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Questions tagged [aromaticity]

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

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Antiaromaticity can be explained by Hückel method?

Pentalene is one of the most famous antiaromatic molecules. But I obtained its energy of $\pi$ system as $8\alpha+10.46\beta$ by Hückel method (with a bit complicated but straightforward calculation). ...
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Aromaticity when lone pair atoms present [duplicate]

I am having trouble identifying aromatic compounds when elements other than carbon, like oxygen, nitrogen are present. I know the (4n+2) Huckel rule of electrons required for aromatic/anti aromatic ...
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Anti-aromatic or Non-aromatic [closed]

Please tell if the 2 given conpound are Anti-aromatic or Non-aromatic, I have confusions arising due to incosistent facts all around internet some of them are as follow : 1.) Arguments for ...
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Aromaticity fails?

Why is cyclopentadiene ($\mathrm{p}K_\mathrm{a} = 16$) less acidic than A) 2,4-pentanedione ($\mathrm{p}K_\mathrm{a} = 9$); B) phenol ($\mathrm{p}K_\mathrm{a} = 10$)? C) Even H20 (pka = 15.7) ...
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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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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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381 views

Is phosphorine (C₅H₅P) aromatic?

Phophorine seems aromatic as it has 6 conjugated electrons. But the answer given is that it is not. This seems odd since pyridine has a similar structure and is also aromatic. Thus I ask is ...
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Is the 9H-fluoren-9-ylium cation aromatic?

In this cation, there are two individual benzene rings which are aromatic. But in the entire π system, there are 12 π-electrons which should make it antiromatic. Which is correct?
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Why Isn't Huckles rule applicable to more than 3 fused rings [duplicate]

In the following compound (Pyrene) why isn't Huckle's (4n+2) rule applicable? I do know it is applicable to only mono-cyclic ring systems but what changes when there are more than 3 fused rings? ...
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Tautomerism in phenyl substituted compounds

Why doea phenyl substituted compounds have more enol content? For example, in almost all benzyl glyoxals and diarylmethanes, the enol content range up to a 100% I tried to see the effect of ...
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Is oxepin aromatic?

In my book the resonance structures drawn for oxepin include the lone pair electrons of oxygen. If we include the lone pair electrons the total number of π electrons become 8, so it should not be ...
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Why can't this molecule avoid being antiaromatic by becoming nonplanar?

The peripheral system is clearly antiaromatic if planar, but we know that antiaromatic compounds are more unstable than non aromatic compounds. So, I think that the molecule will lose its planarity ...
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How can I recognize aromatic rings in a connection table?

Given a connection table (that is, a list of atoms, their connectivities/bonds, and the type of bonds), how can I detect the presence of an aromatic ring? For reference, the aromatic rings in the ...
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240 views

Aromaticity of heterocyclic compound [closed]

This is a question of JAM 2017. According to the answer key the answer is 4. But I found only the last 3 as aromatic . So which one is the 4th aromatic compound? Please explain
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Are the following structures aromatic?

I have not seen this type of question anywhere so I do not know the answer. This is just a problem that has been roaming around in my head that I may have seen somewhere. My approach - Since ...
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Why is 5,6-dimethylidenecyclohexa-1,3-diene non-aromatic?

The compound 5,6-dimethylidenecyclohexa-1,3-diene is supposedly non-aromatic: But I have no idea why this is so. The compound is probably planar. All the atoms on the ring are $\ce{sp^2}$ hybridized. ...
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A strange case of aromaticity [duplicate]

The compound in question is given below This is one of several compounds that was listed in a JEE Advanced 2017 question about aromaticity. From the solutions it seems this compound is aromatic. ...
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Bond dissociation energy of the trihydrogen cation

Recently, in one of the questions in an assignment on the topic of energetics, we were asked to explain why the bond dissociation energy for the trihydrogen cation is much larger than what we would ...
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Why is Frost's Circle an extension of Huckel's 4n+2 rule? What physics leads to the emergent property that the circle can predict relative MOs?

The Frost Circle is a useful mnemonic to determine the relative energies for the molecular orbitals of an aromatic ring. One vertex of the polygon of the cycle is drawn pointing downwards and the ...
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How to tell whether lone pairs in heterocycles contribute to aromaticity? [duplicate]

How can I decide whether lone pair electrons take part in the continuous overlap of electron or not? For example, the lone pair in pyridine is not a part of the conjugated system, whereas the lone ...
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1answer
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Aromaticity of two rings connected by double bond

I want to know how to decide aromaticity of two rings connected by a double bond. For example consider the ring in which when double bond is broken generates tropylium cation and cyclopentadienyl ...
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Can Hückel's rule be applied to inorganic compounds?

Hückel's rule helps us know which molecular orbital, bonding or antibonding contains more electrons, and it is derived from the same. And on the basis of this, we can find out the stability of the ...
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Is cyclononatetraenylium antiaromatic?

I was thinking that it might be non aromatic since the ring is very big and it might bend just like COT (cyclo-octatetraene) does to avoid destabilization due to antiaromaticity but I don't know if ...
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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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Rank the following radicals in order of decreasing stability

Question Rank the following radicals in order of decreasing stability Aromaticity makes a cyclic compund more stable. Here, 1 and 3 are aromatic since they follow Huckels rule(Or am I wrong ...
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The order of aromaticity of benzene, thiophene, pyrrole, furan, and pyridine

I have been taught that the order of aromaticity is: benzene > thiophene > pyrrole > furan. However, I have been unable to deduce any logical explanation for that order. Also, I wish to compare ...
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Is borazine aromatic?

I came across this structure which has got pi bonds only in its canonical forms (which are also unstable compared to the Ist structure), is it aromatic? Also, is it compulsory for an aromatic ...
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Deciding the aromaticity of two napthalene-like rings [duplicate]

Why is the first compound aromatic and the second compound non-aromatic? In the first compound, the left side of the ring is aromatic but the right side isn't. Second compound satisfies all the ...
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Directionality of ring current-induced magnetic fields in purines

What would be the directions of ring current-induced magnetic fields in purine-like heterocycles in a ​strong magnetic field? Would be the antiparallel state be a default state for these substances in ...
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1answer
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Is azirene an antiaromatic compound

I believe that a compound which is planar and having parallel p orbital with $4n\,\pi$ electrons is antiaromatic, but azirene has a lone pair in a $\text{sp}^3$ hybrid orbital. Shouldn't it be non-...
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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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What is three dimensional aromaticity?

I have recently come across a statement which states: The relative stability of the 1,3-dehydro-5,7-adamantanediyl dication is ascribed to its three-dimensional aromaticity. [1] My ...
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Why is the cyclopropenium ion aromatic?

I don't understand how the 'cyclopropenium' ion is aromatic. According to my understanding, the carbons within the central 3 carbon ring must each be sp2 hybridised with a single electron in a p ...
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Loss of aromaticity vs low entropy of activation

Even if reaction has low entropy of formation does that mean it is favorable to loss aromaticity and form highly strained cyclopropane ring? Why this reaction happens? Maybe someone can explain that ...
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Resonance in benzenylium cation [duplicate]

Why is this type of resonance not possible? My book says that the positive charge is localised, and resonance is not possible. But I have drawn the resonance structures (though you can note that the ...
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1answer
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Is 2a¹H-cyclopenta[cd]indene aromatic?

In this question, 2a1H-cyclopenta[cd]indene is said to be aromatic. My doubt is that the central C atom (connecting the three cyclic rings) is sp³ hybridized. So I think it should be non planar thus ...
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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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Why is triptycene aromatic?

I came across this wonderful compound, triptycene. Why is triptycene an aromatic compound, even though it is non-planar? I thought planarity was a requirement for aromaticity.
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Is the triplet state of the cyclopentadienyl cation really aromatic?

While checking the ASAP articles of the Journal of the American Chemical Society I came across a very interesting contribution by Costa et al. who synthesised a $\ce{BF3}$ stabilised cyclopentadienyl ...
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How does the cyclopropyl group influence conjugation and aromaticity?

While answering the question Why isn't cyclobutane planar?, I recollected that cyclopropane and its derivatives behave like double-bond compounds, e.g. a cyclopropyl group can potentially be ...
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Why do dithiins have 8 π-electrons?

It is mentioned on Wikipedia that dithiins have 8 π-electrons. Why is this so? I was thinking it would suffice for just one of the lone pairs on one of the sulfur atoms to participate in resonance ...
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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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Is the middle ring of this organic compound aromatic?

Is the middle ring with 5 atoms of (4⁠Z)-4-[(4-methoxyphenyl)methylidene]-5-methyl-2-phenyl-2,4-dihydro-3⁠H-pyrazol-3-one aromatic? The carbonyl group could become a negatively charged oxygen, the ...
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1answer
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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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1answer
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Is cyanidin aromatic?

The structure of cyanidin is as follows: There are eight double bonds in the entire compound, and hence $8 \times 2 = 16$ π-electrons, which does not satisfy the $4n + 2$ rule. However, the molecule ...
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Cyclobutadiene - Jahn–Teller effect or not?

In transition metal chemistry the Jahn–Teller effect arises when the configuration of the metal ion and d orbital splitting set up a doubly degenerate state, which is less stable than a state without ...
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Why is 1H-borepine aromatic?

For a compound to be aromatic, each atom in the ring must be a part of conjugation. Boron here has no lone pair, so how can 1⁠H-borepine be aromatic as I was told by someone?
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What are modern approaches to describe and/or quantify aromaticity?

I know that Schleyer described an approach for evaluating aromaticity using nucleus-independent chemical shifts (NICS, see e.g. Chem. Rev. 2005, 105 (10), 3842–3888) quite some time back. I also ...
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Is a compound aromatic if it also has anti-aromatic rings?

Is 5,6,11,12-tetradehydrodibenzo[a,e][8]annulene aromatic? If I use Hückel's rule for the whole molecule, I get the answer as anti-aromatic. But the compound has two benzene rings which are ...
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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.