Chembox ImageFile 18 Annulene.svg ImageSize 170px ImageName Skeletal formula ImageFile1 18 Annulene 3D balls.png ImageSize1 210px ImageName1 Ball and stick model IUPACName OtherNames Section1 Chembox Identifiers CASNo 2040 73 5 PubChem SMILES InChI 1S C18H18 c1 2 4 6 8 10 12 14 16 18 17 15 13 11 9 7 5 3 1 h1 18H b2 1 ,3 1 ,4 2 ,5 3 ,6 4 ,7 5 ,8 6 ,9 7 ,10 8 ,11 9 ,12 10 ,13 11 ,14 12 ,15 13 ,16 14 ,17 15 ,18 16 ,18 17 InChIKey STQWAGYDANTDNA DWSNDWDZSA N Section2 Chembox Properties C 18 H 18 MolarMass Appearance Density MeltingPt BoilingPt Solubility Section3 Chembox Hazards MainHazards FlashPt Autoignition Cyclooctadecanonaene or 18 annulene is an annulene with chemical formula C sub 18 sub H sub 18 sub . This hydrocarbon obeys H ckel s rule and is therefore an aromatic compound. The compound was first synthesised by Franz Sondheimer . ref In the literature and some internet references Sondheimer is misspelled as Sandheimer. ref The original synthesis started by the Eglinton reaction of the di alkyne 1,5 hexadiyne with copper II acetate in pyridine to give the trimer, followed by deprotonation and isomerization with potassium butanol tert butoxide in Tert Butanol tert butanol and was concluded with hydrogen organic reduction with the Lindlar catalyst . ref cite journal title Unsaturated Macrocyclic Compounds. XXIII. The Synthesis of the Fully Conjugated Macrocyclic Polyenes Cyclooctadecanonaene 18 Annulene , Cyclotetracosadodecaene 24 Annulene , and Cyclotriacontapentadecaene 30 Annulene . author Sondheimer, F., Wolovsky, R. and Amiel, Y. journal J. Am. Chem. Soc. year 1962 volume 68 issue 2 pages 274 284 doi 10.1021 ja00861a030 ref ref OrgSynth title nowiki 18 Annulene nowiki author K. St ckel and F. Sondheimer collvol 6 collvolpages 68 year 1988 prep cv6p0068 ref References references Category Annulenes ar fr Cyclooctad canona ne nl Cyclooctadecanonaeen ja zh 18 ... more details
The molecular formula C sub 18 sub H sub 18 sub molar mass 234.33 g mol may refer to Cyclooctadecanonaene Retene MolFormDisambig C sub 18 sub H sub 18 sub fr C18H18 ... more details
File 14 Annulene.svg right thumb 14 Annulene. File 18 Annulene.svg right thumb 18 Annulene. Annulenes are completely Conjugated system conjugated Cyclic compound monocyclic hydrocarbon s. They have the general formula C sub n sub H sub n sub when n is an even number or C sub n sub H sub n 1 sub when n is an odd number . The IUPAC nomenclature IUPAC naming conventions are that annulenes with 7 or more carbon atoms are named as n annulene, where n is the number of carbon atom s in their ring, ref GoldBookRef title annulene file A00368 ref though sometimes the smaller annulenes are referred to using the same notation, and benzene is sometimes referred to simply as annulene. ref Ege, S. 1994 Organic Chemistry Structure and Reactivity 3rd ed. D.C. Heath and Company ref ref Dublin City University http www.dcu.ie chemist pratt annulene annulene.htm Annulenes ref 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, 14 annulene, cyclooctadecanonaene or 18 annulene , non aromatic 10 annulene , or anti aromatic cyclobutadiene . Only cyclobutadiene and benzene are fully Plane geometry 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 H ckel s rule with 4n 2 Pi bond electrons . 14 annulene does exhibit some ring strain due to steric hindrance . Many of the larger annulenes, 18 annuelene 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 ... more details
In organic chemistry , a carbomer is an expanded molecule obtained by insertion of a C sub 2 sub unit in a given molecule. ref Carbomers. I. A general concept of expanded molecules Remi Chauvin Tetrahedron Letters Volume 36, Issue 3 , 16 January 1995 , Pages 397 400 doi 10.1016 0040 4039 94 02275 G ref Carbomers differ from their templates in size but not in symmetry when each C C single bond is replaced by at least one alkyne bond, and when a double bond is replaced by an allene bond. The size of the carbomer will continue to increase when more alkyne bonds are introduced and for this reason carbomers are also called carbo sup n sup molecules , where n is the number of acetylene or allene groups in an n expansion unit. This concept, devised by R mi Chauvin in 1995, is aimed at introducing new chemical properties for existing chemical motifs. Image Carbo benzene.png 500px carbo benzene Two representations exist for carbo benzene written as an Cyclooctadecanonaene 18 annulene derivative 1,2,4,5,7,8,I0,11,13,14,16,17 dodecadehydro 18 annulene , one has the aromatic core of benzene expanded, and one has the hydrogen substituent s expanded. The substituted benzene derivative hexaethynylbenzene is a known compound, ref Hexaethynylbenzene Rainer Diercks, James C. Armstrong, Roland Boese, K. Peter C. Vollhardt. Hexaethynylbenzene. Angewandte Chemie International . 1986 25 3 268 269. DOI 10.1002 anie.198602681 ref and the core expanded molecule also exists, although with the hydrogen atoms replaced by phenyl groups. ref Synthesis of the first 3,6,9,15,18,18 hexa substituted 1,2,4,5,7,8,10,11,13,14,16,17 dodecadehydro 18 annulenes with D6h symmetry Yoshiyuki Kuwatani, Naoto Watanabe and Ikuo Ueda Tetrahedron Letters Volume 36, Issue 1 , 2 January 1995 , Pages 119 122 doi 10.1016 0040 4039 94 02181 A ref The final step in its organic synthesis is reaction of the triol with stannous chloride and hydrochloric acid in diethyl ether . Image CarbobenzeneSynthesis.png 400px carbo b ... more details
about aromatic chemistry the meteorological effect Ring current Image Aromatic ring current 2.png thumb right 200px A diagram of an aromatic ring current. B sub 0 sub is the applied magnetic field, the red arrow indicating its direction. The orange ring shows the direction of the ring current, and the purple rings show the direction of the electromagnetic induction induced magnetic field. An aromatic ring current is an effect observed in aromaticity aromatic molecules such as benzene and naphthalene . If a magnetic field is directed perpendicular to the plane of the aromatic system, a ring current is induced in the delocalized pi bond electrons of the aromatic ring. ref The induced magnetic field in cyclic molecules. Merino, G. Heine, T. Seifert, G. Chem. Eur. J. 2004 10 4367 4371. DOI 10.1002 chem.200400457 ref This is a direct consequence of Amp re s law since the electrons involved are free to circulate, rather than being localized in bonds as they would be in most non aromatic molecules, they respond much more strongly to the magnetic field. Aromatic ring currents are relevant to NMR spectroscopy , as they dramatically influence the chemical shift s of carbon 13 sup 13 sup C and hydrogen atom sup 1 sup H atomic nucleus nuclei in aromatic molecules, ref Aromaticity and Ring Currents Gomes , J. A. N. F. Mallion, R. B. Chem. Rev. Review 2001 101 5 1349 1384. DOI 10.1021 cr990323h ref as well as in any organic or inorganic aromatic molecule. The effect helps distinguish these nuclear environments and is therefore of great use in molecular structure determination. In benzene, the ring protons experience deshielding because the induced magnetic field has the same direction as the external field and their chemical shift is 7.3 ppm compared to 5.6 to the vinylic proton in cyclohexene . In contrast any proton inside the aromatic ring experiences shielding NMR shielding because both fields are in opposite direction. This effect can be observed in cyclooctadecanonaene 18 ... more details
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