Questions tagged [aromaticity]

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

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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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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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Aromatic or non aromatic compound [duplicate]

I am providing a picture of an organic compound , according to me the compound should be non aromatic as it has sp3 hybridized carbon in other ring , but in NCERT textbook it is written the given ...
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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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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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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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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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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 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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What is the justification for Hückel's rule?

I know that experimentally, the rule has been verified but I am having trouble understanding why it works. I see no reason why equivalent cyclic structures can undergo resonance and be just as stable. ...
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Are graphite and hexagonal boron nitride aromatic

Are graphite and hexagonal boron nitride aromatic? Graphite has a planar network of 6-membered rings with each carbon connected to three other carbons. Since the valency of carbon is not satisfied, ...
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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 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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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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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 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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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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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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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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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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Is a pyrylium ring aromatic?

I am trying to figure out which rings in callistephin are aromatic: I know that the benzene rings definitely are aromatic, but I'm not sure about the ring with the positively charged oxygen (...
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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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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 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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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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Is this sydnone aromatic?

Is the following molecule aromatic? It does seem like it will be aromatic because it is similar to furan. I am confused because of the positive charge on the $\ce{N}$.
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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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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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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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Why is only one lone pair in imidazole delocalised?

I was wondering why only one of the nitrogen lone pairs in imidazole is involved in the delocalized π-system. Specifically, I was wondering why it is that lone pair B in particular is delocalized, ...
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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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Why is cyclopentadiene anion is aromatic but cycloheptatrienyl anion is not?

I just can't seem to figure this out. The cyclopentadienyl anion (1) is aromatic, but the cycloheptatrienyl anion (2) is not, though its cation (3) is. Why?
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Is cyclobutadiene antiaromatic?

Cyclobutadiene is very unstable. But, some sources claim that this instability can be attributed to other factors such as ring and angle strain rather than antiaromaticity. According to some, ...
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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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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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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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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 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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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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Is a quinone ring aromatic?

I'm trying to work out which are the aromatic ring systems in the drug aklavinone: I am trying to follow Hückel's rules that the compound must be cyclic, be planar, possess a p-orbital on every atom ...
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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. ...