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ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module 7: Annulenes Know More Weblinks https://en.wikipedia.org/wiki/Annulene http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/12/oc/vlu_organik/aromaten/aro maten/weitere_aromaten.vlu.html https://en.wikipedia.org/wiki/Cyclooctadecanonaene https://en.wikipedia.org/wiki/Cyclooctatetraene Suggested reading CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module 7: Annulenes Title Cyclophanes, Volume 2 Volume 45 of Organic chemistry Editors Philip M. Keehn, Stuart M. Rosenfeld Edition revised Publisher Elsevier, 2016 ISBN 1483269477, 9781483269474 Title Aromatic Chemistry Volume 13 of Tutorial chemistry texts Authors John D. Hepworth, David R. Waring, Michael J. Waring Contributor Royal Society of Chemistry (Great Britain) Edition illustrated Publisher Royal Society of Chemistry, 2002 ISBN 0854046623, 9780854046621 CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module 7: Annulenes Title Alicyclic Compounds: A Modern Comprehensive Treatise Editor Malcolm Sainsbury Publisher Elsevier, 2016 ISBN 148310091X, 9781483100913 Glossary eehttp://www.physics.rutgers.edu/ugrad/351/oldslides/Lecture13.pdf A Annulenes- monocyclic hydrocarbon without side chains of the general formula CnHn (n is an even number) or CnHn+1 (n is an odd number). Anti-aromaticity- is a characteristic of a cyclic molecule with a π electron system that has higher energy due to the presence of 4n electrons in it. Unlike aromatic compounds, which follow Hückel's rule ([4n+2] π electrons) and are highly stable, anti-aromatic compounds are highly unstable and highly reactive. Aromatic- relating to or denoting organic compounds containing a planar unsaturated ring of atoms which is stabilized by an interaction of the bonds forming the ring, e.g. benzene and its derivatives. CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module 7: Annulenes N Non- aromatic- those compounds which deviate from aromaticity. www.physics.rutgers.edu/ugrad/351/oldslides/Lecture13.pdf Time-Lines Timelines Image 1960 A.D. Franz Sondheimer (17 May 1926 – 11 February 1981) was a British chemist. In 1960 Franz and some other chemists, produced a number of annulenes. Using these annulenes they verified and tested huckel’s rule. They found that most of the annulenes with 4n+2 electrons exhibit aromatic properties. Interesting facts Annulenes are completely conjugated monocyclic hydrocarbons. The IUPAC naming conventions are that annulenes with 7 or more carbon atoms are named as [n]annulene, where n is the number of carbon atoms in their ring, though sometimes the smaller annulenes are referred to using the same notation, and benzene is sometimes referred to simply as annulene. CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module 7: Annulenes The first three annulenes are cyclobutadiene, benzene, and cyclooctatetraene ([8]annulene). Some annulenes, namely cyclobutadiene, cyclodecapentaene or [10]annulene, cyclododecahexaene or [12]annulene and cyclotetradecaheptaene ([14]annulene), are unstable, with cyclobutadiene extremely so. Annulenes may be aromatic (benzene, cyclooctadecanonaene or [18] annulene), non- aromatic ([10]annulene), or anti-aromatic (cyclobutadiene, [12]annulene). Only cyclobutadiene and benzene are fully planar, though [14] and [18]annulene with all trans double bonds (placing the hydrogens inside the ring) can achieve the planar conformation needed for aromaticity, with [14] and [18]annulene following Hückel's rule with 4n+2 π electrons. [14]annulene does exhibit some ring strain due to steric hindrance. Many of the larger annulenes, [18]annulene for example, are large enough to minimize the van der Waals strain of internal hydrogens and thermodynamically qualify as aromatic. However, none of the larger annulenes are as stable as benzene, as their reactivity more closely resembles a conjugated polyene than an aromatic hydrocarbon. In annulynes, one double bond is replaced by a triple bond. Source- https://sussle.org/t/Annulene Case study Comparative molecular orbital study of [6]-, [10]-, and [18]annulenes and the bridged [10]annulenes Robert C. Haddon, Krishnan Raghavachari CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module 7: Annulenes J. Am. Chem. Soc., 1985, 107 (2), pp 289–298 DOI: 10.1021/ja00288a001 Publication Date: January 1985 Source- http://pubs.acs.org/doi/abs/10.1021/ja00288a001 CHEMISTRY Paper No. 1: ORGANIC CHEMISTRY- I (Nature of Bonding and Stereochemistry) Module 7: Annulenes .
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