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annulene wikipedia jump to content main menu main menu move to sidebar hide navigation main page contents current events random article about wikipedia contact us contribute help learn to edit community portal recent changes upload file special pages search search appearance donate create account log in personal tools donate create account log in contents move to sidebar hide top 1 aromaticity 2 gallery 3 see also 4 references 5 external links toggle the table of contents annulene 15 languages العربية বাংলা català deutsch español فارسی français italiano 日本語 한국어 nederlands română русский українська 中文 edit links article talk english read edit view history tools tools move to sidebar hide actions read edit view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikimedia commons wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia completely conjugated monocyclic hydrocarbons not to be confused with aniline structure and afm image of a hexadehydrotribenzo 12 annulene annulenes are monocyclic hydrocarbons that contain the maximum number of non cumulated or conjugated double bonds mancude and their derivatives they have the general formula c n h n when n is an even number or c n h n 1 when n is an odd number the iupac accepts the use of annulene nomenclature in naming carbocyclic ring systems with 7 or more carbon atoms using the name n annulene for the mancude hydrocarbon with n carbon atoms in its ring 1 though in certain contexts e g discussions of aromaticity for different ring sizes smaller rings n 3 to 6 can also be informally referred to as annulenes using this form of nomenclature 1 3 5 7 cyclooctatetraene is 8 annulene and benzene is 6 annulene and occasionally referred to as just annulene 2 3 the discovery that 18 annulene possesses a number of key properties associated with other aromatic molecules was an important development in the understanding of aromaticity as a chemical concept in the related annulynes one double bond is replaced by a triple bond aromaticity edit aromaticity of the even annulenes n aromaticity 4 antiaromatic 6 aromatic 8 nonaromatic 10 nonaromatic 12 weakly antiaromatic 14 weakly aromatic 16 nonaromatic 4 18 aromatic annulenes may be aromatic 6 annulene benzene and 18 annulene non aromatic 8 and 10 annulene or anti aromatic cyclobutadiene 4 annulene cyclobutadiene is the only annulene with considerable antiaromaticity since planarity is unavoidable with 8 annulene the molecule takes on a tub shape that allows it to avoid conjugation of double bonds 10 annulene is of the wrong size to achieve a planar structure in a planar conformation ring strain due to either steric hindrance of internal hydrogens when some double bonds are trans or bond angle distortion when the double bonds are all cis is unavoidable thus it does not exhibit appreciable aromaticity when the annulene is large enough 18 annulene for example there is enough room internally to accommodate hydrogen atoms without significant distortion of bond angles 18 annulene possesses several properties that qualify it as aromatic 5 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 general charged annulene species of the form c 4 n 2 q h 4 n 2 q q n 0 1 2 q 0 1 2 4 n 2 q 3 are aromatic provided a planar conformation can be achieved for instance c 5 h 5 c 3 h 3 and c 8 h 2 8 are all known aromatic species gallery edit cyclobutadiene 4 annulene benzene 6 annulene cyclooctatetraene 8 annulene cyclodecapentaene 10 annulene cyclododecahexaene 12 annulene cyclotetradecaheptaene 14 annulene cyclooctadecanonaene 18 annulene cyclodocosahendecaene 22 annulene see also edit wikimedia commons has media related to annulenes annulyne circulene fulvenes references edit iupac compendium of chemical terminology 5th ed the gold book 2025 online version 2006 annulene doi 10 1351 goldbook a00368 ege s 1994 organic chemistry structure and reactivity 3rd ed d c heath and company dublin city university annulenes archived april 7 2005 at the wayback machine johnson suzanne m paul iain c king g s d 1970 16 annulene the crystal and molecular structure journal of the chemical society b physical organic 643 649 doi 10 1039 j29700000643 issn 0045 6470 oth jean f m bünzli jean claude de julien de zélicourt yves 1974 11 06 the stabilization energy of 18 annulene a thermochemical determination helvetica chimica acta 57 7 2276 2288 bibcode 1974hchac 57 2276o doi 10 1002 hlca 19740570745 issn 0018 019x external links edit nist chemistry webbook 18 annulene structure of 14 and 18 annulene v t e annulenes even numbered cyclobutadiene benzene cyclooctatetraene cyclodecapentaene cyclododecahexaene cyclotetradecaheptaene cyclohexadecaoctaene cyclooctadecanonaene odd numbered cyclopropene cyclopentadiene cycloheptatriene cyclononatetraene compounds in italics are aromatic authority control databases gnd retrieved from https en wikipedia org w index php title annulene oldid 1349290942 categories annulenes physical organic chemistry hidden categories articles with short description short description matches wikidata webarchive template wayback links commons category link is on wikidata this page was last edited on 16 april 2026 at 17 14 utc page was rendered with parsoid text is available under the creative commons attribution sharealike 4 0 license additional terms may apply by using this site you agree to the terms of use and privacy policy wikipedia is a registered trademark of the wikimedia foundation inc a non profit organization privacy policy about wikipedia disclaimers contact wikipedia legal safety contacts code of conduct developers statistics cookie statement mobile view search search toggle the table of contents 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