Editing Aromatic compound (section)

== Non-benzylic arenes ==
Although benzylic arenes are common, non-benzylic compounds are also exceedingly important. Any compound containing a cyclic portion that conforms to [[Hückel's rule]] and is not a benzene derivative can be considered a non-benzylic aromatic compound.<ref name=":43" />

=== Monocyclic arenes ===
Of [[annulene]]s larger than benzene, [12]annulene and [14]annulene are weakly aromatic compounds and [18]annulene, [[Cyclooctadecanonaene]], is aromatic, though strain within the structure causes a slight deviation from the precisely planar structure necessary for aromatic categorization.<ref>{{Cite web |date=2013-10-02 |title=What does "aromatic" really mean? |url=https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Arenes/Properties_of_Arenes/Aromaticity/What_does_aromatic_really_mean |access-date=2023-11-06 |website=Chemistry LibreTexts |language=en}}</ref> Another example of a non-benzylic monocyclic arene is the [[Cyclopropenium ion|cyclopropenyl]] (cyclopropenium cation), which satisfies [[Hückel's rule]] with an n equal to 0.<ref name=":4">{{Cite web |date=2013-10-02 |title=What does "aromatic" really mean? |url=https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Arenes/Properties_of_Arenes/Aromaticity/What_does_aromatic_really_mean |access-date=2023-11-29 |website=Chemistry LibreTexts |language=en}}</ref> Note, only the cationic form of this cyclic propenyl is aromatic, given that neutrality in this compound would violate either the octet rule or [[Hückel's rule]].<ref name=":4" />

Other non-benzylic monocyclic arenes include the aforementioned heteroarenes that can replace carbon atoms with other heteroatoms such as N, O or S.<ref name=":43" /> Common examples of these are the five-membered [[pyrrole]] and six-membered [[pyridine]], both of which have a substituted nitrogen<ref>{{Cite web |date=2020-07-30 |title=4.2: Covalent Bonds |url=https://chem.libretexts.org/Courses/Mount_Aloysius_College/CHEM_100%3A_General_Chemistry_(O'Connor)/04%3A_Covalent_Bonding_and_Simple_Molecular_Compounds/4.02%3A_Covalent_Bonds |access-date=2023-11-06 |website=Chemistry LibreTexts |language=en}}</ref>

=== Polycyclic aromatic hydrocarbons ===
[[Image:Hexabenzocoronene-3D-balls.png|thumb|[[Hexabenzocoronene]] is a large polycyclic aromatic hydrocarbon.]]
{{main|Polycyclic aromatic hydrocarbon}}

[[Polynuclear aromatic hydrocarbon|Polycyclic aromatic hydrocarbons]], also known as polynuclear aromatic compounds (PAHs) are aromatic hydrocarbons that consist of fused [[aromatic]] [[Simple aromatic ring|rings]] and do not contain [[heteroatom]]s or carry [[substituent]]s.<ref>{{Cite journal |last=Fetzer |first=John C. |date=2007-04-16 |title=THE CHEMISTRY AND ANALYSIS OF LARGE PAHs |url=http://www.tandfonline.com/doi/abs/10.1080/10406630701268255 |journal=Polycyclic Aromatic Compounds |language=en |volume=27 |issue=2 |pages=143–162 |doi=10.1080/10406630701268255 |s2cid=97930473 |issn=1040-6638}}</ref> [[Naphthalene]] is the simplest example of a PAH. PAHs occur in [[oil]], [[coal]], and [[tar]] deposits, and are produced as byproducts of fuel burning (whether fossil fuel or biomass).<ref name=":5">"Polycyclic Aromatic Hydrocarbons – Occurrence in foods, dietary exposure and health effects" (PDF). European Commission, Scientific Committee on Food. December 4, 2002. Archived (PDF) from the original on 2022-10-09.</ref> As pollutants, they are of concern because some compounds have been identified as [[carcinogen]]ic, [[mutagen]]ic, and [[teratogen]]ic.<ref name=":6">{{Cite journal |last1=Larsson |first1=Bonny K. |last2=Sahlberg |first2=Greger P. |last3=Eriksson |first3=Anders T. |last4=Busk |first4=Leif A. |date=July 1983 |title=Polycyclic aromatic hydrocarbons in grilled food |url=https://pubs.acs.org/doi/abs/10.1021/jf00118a049 |journal=Journal of Agricultural and Food Chemistry |language=en |volume=31 |issue=4 |pages=867–873 |doi=10.1021/jf00118a049 |pmid=6352775 |bibcode=1983JAFC...31..867L |issn=0021-8561}}</ref><ref>Scientific Opinion of the Panel on Contaminants in the Food Chain on a request from the European

Commission on Marine Biotoxins in Shellfish – Saxitoxin Group. The EFSA Journal (2009) 1019, 1-76.</ref><ref>{{Cite journal |last=Keith |first=Lawrence H. |date=2015-03-15 |title=The Source of U.S. EPA's Sixteen PAH Priority Pollutants |url=https://www.tandfonline.com/doi/full/10.1080/10406638.2014.892886 |journal=Polycyclic Aromatic Compounds |language=en |volume=35 |issue=2–4 |pages=147–160 |doi=10.1080/10406638.2014.892886 |issn=1040-6638}}</ref><ref>{{Cite journal |last1=Thomas |first1=Philippe J. |last2=Newell |first2=Emily E. |last3=Eccles |first3=Kristin |last4=Holloway |first4=Alison C. |last5=Idowu |first5=Ifeoluwa |last6=Xia |first6=Zhe |last7=Hassan |first7=Elizabeth |last8=Tomy |first8=Gregg |last9=Quenneville |first9=Cheryl |date=2021-02-01 |title=Co-exposures to trace elements and polycyclic aromatic compounds (PACs) impacts North American river otter (Lontra canadensis) baculum |journal=Chemosphere |volume=265 |pages=128920 |doi=10.1016/j.chemosphere.2020.128920 |issn=0045-6535|doi-access=free |pmid=33213878 |bibcode=2021Chmsp.26528920T }}</ref> PAHs are also found in cooked foods.<ref name=":5" /> Studies have shown that high levels of PAHs are found, for example, in meat cooked at high temperatures such as grilling or barbecuing, and in smoked fish.<ref name=":5" /><ref name=":6" /> They are also a good [[PAH world hypothesis|candidate molecule to act as a basis for the earliest forms of life]].<ref>{{Cite journal |last1=Ehrenfreund |first1=Pascale |last2=Rasmussen |first2=Steen |last3=Cleaves |first3=James |last4=Chen |first4=Liaohai |date=June 2006 |title=Experimentally Tracing the Key Steps in the Origin of Life: The Aromatic World |url=http://www.liebertpub.com/doi/10.1089/ast.2006.6.490 |journal=Astrobiology |language=en |volume=6 |issue=3 |pages=490–520 |doi=10.1089/ast.2006.6.490 |pmid=16805704 |bibcode=2006AsBio...6..490E |issn=1531-1074}}</ref> In [[graphene]] the PAH motif is extended to large 2D sheets.<ref>{{Cite journal |last1=Wang |first1=Xiao-Ye |last2=Yao |first2=Xuelin |last3=Müllen |first3=Klaus |date=2019-09-01 |title=Polycyclic aromatic hydrocarbons in the graphene era |journal=Science China Chemistry |language=en |volume=62 |issue=9 |pages=1099–1144 |doi=10.1007/s11426-019-9491-2 |s2cid=198333072 |issn=1869-1870|doi-access=free |hdl=21.11116/0000-0004-B547-0 |hdl-access=free }}</ref>