Questions tagged [aromaticity]
For questions about the concept of aromaticity. Do not use for reactions of aromatic compounds.
3
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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 ...
7
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1answer
120 views
What is quasi-aromaticity?
While studying about aromaticity I came through this topic of quasi-aromaticity. Can you please tell me what it actually is?
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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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1answer
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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 ...
3
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0answers
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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 ...
8
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0answers
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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-...
2
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1answer
44 views
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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1answer
19 views
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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1answer
38 views
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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0answers
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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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1answer
409 views
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 ...
0
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1answer
77 views
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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2answers
335 views
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 ...
0
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2answers
80 views
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 ...
11
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1answer
394 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 ...
7
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0answers
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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?
...
4
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1answer
775 views
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 ...
5
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2answers
112 views
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 ...
5
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1answer
114 views
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 ...
1
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1answer
290 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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1answer
242 views
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 ...
5
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1answer
153 views
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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1answer
125 views
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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2
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0answers
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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 ...
3
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1answer
129 views
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 ...
4
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1answer
356 views
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 ...
5
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1answer
334 views
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 ...
13
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3answers
467 views
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 ...
11
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1answer
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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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1answer
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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 ...
4
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1answer
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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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3answers
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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 ...
16
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2answers
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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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0answers
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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 ...
17
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1answer
189 views
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
226 views
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-...
4
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1answer
176 views
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?
18
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1answer
429 views
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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4answers
666 views
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 ...
6
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1answer
114 views
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 ...
0
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0answers
42 views
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 ...
5
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1answer
318 views
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 ...
8
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1answer
699 views
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 ...
12
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2answers
273 views
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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2answers
693 views
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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0answers
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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 ...
6
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2answers
257 views
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 ...
