Questions tagged [aromaticity]

For questions about the concept of aromaticity. Do not use for reactions of aromatic compounds.

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Why is selenophene aromatic?

According to Wikipedia, The selenophene molecule is flat and aromatic. Being aromatic, it undergoes electrophilic substitution reactions at the 2- or 2,5-positions. These reactions are slower than ...
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Why is abstraction of Hydrogen Rate determining step in sulphonation and iodination?

I have studied that formation of wheland intermediate is the rate determining step in most EAS reactions. Since here aromaticity is lost. However in sulfonation and iodination, abstraction of ...
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Aromaticity of 1,4-Dioxin

Structure of 1,4-dioxin is: Wikipedia page says that it is non-aromatic. Pubchem page shows its structure is planar. In a planar structure, obviously there will be 8 (= $4n$) pi electrons in ...
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How many π-electrons are there in 2-methylene-2H-pyran?

I thought that the structure will be aromatic and stabilised because one of the lone pairs being delocalised with the help of conjugated double bond system but still only 3 π-bonds will be present at ...
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Why do electron-withdrawing groups deshield outer ring protons?

I understand that ring protons experience deshielding because the induced magnetic field (outside the ring) has the same direction as the external applied field, but shouldn't electron withdrawing ...
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How can Phthalocyanine be aromatic when it is not planar? [closed]

Even as Hückel's rule is not applicable in every scenario, especially in metallic clusters, it seems that organic structure need to be planar to show aromaticity. That being the case, Pubchem's ...
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Effect of substituents on aromatic character

Does the presence of substituents (electron withdrawing or electron donating) on an aromatic system have any effect on the aromatic character? In other words, would it be correct to say that benzene ...
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Why is the synthesis of graphene through alkyne trimerization not viable?

I have been looking for a rationale on this as massive polycyclic aromatic hydrocarbons have been synthesized this way, and with Graphene just being an indefinite expansion of aromatic rings, this has ...
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Is pyrene aromatic despite failing Hückel's rule?

Pyrene doesn't seem to be aromatic. However, sources claim that it is aromatic. Considerations: Pyrene is cyclic. ✓ Pyrene is flat (planar). ✓ Pyrene has 16 π electrons. Every atom in the ring ...
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Aromaticity in cyclic ketones

I have read that, cycloprop-2-ene-1-one is aromatic and cyclopent-2,4-dien-1-one is antiaromatic. Basically this is visualized by visualizing the resonance structures of this. Similarly if I apply ...
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Aromaticity of fused rings

I understood how to find aromatic nature of single aromatic rings (like benzene) or that of combination of rings which are independently aromatic, such that the electrons of one ring do not enter into ...
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Is the cyclopropenyl anion antiaromatic?

According to my book, a compound is antiaromatic if it is cyclic, planar, and possesses a fully conjugated system of p-orbitals with $4n$ π-electrons. However, I have also been told that the ...
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Do contiguous monolayer aromatic structures retain the same magnetic susceptibility as the core constituents?

As the synthesis of Porphyrin monolayer strips is achievable, retaining the core aromaticity of the tetrapyrrole; does it still retain the same value of magnetic susceptibility of porphyrin? Does this ...
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Is the lone electron pair of an amide nitrogen part of the π system when building a Hückel matrix?

Is the lone electron pair of the nitrogen atom part of the conjugated π system in the α,β-unsaturated amide pictured below? Is there a general rule for choosing when to include a nitrogen atom in a ...
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Reaction of cyclooctatetraene with sulfuric acid

Problem The correct statement is (A) P & Q are aromatic compound and Q has $\mathrm{sp^3}$-hybridized carbon atom. (B) P is aromatic with 10 π electrons and Q is aromatic with 2 π electrons. (C) ...
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Finding the major contributing tautomer of 1-(propan-2-yl)-1,2,3,5-tetrahydro-6H-pyrazolo[3,4-b]pyridin-6-one [closed]

I am having a problem generating the correct tautomer for 1-(propan-2-yl)-1,2,3,5-tetrahydro-6H-pyrazolo[3,4-b]pyridin-6-one. I am told by my collaborator that the one I am generating is wrong. I am ...
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What is quasi-aromaticity?

During my study of aromaticity, I came through this topic of quasi-aromaticity. Can you please elaborate what Quasi aromatic compounds are and how are they designated?
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Nitrogen with shortest bond length in histidine?

The question asks what nitrogen in the ring of histidine has the shortest bond length. I was thinking that since it has resonance, the initial thought of the nitrogen with the $\pi$ bond is incorrect. ...
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Why is the polarity of the B-N bonds in borazine the reason for its reduced delocalisation of π electrons?

My professor mentioned that borazine is aromatic, but not as much as, say, benzene. The reason he gave for this was that the B-N bonds in borazine, being polar, inhibit resonance. He also mentioned ...
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158 views

Why is the tropylium anion non-aromatic? [duplicate]

Recently I came across a question asking which compounds are anti-aromatic. This was one of the options: I’m confused as this is not an answer. I think the lone pair electrons on the carbanion ...
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Is [7]сirculene aromatic or anti-aromatic?

This compound is called [7]circulene and is one of the examples of non-planar aromatic systems (1). From the first overview of this compound, it is observed that there are 7 benzene rings so one would ...
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Bond lengths in Fullerenes [duplicate]

I came across this about fullerenes- All carbon atoms are equal and the undergo sp2 hybridisation. Each carbon atom forms three sigma bonds with three other carbon atoms. The remaining electron at ...
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Is an antiaromatic compound more stable than a non-aromatic compound because of more conjugation?

(image from a LibreTexts page (archive link)) It is shown that the antiaromatic compound is more stable than the non aromatic compounds 2 and 3 because of a more conjugated system. Here's the exact ...
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Applying Huckel's rule to non-planar compounds

Which of the following compounds is aromatic? From the 4n+2 rule, it must be either option 2 or 4. The answer given in my book is option 4. Why? I think It might be due to one being planar and ...
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What is the double bond equivalence of the following compound?

What is the double bond equivalence of the given compound? The given answer is 14 (8 pi electrons and 6 rings = 14 DBE). But why isn't the lone pair on nitrogen considered?? The lone pair on nitrogen ...
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Why is quinone mono oxime more stable than 4-nitrosophenol?

When we do nitrosation of phenols, we get para-nitrosophenol as the major product, which tautomerises to quinone mono oxime. This article states that it largely exists in the quinonoid form. My ...
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Aromatic Character in Percentage?

I was just searching whether Uracil is aromatic or not and in this link$^1$ it is said that (from the abstract): High-level computational methods were tested for the enthalpy of hydrogenation of ...
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Why is porphyrin aromatic?

I was asked which of the following were aromatic: My understanding of aromatic nature is, that the molecule must be cyclic, planar, every atom in the ring must be sp2-hybridized and the molecule must ...
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1answer
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Bonding in 1,4-dihydro-1,4-diborinine

In most aromatic compounds (e.g. benzene), their $\pi$-bonding molecular orbitals are completely occupied and their antibonding molecular orbitals are unoccupied. I'm wondering if there are any ...
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Aromaticity of Caffeine

In the Caffeine molecule, is aromaticity confined only to the 5 membered ring? The entire molecule is planar and the 6 membered ring also seems to have 6π electrons. The entire molecule has 10π ...
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How is 4H‐1,4‐oxazocine aromatic?

I’ve found 4H‐1,4‐oxazocine in my chemistry book and I’m perplex as it states as aromatic: I can count 6 electrons on p orbitals which could satisfy Hückel’s $n = 1,$ but the oxygen is sp3-hybridized....
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Is cycloheptatriene aromatic or not?

Is cyclohepta-1,3,5-triene aromatic? I think it should not be, because even though the π-system possesses six π-electrons, the conjugation is not complete around the ring.
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Why is 11-oxabicyclo(4.4.1)undeca-1,3,5,7,9-pentaene aromatic?

I have been told by my instructors that for a compound to be aromatic, it must be planar. In this given molecule the oxygen seems to be out of the plane of the conjugated system: how can it still be ...
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Is azonine planar?

I came across aza[9]-annulene, which is given to be aromatic. I can clearly see it follows Hückel's rule with 8 π-electrons in the ring and the lone pair of nitrogen. But the thing that concerns me ...
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How come Cyclopropenylhydroxide exists and not cyclopropenol?

I'm currently studying aromatic compounds via online recorded lectures, and my teacher brought up about cyclopropenol and cyclopropenylhydroxide while teaching carbocylic non benzenoid compounds. He ...
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Does cyclooctatetraene also have a diradical anti-aromatic electronic state?

I read that the molecular orbital diagram of cyclobutadiene predicts that it should have a diradical nature as it has two unpaired electrons in two degenerate non bonding orbitals (one in each). Why ...
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How is the aromaticity in graphene different from the aromaticity in benzene?

The web page Aromaticity in Graphene and other 2-D Systems begins: I. Graphene While the σ-bonding in graphene is assumed to be a rigid honeycomb framework built out of two-center two-electron (2c-2e)...
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What about the aromaticity of cyclopropenylidene?

Here's a compound which we have to tell whether it's aromatic or not. Drawing pi-orbital for the 3-membered ring, I think there are only 2 pi electrons delocalised all over the ring. The orbital ...
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Why aren't the pi electrons delocalized in cyclopropene?

I was searching on the internet whether cyclopropene is aromatic or not. I found out that the electrons are not delocalized, causing the molecule to be non-planar and so forth, a lot of reasons. But I ...
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Why total heat of hydrogenation of 1,3-cyclohexadiene is more than that of benzene?

I'm told that heat of hydrogenation (HOH) is directly proportional to number of π bonds and inversely proportional to stability. So, is the aromaticity responsible for this? Also, what is the general ...
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Is 1,2-dihydronaphthalene aromatic?

According to Hückel's rule a compound is aromatic if it has conjugation throughout the compound and the number of conjugated electrons is $4n+2$. This compound does not satisfy both: The benzene ring ...
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Why is borole not considered aromatic

I came across a problem which stated that borole isn't aromatic. I thought that borole is similar to pyrrole so it should be aromatic, but that isn't the case. Can I know why isn't it aromatic? I was ...
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Cross-conjugation and aromaticity in pyrene

I have read about non-huckel double bonds and clar's rule, but what made me confuse is that huckel's perception gives me the feeling that central bonds in polycyclic aromatic hydrocarbons (ex: pyrene) ...
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How to neutralize the stink of decomposed fish?

Recently I discovered for myself an interesting way to easily produce home made plant fertilizer that is quite effective (tested myself on the plants). It's fish emulsion (so can be used also in a ...
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Aromaticity of annulenes

Why are some annulenes such as [14] and [18]annulenes are aromatic even though they are not fully planar as cited by Wikipedia? What does it mean that they can achieve planar form?
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Clar's rule of polycyclic aromatic hydrocarbons

Clar's rule states that the Kekulé resonance structure with the largest number of disjoint aromatic π-sextets, i.e., benzene-like moieties, is the most important for characterization of properties of ...
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Is benzocyclobutadiene aromatic or anti-aromatic?

My teacher told that benzocyclobutadiene is both aromatic and anti-aromatic. I do not understand why. Can anyone explain?
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Do lone pairs contribute towards the pi electron count of heterocycles?

I'm not able to understand how the following compounds are aromatic. When should the lone pairs on heteroatoms be taken into consideration when counting the number of π electrons?
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Bond rotation energy comparison of aromatic compounds

Which of the above compounds has a lower bond rotation energy? Here is my progress: We basically need to find which compound has more single bond character. Now both compounds will break the double ...
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What explains the stability of aromatic compounds? [duplicate]

We are taught in High school that aromatic compounds are highly stable. Why is that true? Also, Why are Antiaromatic compounds highly unstable? Aromatic compounds have 4n+2 (n is a whole number) ...