cyclotetradecaheptaene
{{chembox
| Watchedfields = changed
| verifiedrevid = 443551114
| Name = Cyclotetradecaheptaene
| ImageFileL1 = (14)Annulene.svg
|ImageFileR1=(14)Annulene-3D-balls.png
| IUPACName = (1E,3Z,5E,7Z,9E,11E,13Z)-cyclotetradeca-1,3,5,7,9,11,13-heptaene
| OtherNames = [14]Annulene
|Section1={{Chembox Identifiers
| PubChem = 11988275
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 10160742
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 37523
| SMILES = C1C=CC=CC=CC=CC=CC=CC=1
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI=1S/C14H14/c1-2-4-6-8-10-12-14-13-11-9-7-5-3-1/h1-14H/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-,14-13-
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = RYQWRHUSMUEYST-ILUIUFOYSA-N
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 2873-14-5
| RTECS =
}}
|Section2={{Chembox Properties
| C=14 | H=14
| Appearance = dark-red needle-like crytals
| Density =
| Solubility = Insoluble
| SolubleOther = Soluble
| Solvent = benzene
| MeltingPt =
| BoilingPt =
| pKa =
| pKb =
| Viscosity =
}}
|Section3={{Chembox Structure
| MolShape =
| Coordination =
| CrystalStruct = monoclinic
| Dipole =
| SpaceGroup = P21/c, No. 14
| LattConst_a = 8.640 Å
| LattConst_b = 4.376 Å
| LattConst_c = 14.997 Å
| LattConst_beta = 106
| UnitCellFormulas = 2 molecules per cell
}}
|Section7={{Chembox Hazards
| ExternalSDS =
| MainHazards = Flammable, reactive
| FlashPt =
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|Section8={{Chembox Related
| OtherAnions =
| OtherCations =
| OtherCompounds =
}}
}}
Cyclotetradecaheptaene, often referred to as [14]annulene, is a hydrocarbon with molecular formula C14H14, which played an important role in the development of criteria (Hückel's rule) for aromaticity, a stabilizing property of central importance in physical organic chemistry. It forms dark-red needle-like crystals.{{cite journal|last=Chiang|first=Chian C.|last2=Paul|first2=Iain C.|title=Crystal and Molecular Structure of [14]Annulene|journal=J. Am. Chem. Soc.|year=1972|volume=94|issue=13|pages=4741–4743|doi=10.1021/ja00768a058}}
Structure and aromaticity
Although the conjugated ring of [14]annulene contains 4n+2 electrons, it only exhibits limited evidence for being aromatic. It does not fully conform to Hückel's rule because none of its cis/trans isomers can adopt a completely planar conformation due to crowding of the interior hydrogens.{{cite book | title = Aromatic Character and Aromaticity | page = 96 | author = G. M. Badger | publisher = Cambridge University Press}} There is evidence that it has two isomeric forms of comparable stability (trans, cis, trans, cis, trans, trans, cis- with four interior hydrogens (shown in the infobox) and trans, cis, trans, cis, trans, cis, cis- with three interior hydrogens) which rapidly interconvert at room temperature but can be observed at low temperature by NMR.{{Cite book|url=https://archive.org/details/mechanismtheoryi000321|title=Mechanism and theory in organic chemistry|last=H.|first=Lowry, Thomas|date=1987|publisher=Harper & Row|others=Richardson, Kathleen Schueller.|isbn=0060440848|edition=3rd|location=New York|oclc=14214254|url-access=registration}} Its 1H NMR spectrum shows evidence of aromatic ring currents that result in an upfield shift for the interior hydrogens. In contrast, the corresponding [12]- and [16]annulenes, which are weakly antiaromatic or nonaromatic, have downfield shifted interior hydrogens. However, unlike the undoubtedly aromatic [18]annulene, [14]annulene does not bear the hallmark aromatic property of chemical stability, and it quickly decomposes when exposed to light and air.{{cite journal | doi = 10.1021/ja01506a061| title = Unsaturated Macrocyclic Compounds. XV. Cyclotetradecaheptaene| journal = Journal of the American Chemical Society| volume = 82| issue = 21| pages = 5765–5766| year = 1960| last1 = Sondheimer| first1 = Franz| last2 = Gaoni| first2 = Yehiel}}