Questions tagged [aromaticity]

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

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Confused regarding aromaticity

I can understand the aromaticity in the second but can't in the first structure. The second structure is aromatic since it has a continuous conjugation in the rings, but the first structure has no ...
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How does actually negative charge travel in phenol from ortho to para to ortho? [duplicate]

When we say negative charge flows from ortho to para position, and electron density at ortho and para is more, where does electron actually stay at ortho and para? Is it at $p_\mathrm{z}$ orbital or ...
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Why aren't all bonds in cyclobutadiene not equal? [duplicate]

Cyclobutadiene is like benzene in that it has alternating single and double bonds in a ring. However, it's bonds are not the same length, the double bonds being shorter than single bonds. The molecule ...
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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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Is the following molecule aromatic or antiaromatic?

This molecule has the same chemical formula $\ce{C20H10}$ as corannulene (which also is non-planar) and corannulene is aromatic, so I'm pretty sure that this molecule should be aromatic too. I tried ...
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Cycloheptatrienyl carbanion aromaticity

Many sources including previous answers on Stack Exchange claim that it is antiaromatic. But in a different yet similar question, I have also seen people saying that a monocyclic ring with 7 or more ...
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Why does cyclobutadieneiron tricarbonyl behave aromatically?

It is said that $\ce{(\eta^4-C4H4)Fe(CO)3}$ can undergo electrophilic substitution reactions. Therefore, it displays aromaticity. For the iron atom, it has $8$ electrons in its outer shell initially ...
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What is the Criteria for a Compound Being Non-aromatic vs. Anti-aromatic?

Anti-aromatic compounds are formed with a cyclic system of planar, overlapping p orbitals containing a non-Huckel number of electrons (i.e. not 4n+2 electrons -n being a natural number-). Non-aromatic ...
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Is cyclo[18]carbon aromatic?

How does this compound even exist? Having such a massive ring strain. Is it even conjugated? As it's resonance structure will have all double bonds. Since it was reported to be found, there must be ...
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Why adenine is an aromatic molecule? [duplicate]

Why is this molecule aromatic? If we include the two π-electrons of the nitrogen on the top $(\ce{NH2})$ the number of π-electrons would be 12, thus it can’t be aromatic.
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What is non-hückel double bond of Aromaticity? [duplicate]

Chemistry of Aromaticity. What's non hückel double bond ? What are the difference between hückel and non-hückel double bond ? [ Here, in figure the green one is non hückel double bond ]
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Is black phosphorous aromatic?

I know that graphite and boron nitride are aromatic in nature. In a similar way, can black phosphorous too exhibit aromaticity? Since it is essentially the same having 6 membered rings with lone ...
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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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What is jellium aromaticity?

As I understand, if a molecule is cyclic and planar, then every atom in the ring must be $\ce{sp^2}$-hybridized and the molecule must have [4n+2] π electrons, where n∈N (Hückel’s rule). An article in ...
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Consequences of ortho effect on resonance

Consider any carboxylic acid with any group at ortho position. According to ortho effect, the resonance of the $\ce{C=O}$ with the ring is inhibited. Is this resonance entirely lost? Or some little ...
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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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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-...
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Why is adenine aromatic?

I don't think it follows the $4n + 2$ rule. The double bonds give 8 π electrons. Then the lone pairs on the $\ce{NH}$ and $\ce{NH2}$ groups are delocalized (are they?) so they must contribute 4 π ...
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Aromaticity of Tropone [duplicate]

When we are determining if a given compound is aromatic using Hückel's rule, we count the number of delocalized $\pi$ electrons. In tropone for example, if I wanted to count the number of delocalized ...
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Partial Aromaticity and Anti-aromaticity [closed]

The following resonance structures are possible for the given compound. (a) promotes both aromaticity and Anti-aromaticity whereas (b) promotes aromaticity. In the resonance hybrid, (b) contributes ...
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Resonance in a non-planar molecule

I am well aware that the following compound is non-planar and hence, will not be anti-aromatic but non-aromatic. But I wonder whether resonance will occur to some extent i.e. whether any three ...
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Understanding Aromaticity

I was just doing a simple question and for no reason, I drew the resonating structures of the compound as shown. I can see that some of the resonating structures seem to be aromatic while others seem ...
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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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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) water $(\mathrm{p}K_\mathrm{a}...
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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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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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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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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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1answer
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Are p‐xylylene and fulvene aromatic?

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 ...
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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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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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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-...