Talk:Polycyclic aromatic hydrocarbon

message: Does anyone know where to find the UV-vis and fluorescence spectra online? These would be very useful.  —Preceding unsigned comment added by 74.247.199.50 (talk) 20:26, 12 July 2010 (UTC)
thread_title: UV-FL Spectra

message: The Polycyclic aromatic hydrocarbon is clear in defining that PAH have no hetero atoms and no substituents. NIST's database seems to agree, as it contains only pure H and C compounds, though their information doesn't seem to include an explicit definition. Here's another definition that agrees with that. However, aromatic hydrocarbon and :Category:Polycyclic aromatic hydrocarbons have a looser definition allowing hetero atoms.
Is one definition more correct than the other? And if the definition of a PAH is the strict one, what is a compound that is aromatic and polycyclic, but has hetero atoms and functional groups called? I'm out of my league with regards to chemical knowledge here, and I don't have any authoritative sources to look it up in at the moment. But it is definitely a conflict among our articles that should be fixed. - Taxman Talk 14:34, July 30, 2005 (UTC)
:Polycyclic aromatic hydrocarbon are hydrocarbons. Hence, they consist of carbon and hydrogen only. --Itub (talk) 12:35, 9 November 2008 (UTC)
thread_title:  PAH definition conflict 

message: I assume that PAHs are carcinogenic/mutagenic due to their ablility to intercalate DNA.  If anyone can confirm a reason for the health effects, it might be good to include it in the article.--24.16.148.75 04:17, 9 July 2006 (UTC)
thread_title:  Method of carcinogenity 

message: (PAHs) are chemical compounds that consist of fused aromatic rings and CAN contain heteroatoms or carry substituents.  
Example: As we begin to produce Ultra Low Sulfur Diesel (less than 15 ppm) in the Americas some of the most difficult to remove sulfur is contained in 4-6 Dimethyl Dibenzothiophene (4-6 DM DBT) or 4-6 DE DBT.  These are both substituted and heteroatom containing PAHs.  Alkyl substitued PAHs are thought to be more toxic than non-substitued PAHs 
ref: http://www.uoguelph.ca/cntc/publicat/science_briefs/2003-09-September-CNTC-Science-Brief.pdf —The preceding unsigned comment was added by 208.251.40.100 (talk • contribs) .
:If the substituent is an alkyl group, it's still a hydrocarbon. I don't see why molecules that contain elements other than hydrogen and carbon should be called hydrocarbons. —Keenan Pepper 22:41, 12 August 2006 (UTC)
thread_title:  PAH can definitely contain heteroatoms or substituents 

message: Having just looked at this discussion, although I have edited the PAH entry and those of some specific compounds, I will give answers and opinions about the various topics. First, the International Union for Pure and Appied Chemistry (IUPAC) nomenclature rules define a polycyclic aromatic hydrocarbon as the core ring structure only. Heteroatom-containing analogues are called polycyclic aromatic compounds, PACs. The "s" is small case for PAHs and PACs according to the guidelines for publication by the American Chemical Society. These are collective plural categories. PAH refers to one compound or is the adjective form, as in a "PAH spectrum". Polycyclic also, according to the IUPAC rules, refers to those of three or more rings, so naphtrhalene is not formally a PAH. An alkyl-substituted PAH is just that, a category in itself, just like a chlorinated PAH. Although an alkyl substituted PAH is a hydrocarbon, it is not formally a PAH. It is an alkyl-substituted PAH since PAH refers only to the multi-ring, fused aromatic core.
The sulfur PACs are commonly abbreviated as S-PACs, so dibenzothiophene - which is one of the compound types in low-sulfur fuels is a S-PAC and not a PAH.
A few minor comments about PAH nomenclature relating to the letters and numbers in the {}. First, they are braces or the square-cornered brackets, not parentheses. Second, numbers are separated by commas - like 1,2,3,4 or 9,10. Letters are not separated by commas if they are refering to continuous faces of the same fused group - like abcd or pqr. If the faces are not contiguous, as in naming two benzo groups on the same core, there are commas separating each group - like a,h or cd,lm.
AS far as mutagenicity/ carcinogenicity (I will use mutagenicity from now on since carcinogenicity is just mutagenicity in a replicated version - a change in the DNA that can be repeated), it is very dependent on structure. The PAH is not itself mutagenic. It is the oxygen-containing metabolites or oxidation products (hydroxyl, epoxide, ketones, etc.) that actually fit into the DNA structure (an adduct) that cause mutation. This lock and key fitting is what determines mutagenicity. Certain shapes in a PAH become the oxygen derivative that binds to the DNA. So substituents may increase the potency, or not. The key is the fit of the oxygenated derivatives into DNA, the intercolation that leads to replicating mutations. The most potent PAH known, so far, is the unsubstituted dibenzo[def,p]chrysene (dibenzo[a,l]pyrene), which is around 2000 times more active than benzo[a]pyrene in an Ames test.
So isomers can differ greatly in mutagenic activity becausae of shape differences. Alkylation generally reduces mutagenicity because the alkyl substituent both changes the shape of the PAH structure and may occupy the active site which prevents the oxygen derivative formation. Additionally longer alkyl groups, C4 or greater, shield the molecule more from oxidation and make it more lipophilic/ hydrophobic, which means less gets into the aqueous environment for metabolism.
Although the NIST database is thorough and well done, it carries no official significance, other than it is a source of structures and information. The authors, Lane Sander and Stephen wise, say so in the preface. The nomenclature is their best attempt at sticking to IUPAC rules. This is also the stance of Chemical Abstracts - they try, but know they are imperfect. You can find differences in naming the same structure between these two, in fact.
If this information needs to be added to the article, I can provide more references. I added my book on PAHs as a reference and it has much about these nomenclature and biological activity topics.
—fetz the chemist
:Bravo Fetz, thank you.  Le Prof Leprof 7272 (talk) 16:43, 10 June 2014 (UTC)
thread_title:  PAH nomenclature and more 

message: The information on nomenclature belongs in an article on nomenclature, rather than here.  This article on PAHs should link to the IUPAC nomenclature of organic chemistry article, and your (Fetz) information could improve that article.  Of course, this article should use compliant names -- see Wikipedia:Naming conventions (chemistry).
The mutagenicity information is noteworthy, hence well worth including in this article, always assuming it complies with Wikipedia policies e.g. WP:OR. yoyo (talk) 18:41, 25 May 2010 (UTC)
thread_title:  Worth inclusion 

message: Must be more deadly if they are actually in your body after eating them. 80.0.116.162 (talk) 22:21, 10 January 2008 (UTC)
thread_title:  Does not mention PAHs from over-cooked meat from BBQs etc 

message: The National Academy of Sciences published a paper in 2002 proving that polycyclic aromatic hydrocarbons require pressures greater than 30 kilobar for their formation which corresponds to a depth of 100 kilometers deep in the earths crust.  No biological molecule can survive at such a depth because it is past the critical temperature of water.
http://www.pnas.org/content/99/17/10976.full?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=genesis+of+hydrocarbons+and+the+origin+of+petroleum&searchid=1085470440708_510&stored_search=&FIRSTINDEX=0
Of course, this will never be allowed in this article because the fascists who edit wikipedia subscribe to medieval theories.Wikkidd (talk) 20:34, 6 July 2008 (UTC)
replies: text: Please keep your POV edit warring in the appropriate articles.  This is not the place to push abiotic oil.  By the way, why don't you understand that just because Kenney and Kutcherov assert something doesn't mean that it has been proven.  Enough geologists and chemists have told you so that maybe you should start being agnostic about the idea.  NJGW (talk) 17:30, 9 July 2008 (UTC)
thread_title:  Formation of Polycyclic Aromatic Hydrocarbons 

message: It hasn't been mentioned yet that PAHs are also created by grilling and similiar types of cooking. I've added a mention plus reference to correct this.NJGW (talk) 03:59, 22 September 2008 (UTC)
thread_title:  Polycyclic Aromatic Hydrocarbons 

message: Should there be a section in this article on Kekulene? (C48H24)  —Preceding unsigned comment added by 205.250.72.175 (talk) 03:49, 22 September 2008 (UTC)
replies: text: A superbenzene? Sounds cool... what's it do? ;)  As long as it's well sourced, not too technical (and hopefully someone has a GFDL picture of the molecule) it could be a good addition.  Maybe some day get it's own article.  NJGW (talk) 03:59, 22 September 2008 (UTC)
thread_title:  Kekulene 

message: Considering that naphtalene has only 2 fused rings and if IUPAC said that only compounds with at least 3 fused rings are PAH (as the page says), why did you add naphtalene in the array with names and formulae ? It has no meaning ? I simply need an explanation because it is written that those compounds are PAH... but naphtalene not.  —Preceding unsigned comment added by 132.210.213.127 (talk) 20:52, 10 January 2011 (UTC)
replies: text: See long discussion above on this very subject.  Le Prof Leprof 7272 (talk) 17:09, 10 June 2014 (UTC)
thread_title:  PAH 

message: For sake of improving the wiki content, the speculation of PAHs toward origin of life is an extrascientific pursuit and ought to be excised from the page.  Respectfully. 128.219.49.9 (talk) 14:27, 17 May 2011 (UTC)
replies: text: FWIW - PAHs, Along With Fullerenes, Have Been Detected In Outer Space(1,2) - Such Molecules Seem Sufficiently Complex To Be Credible Abiogenic Precursor Substances And, via of the PAH world hypothesis, May Lead To An RNA world - And, Afterwards, To Our Present DNA world - As A Result, The Possible Involvement Of PAHs In the Origin Of Life Seems A Worthy Scientific Pursuit - And Worth Mentioning In The PAH Article - In Any Case - Enjoy! :) Drbogdan (talk) 02:22, 18 May 2011 (UTC)
replies: text: Considering that 5 out of 19 refs refer to the origin of life and NASA for one is spending millions on studies I certainly do not see where it is not worth a mention in the lede.  All scientific inquiry starts with speculation. Gandydancer (talk) 04:52, 18 May 2011 (UTC)
replies: text: Please see new Talk section on origin of life text material, same date and editor as this cross-reference.  Le Prof Leprof 7272 (talk) 17:36, 10 June 2014 (UTC)
thread_title:  Introduction 

message: This molecule is in the news because an image of a single molecule has been published (e.g. BBC news site). A new article (also in Did you know) would be timely, but I'm not an organic chemist, so don't feel qualified to do it.
Lots of info at http://www.chemspider.com/Chemical-Structure.19896409.html
Synthesis: Conjugated cyclic hydrocarbons. Part VIII. The benzo[cd]pyrenium cation: synthesis and reactivity. D. H. Reid, W. Bonthrone, J. Chem. Soc., 1965, 5920.
Petergans (talk) 10:15, 28 May 2012 (UTC)
thread_title:  Olimpicene 

message: The article has long had :File:Polycyclic Aromatic Hydrocarbons.png as the lede image. It's pretty, but one of the three structures is cut off (it's not dibenz(ah)anthracene at the bottom, but just a part of that structure) and one does not have an article (benz(e)acephenanthrylene). A better image would have complete molecules (and perhaps drawn more chemically explicitly and without superfluous background color) and cherry-pick notable examples (as defined by having articles on them). DMacks (talk) 05:14, 13 January 2014 (UTC)
replies: text: @ - Thank you for your comments - a benz(e)acephenanthrylene article has been newly created - I agree - a better image would be welcome - in any case - thanks again for your comments - and - Enjoy! :) Drbogdan (talk) 15:36, 5 March 2014 (UTC)
thread_title:  Lede image 

message: I disagree with the article's lead sentence - polycyclic aromatic hydrocarbons (PAHs) are not necessarily fused aromatic rings.  The term for fused aromatic ring compounds is polynuclear aromatic hydrocarbons (PNAs), a subset of PAHs.  The Chem Abstracts guidance in paragraph 147 (2002,and also 2007) mentioned above by Ken the Chemist was cut short; Ken only quoted the first of 4 categories.  The other big category of PAHs is single-bond-connected rings such as biphenyl or terphenyl.  So PNA is not a synonym for PAH.  The class of compounds that are metabolized in the human body to carcinogenic epoxide-derivatized forms (easily hydrolyzed to the alcohol form) is the fused ring systems, PNAs.  Ironically, PNAs are epoxidized in the liver to facilitate their excretion by making them more soluble.  This normal biochemical process backfires.  I will rewrite the beginning of the article, if no one strongly objects. Drbillellis 15:06, 7 May 2014 (UTC)
replies: text: My background isn't chemistry, but I have done research involving PAHs on biological systems, but I'm guessing you'll be basing the description on IUPAC definitions just by looking at the discussions here. Would "bound" be better than "fused"? It seems like the majority of PAHs are fused, either ortho-fused, or ortho- peri-fused, and only some are aryl, like biphenyl. With that in mind, would it be better to address it that way and go into it in the body? Esoxidtalk•contribs 23:56, 7 May 2014 (UTC)
replies: text: Bound is not better than fused. Fused is the standard language, and bound has various distinct chemical meanings depending on context. Le Prof Leprof 7272 (talk) 17:32, 10 June 2014 (UTC)

text: Add my edit here. The 2007 CAS refers to what I called aryl, as ring assemblies. Where can I find a PNA (polynuclear aromatic hydrocarbon) definition? I've found papers where PAHs are referred to as polynuclear aromatic hydrocarbons, but not formal definitions or references to PNAs. Esoxidtalk•contribs 00:15, 8 May 2014 (UTC)
replies: text: This is a site where the terms are used: http://www.docbrown.info/page07/Aromatics.htm.  I regret the author's rather sloppy equalization of terms.  My background is organic chemistry (PhD, Johns Hopkins U. 1981); my preference for terms comes from my advisors and co-workers in grad school, and in my on-the-job training in environmental toxicology of coal tars and other sources of carcinogenic fused-ring aromatics such as the cigarette smoke PNA carcinogen benzo[a]pyrene. The preferred term for PNAs, which share one or more "sides" (2 adjacent carbons) is "fused" rings. The term "bound" is inadequate - it suggests only a single bond between.  The nature of fused ring systems is the ease with which the body's liver enzymes can epoxidize one face (side), intending to make the foreign chemical more soluble and excretable, but inadvertently making it into a DNA/RNA attacking carcinogen. The extensive p-electron array of fused rings facilitates this reaction.  Drbillellis 12:24, 5 June 2014 (UTC)
replies: text: All good insights, and valuable here. Subject matter experts actually editing in their specific articles of interest is about as good as it can be here. (I am PhD Chem/pharma and nat products, and so am a little out of my waters here; but as teaching and research Prof, have broader experience that undergirds my general responses.) Note, FYI, doc brown website is not an acceptable source here. Bottom line on the broader discussion, any usage that you can find that is substantiated by two or more reputable secondary sources (e.g., reviews or book chapters) reflects usage that is likely broad enough here to be included. Note, there are IUPAC-only folks that patrol chemistry pages, but I will support you in introducing other usage directions if they are substantiated by the referencing I indicate. Le Prof Leprof 7272 (talk) 17:32, 10 June 2014 (UTC)

text: Most of my work was in the biotransformation of PAHs (or PNAs) and effects on marine biological communities (vertebrates and inverts), so I'm at least familiar with effects, not necessarily the entire biochemical mechanisms, so my literature library is full of papers that use the term but give no definition of PNAs. The others just use PAH as a collective term, since it's usually just that, both high-molecular weight and low-molecular weight PAHs from some point-source like former wood treatment facilities. Thanks for the information.Esoxidtalk•contribs 20:16, 5 June 2014 (UTC)
replies: text: This "PAH as collective term" is just the sort of "usage v. nomenclature" reality that I make mention of in the foregoing discussion far above. Le Prof Leprof 7272 (talk) 17:32, 10 June 2014 (UTC)

text: Guys, please review the long foregoing talk, digesting all, before starting bold nomenclature/usage editing, or restarting discussions (that may have already, in some respects, have reached a conclusion. See, in particular, the section above, "PAH definition conflict" and sections preceding it, for a long discussion on the matters you are raising here. (Click here  and scroll up.) If after reading all of this, there is still a proposal to make about a change, please create a new section and make a proposal, and let it sit for a time before making bold edits. Even better, ping the two chemists that argued extensively above (if they are still around). New edits always welcome, but so little time in life, have no interest in reinventing this Wikiwheel.  Cheers, Le Prof Leprof 7272 (talk) 17:32, 10 June 2014 (UTC)
thread_title:  Meaning of "Polycyclic" 

message: I do not agree with the IP editor 128... above, nor can anyone believe he argues based on the preponderance of scientific opinion and available sources. Moreover, the section in question is one of the most richly referenced and up to date sections in the article (a clear positive). 
However, this section is now 1/8th of the article volume, 11 of the 36 citations, and 23 of the 49 inline citations. This is clearly disproportionate, so it is clear, relative to the other areas where PAHs have historic and current chemical, toxicologic, and other literature presences, that the article has begun to give this area attention beyond what it should in a general article. 
At the same time, this astrophysical flare-up has created/furthered a pattern of relying on primary sources and news reports to a degree that is not acceptable at WP. There are certain cases where primary sources are necessary, but secondary sources—reviews, book chapters, etc.—are far preferred in WP policies and guidelines (akin to writing history articles from books by noted historians, and not from newspaper articles). And news reports are used in science sourcing only for establishing that the scientific event was considered newsworthy, and not for sourcing the scientific facts. Press releases are not reliable sources of independent scientific information, at all (because they do an end around journalistic norms that are applied in taking the press release information and doing the news story). 
So, I will begin to edit this section, to reduce its volume, in part to move it toward being based on reliable secondary sources, leaving in as appropriate statements of the newsworthiness of the discoveries as the subjects require and sourcing supports. As well, any redundancies in sourcing will be reduced; in particular, the lede should summarize statements already made in the main body, and so does not need to be richly sourced (if the main body is). Keep an eye. Also will ping the editors placing this all, when I begin.  Cheers.  Le Prof Leprof 7272 (talk) 18:00, 10 June 2014 (UTC)
replies: text: I am OK with shortening the "Origins of life" section. After all, it already has a hat directing it to the main article "PAH world hypothesis"; also, we are supposed to only include a summary of it when linked to its main parent article. Cheers, BatteryIncluded (talk) 20:42, 10 June 2014 (UTC)
replies: text:  Please, @BatteryIncluded, you and @User:Sbharris take a whack, and I will help as well. I want you guys to have your say, for I am merciless with unsourced and speculative material once I get started. I want to make sure your voices are heard, if you have time and interest.  Le Prof  Leprof 7272 (talk) 17:07, 12 June 2014 (UTC)

text:  Agree with Leprof and BatteryIncluded, per WP:SS. A short summary with the main article as we have, is enough. I would shorten the section to two or three paragraphs, since the info is all at the main PAH world hypothesis article. I will admit that some of this is my own prejudice-- I would feel differently if I thought that PAHs (even the proper fused flat polycyclic kind) were some kind of magic solution for the primary problem of life origin, which is that phosphate polymers (indeed all polymers made by -OH OH- condensation and water expulsion, including proteins and RNA-AA hybrids) are not stable in water. So that hurts the idea of any sort of standard prebiotic watery soup. Somebody found these PAH things in space (gosh it must smell like a bar lounge and backyard barbecue out there) and erected a whole rich fantasy world based on them (PAH world hypothesis), but it's all very airy hypothesis with no evidence at this point, and even if "PAH worlds" exist (and smell like George Foreman and George Burns), they STILL don't solve a primary problem. Perhaps they help nucleotide bases stack a bit better.  However, if PAH's are really 20% of the universe's carbon that exists in dust between stars, and perhaps are a primordial carbon component of our solar system and a starting material for tholins, then I think that they should get more space in the carbon article in the Universe section, rather than here. After all, we don't KNOW they have anything to do with life-- it's a very whisp of a suggestion. We do know there's a hell of a lot of them out there in space, though. So that fact should get the bulk of the play HERE in this PAH article, not the (VERY) speculative life connection (which for the third time, indeed has its own article for those who want to play with it). SBHarris 21:44, 10 June 2014 (UTC)
replies: text:  Thanks for responsiveness and feedback, both. And good point in re Carbon article, @User:Sbharris. I am also a "what's the latest world we can imagine" skeptic, but I understand the game—as a former academic—that like a homebuilder whose job is to produce homes, such is what we/they do (produce ideas, some novel, some not so). It is indeed remarkable, the 20% number, but of that—a computed number without reported error—I am suspicious, and will look to it to see what the original pub actually said. But, if your George Foreman will produce micrograms from incomplete combustion, surely a fiery planet-creating event can give us a comparable bit of char. (Technically, chemically, had the PAH research remained focused on temperature I would be more skeptical, but combustion when short of oxygen is a stellar scenario that is imaginable.) More generally, I think at times that the nature of origins research makes it all a bit too easy. There was, decades ago when I worked in this field, an article that proposed earth had been covered by a 1-10m oil slick during the period of interest to AI Oparin et al., see this: . I was going to tell you this idea withered on the vine, as I anticipate the PAHs-are-the-key arguments will. But then I found this, see . mdr Real value of it all?  Well, I left the area, and went to work in infectious disease drug discovery, so my vote with my feet tells you what I think, at heart. Cheers, and look forward to a collaborative re-write of this section.  Le Prof  Leprof 7272 (talk) 17:07, 12 June 2014 (UTC)

text: This seems to be a good working team, and I would like to highlight that Dr Bogdan has worked on this subject in real life, and that he is the most gentle editor I have come across. Bogdan, are you OK with condensing the "Origins of Life" section in this article? I admit I am not very familiar with the PAH world hypothesis, but this discussion should be transferred there. Cheers, BatteryIncluded (talk) 00:05, 13 June 2014 (UTC)
replies: text: @ - Thank you for your comments - they're *very* much appreciated - in some ways, I may be warming up to some of this at the moment - *entirely* ok with me if anyone wishes to present some ideas of course - yes, I have some modest research/publication experience (some years ago) with PAHs - mostly related to chemical carcinogenesis at the DNA level - but know there's much more to learn - Thanks again for your comments - and - Enjoy! :) Drbogdan (talk) 00:45, 13 June 2014 (UTC)

text: From what I know about polynuclear aromatic hydrocarbons (PNAs), I strongly believe that there is only a very tenuous link between the origin of life and PNAs.  The mention of transformation, oxygenation, and hydroxylation to derive amino acids, proteins, and nucleotides is almost laughable.  PNAs would have to be broken down almost completely, then reacted with ammonia or an amine of some sort to arrive at most amino acids.  Proteins are just chains of amino acids, most of which have no aromatic rings at all.  The chemicals found in celestial objects include ammonia, water, carbon monoxide, hydrogen cyanide, and carbon dioxide - these are reasonable building blocks for amino acids, proteins, and nucleotides.  The objection raised above, about the presence of water being a problem for biogenesis overlooks this: hydrolysis is reversible, and at equilibrium conditions, both reactants and products co-exist, even in water.  My personal opinion is this: PNAs adsorbed to the surface of silicate particles (the latter also found in celestial objects) could very well have been catalysts (ie. more of a template and not a reactant) for the biogenetic reactions of NH3, H2O, CO, HCN, and CO2 to form life precursor chemicals. I think that the astro-professionals who think that PNAs, because they are complex, are life precursors, reveal an embarrassing ignorance of bio-organic chemistry.  Keep in mind - the original Urey-Miller biogenesis experiments used these precursors: water, methane, carbon dioxide, and ammonia, with electrical discharges as the energy source.  Amino acids were found in the product solution; subsequent experiments by other researchers found nucleotides, too. Keep this in mind - the body synthesizes proteins and nucleotides in a thoroughly aqueous environment at body temperature, while PNAs are synthesized under oxygen-deficient high-temperature conditions, and tend to deposit on the surface of silicate dust (in celestial environments) or on soot (from incomplete combustion on earth).  Drbillellis 19:52, 12 September 2014 (UTC)
replies: text: @Drbogdan "This report was considered a controversial hypothesis that as nebulae of the same type as the Red Rectangle approach the ends of their lives, convection currents cause carbon and hydrogen in the nebulae's cores to get caught in stellar winds, and radiate outward." The above unparseable sentence appears in the current version of the Origins of Life section. What does it even mean? Larry Koenigsberg (talk) 16:42, 13 July 2022 (UTC)
replies: text:  and others - Thanks for your comments - interesting - not sure at the moment - may have to do some homework with this at the next opportunity - Comments Welcome about this from other editors of course - in any case - Thanks for your comments - and - Stay Safe and Healthy - Drbogdan (talk) 16:58, 13 July 2022 (UTC)
thread_title:  Will be editing Origins of Life section 

message: The subsection on "Detection and optical properties" is listed within "Human health", but the content appears to be about analytical chemistry methods and physical properties of PAHs. I propose moving it outside of "Human health" to its own section. Does this seem reasonable? I'm happy to make the adjustment myself, but this page has a lot of active editors and I don't want to intervene inappropriately.  -- E.Thorsos (talk) 04:43, 12 August 2014 (UTC)
thread_title:  Move "Detection and optical properties" subsection to its own section? 

message: stick more to the topic and should be more specific .  — Preceding unsigned comment added by 106.51.141.67 (talk) 09:36, 9 August 2015 (UTC)
thread_title:  small change 

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thread_title:  External links modified 

message: In consultation with my colleagues whose research focuses on PAH carcinogenesis and ecotoxicity, I have drafted content that reorganizes and expands information about sources of PAHs, human exposure, health effects, and ecotoxicology. As I format references, etc., I have posted this draft to my sandbox. This update may be too detailed, and I welcome comments before posting. E.Thorsos (talk) 01:05, 3 February 2016 (UTC)
thread_title:  Proposed expansion of PAH sources, distribution, toxicity 

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thread_title:  External links modified 

message: This section talks about three- and four-ring molecules (phenanthrene, anthracene, and chrysene), however I believe there is an error with part of this. The (unsourced) text of the article reads: "Three Clar structures with two sextets each are present in the four-ring chrysene structure: one having sextets in the first and third rings, one in the second and fourth rings, and one in the first and fourth rings." The accompanying image does indeed show three different structures. However, the first two (the "first and third" and "second and fourth" structures) appear to be identical by a 180 degree rotation. Unless there was a heteroatom or substituent to differentiate between the two, would these structures not be identical, thus resulting in only two different Clar structures? I admit I am not a chemist so I may be missing something. For what it's worth, the article on chrysene itself does not mention any of this at all. Lumberjane Lilly (talk) 18:24, 8 May 2024 (UTC)
replies: text: It's true that some of the structures appear as rotations or flips of each other. That is just an effect of the the molecule being symmetric. Drawing distinct resonance structures is already a bit of a fiction (see Resonance (chemistry)), and it relies on the atoms remaining in fixed locations while the bonds are re-positioned. One could just as well label a certain carbon atom as a specific isotope. DMacks (talk) 02:16, 9 May 2024 (UTC)
thread_title:  Error in "Bonding and aromaticity" section