Bridged compounds

3D ball-and-stick representation of the bridged bicyclic compound, norbornane. Formally bicyclo[2.2.1] heptane. This representation shows all atoms, and makes clear its non-planar nature.
Line-angle representation of norbornane. Here, every vertex indicates a carbon atom, with the carbon valence of 4 is filled up by hydrogen atoms not shown. The bridge is one atom, the topmost vertex shown. Two bridgehead atoms are indicated by blue arrows.

A bridged compound is a chemical compound, generally an organic compound, but also possibly inorganic, that has two or more rings (a ring system) that contains a bridge—a single atom or an unbranched chain of atoms (or even just a valence bond) that connect two "bridgehead" atoms. The bridgehead atoms are defined as any atom that is not a hydrogen, and that is part of the skeletal framework of the molecule that is bonded to three or more other skeletal atoms.[1]:VB-1 Clayden simplifies this description, saying that bridged bicyclic compounds "are just what the name implies—[molecules in which] a bridge of [an atom or of atoms] is thrown across from one side of the ring to the other,"[2]:839 examples of which are shown at left and right, and below. The presence of the bridge connecting the bridgehead atoms, which are most often two non-adjacent atoms, distinguishes bridged compounds from fused ring compounds that have two rings linked by two adjacent atoms, and from spiro compounds that have two rings linked by a single atom.[2]:653ff :839ff

Bridged compounds may be fully carbocyclic (all carbon) or heterocyclic (having one or more non-carbon atoms). The principle and bridging rings are almost always different in nature, though they can be identical. Although sketches of organic structures may make bridged compounds appear planar, they are not; for instance, comparing the 3D ball-and-stick model of norbornane at left, with the image shown at right, makes clear the bridging ring ensures that the molecule is not planar.

Nomenclature

C8, C9, and C11 bridged bicyclic alkanes. The bridgehead atoms are the carbons from which three bonds radiate above and below from it, like spokes; there are two in each example, one to the front and the other to the rear of the molecule as presented to the viewer. At left is bicyclo[2.2.2]octane; count and compare the total carbons (vertices) to the root name octane; compare the bracketed numbers to the number of carbons in each bridge connecting the bridgehead carbons. The center molecule is bicyclo-[3.3.1]nonane. At right is bicyclo[3.3.3]undecane.

The nomenclature of bridged compounds was established by the IUPAC based on the system introduced by von Baeyer.[3] Some important concepts and definitions for bridged compounds are as follows.

Examples

Examples include: norbornane, shown above, along with other alicyclic (purely hydrocarbon) examples in the Nomenclature section; adamantane and its amine analogs memantine (shown), amantadine (shown), and rimantadine (the latter two historic influenza drugs); the heteroatom bridgehead examples hexamine (shown) and 1,4- Diazabicyclo[2.2.2]octane (DABCO, shown in two representations); morphan, an example having a heteroatom in a bridge (shown); biperiden; and methenamine.

Chemical diagram
amantadine
Chemical diagram
memantine
Chemical diagram
hexamine
Chemical diagram
morphan
Chemical diagram
DABCO
Chemical diagram
DABCO, alternative representation of bicyclic rings

Further reading

The following are texts and other sources covering the title subject.

Secondary sources

Primary sources

Notes and references

  1. 1 2 3 4 5 6 Moss, G.P. and the Working Party of the International Union of Pure and Applied Chemistry [IUPAC], Organic Chemistry Division, Commission on Nomenclature of Organic Chemistry (III.1) (1999). "Extension and Revision of the von Baeyer System for Naming Polycyclic Compounds (Including Bicyclic Compounds); (IUPAC Recommendations 1999)" (PDF). Pure Appl. Chem. 71 (3): 513–529. doi:10.1351/pac199971030513. ISSN 1365-3075. Retrieved 3 February 2016. Note, the article co-authors, the Working Party of the IUPAC (1992-1998), were P. M. Giles, Jr., E. W. Godly, K.-H. Hellwich, A. K. Ikizler, M. V. Kisakürek, A. D. McNaught, G. P. Moss, J. Nyitrai, W. H. Powell, O. Weissbach, and A. Yerin. Also available online at "Extension and Revision… [as above]". London, GBR: Queen Mary University of London. Retrieved 3 February 2016. Also available in German, with et al. indicating the same working party, at Hellwich, Karl-Heinz et al. (2002). "Erweiterung und Revision des von-Baeyer-Systems zur Benennung polycyclischer Verbindungen (einschließlich bicyclischer Verbindungen)". Angewandte Chemie. 114 (17, September 2): 3423–3432. doi:10.1002/1521-3757(20020902)114:17<3423::AID-ANGE3423>3.0.CO;2-6. Retrieved 3 February 2016. Die Übersetzung basiert auf der „Extension and Revision of the von Baeyer System for Naming Polycyclic Compounds (Including Bicyclic Compounds)“ der Commission on Nomenclature of Organic Chemistry (III.1) der Organic Chemistry Division der International Union of Pure and Applied Chemistry, veröffentlicht in Pure Appl. Chem.1999, 71, 513–529.
  2. 1 2 Clayden, Jonathan ; Greeves, Nick & Warren, Stuart (2012). Organic Chemistry (2nd ed.). Oxford, UK: Oxford University Press. pp. 432ff, 653ff, 839ff, and passim. ISBN 0199270295. Retrieved 2 February 2016.
  3. ↑ "Von-Baeyer-System". chemie.de. Retrieved 2 March 2016.

See also

External links

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