for many resins or fuel additives. It ...
). * 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 .2.1eptane, can be viewed as a pair of cyclopentane rings each sharing three of their five carbon atoms. Camphor is a more elaborate example. Image:Bicycloalkanes1.svg, 300 px, left, C8, C9, and C11 bicyclic alkanes. The bridgehead atoms are the carbons from which ''three'' bonds radiate, like spokes:bicyclo .2.2ctane, bicyclo-[3.3.1]nonane, bicyclo[3.3.3]undecane.


Nomenclature

Bicyclic molecules are described by IUPAC nomenclature of organic chemistry, IUPAC nomenclature. The root of the compound name depends on the total number of atoms in all rings together, possibly followed by a suffix denoting the functional group with the Cahn–Ingold–Prelog priority rules, highest priority. Numbering of the carbon chain always begins at one bridgehead atom (where the rings meet) and follows the carbon chain along the longest path, to the next bridgehead atom. Then numbering is continued along the second longest path and so on. Fused and bridged compounds, bridged bicyclic compounds get the prefix ''bicyclo'', whereas spiro compounds, spirocyclic compounds get the prefix ''spiro''. In between the prefix and the suffix, a pair of brackets with numerals denotes the number of carbon atoms between each of the bridgehead atoms. These numbers are arranged in descending order and are separated by periods. For example, the carbon frame of norbornane contains a total of 7 atoms, hence the root name heptane. This molecule has two paths of 2 carbon atoms and a third path of 1 carbon atom between the two bridgehead carbons, so the brackets are filled in descending order: [2.2.1]. Addition of the prefix ''bicyclo'' gives the total name bicyclo .2.1eptane. The carbon frame of
camphor Camphor () is a waxy, flammable , Germany Image:Tu braunschweig 750 grad ofen.jpg, 250px, Germany, German test apparatus for determining combustibility at Technische Universität Braunschweig A combustible material is something that can co ...
also counts 7 atoms, but is substituted with a Carbonyl group, carbonyl in this case, hence the suffix heptanone. We start with numbering the carbon frame at the bridgehead atom with the Cahn–Ingold–Prelog priority rules, highest priority (Methyl group, methyl goes before Hydrogen atom, proton), hence the bridgehead carbon in front gets number 1, the carbonyl gets number 2 and numbering continues along the carbon chain following the longest path, until the doubly substituted top carbon (number 7). Equal to norbornane, this molecule also has two paths of 2 carbon atoms and one path of 1 carbon atom between the two bridgehead carbons, so the numbers within the brackets stay [2.2.1]. Combining the brackets and suffix (now filling in the position of the carbonyl as well) gives us .2.1eptan-2-one. Besides ''bicyclo'', the prefix should also specify the positions of all Methyl group, methyl substituents so the complete, official name becomes 1,7,7-trimethylbicyclo .2.1eptan-2-one. When naming simple fused bicyclic compounds, the same method as for bridged bicyclic compounds is applied, except the third path between the two bridgehead atoms now consists of zero atoms. Therefore, fused bicyclic compounds have a "0" included in the brackets. For example,
decalin Decalin (decahydronaphthalene, also known as bicyclo .4.0ecane and sometimes decaline), a bicyclic organic compound, is an industrial solvent. A colorless liquid with an aromatic odor, it is used as a solvent for many resins or fuel additives. It ...
is named bicyclo .4.0ecane. The numbers are sometimes omitted in unambiguous cases. For example, bicyclo[1.1.0]butane is typically called simply bicyclobutane. The
heterocyclic 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemistry is the branch of organi ...
molecule
DABCO
DABCO
has a total of 8 atoms in its bridged structure, hence the root name octane. Here the two bridgehead atoms are nitrogen atom, nitrogen instead of carbon atoms. Therefore, the official name gets the additional prefix ''1,4-diaza'' and the total name becomes 1,4-diazabicyclo .2.2ctane.


References


See also

*Polycyclic compound *Bredt's rule {{Authority control Molecular geometry Bicyclic compounds, *