Questions tagged [aromaticity]

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

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21
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3answers
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What is Y-aromaticity? Is the trinitromethanide anion aromatic?

The wikipedia article on trinitromethane claims that: There is some evidence that the anion (which obeys the $4n+2$ Hückel rule) is aromatic. Unfortunately the citation is behind a paywall so I ...
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5answers
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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 ...
14
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3answers
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Do lone pairs on substituents (e.g. in aniline) count towards Hückel's rule?

Why is aniline aromatic? Doesn't it have 8 π electrons including the lone pair on nitrogen, thereby violating Hückel's rule? The way I see it, there are 6 π electrons from the benzene ring, and an ...
22
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1answer
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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, ...
16
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2answers
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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 ...
44
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3answers
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Is buckminsterfullerene aromatic?

According to Wikipedia, The $\ce{C60}$ molecule is extremely stable,[26] withstanding high temperatures and high pressures. The exposed surface of the structure can selectively react with other ...
10
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1answer
643 views

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 ...
24
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1answer
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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. ...
19
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2answers
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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 ...
15
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2answers
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Is tropone aromatic?

Looking at resonance structure 1a, it doesn't seem that tropone is aromatic. However, the resonance structure 1b with $\ce{C+-O-}$ satisfies Hückel's rule for aromaticity. Is it correct to say that ...
12
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3answers
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Is the phenoxide ion aromatic?

Is the phenoxide ion aromatic? I read that technically it isn't aromatic because it violates some arcane rule, but I can't find any references in the literature. I don't see why it couldn't be ...
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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 ...
15
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1answer
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Is cyclopentadiene or cycloheptatriene more acidic?

Which of the following cyclic compounds are more acidic? The most acidic proton is positioned on the carbon that is at the top of the above drawings (the methylene hydrogens) on each of the two ...
8
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1answer
767 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 ...
5
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1answer
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Are the following compounds aromatic?

I know Huckel's rule states that an aromatic species must have $4n+2$ π-electrons. Is the last molecule also aromatic?
19
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1answer
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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 ...
11
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2answers
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How does a Frost diagram reproduce the solutions to the wave equation?

I came across a Frost diagram for cyclic compounds in my book, and all my book had to offer was that it geometrically reproduces the solutions of the wave equation, and can therefore determine the ...
5
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1answer
963 views

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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Why is cyclooctatetraene non planar but the cyclooctatetraenide anion planar?

I was reading some organometallics and I came upon the preparation of uranocene, $\ce{U(C8H8)2}$. It has two cyclooctatetraenide anions, $\ce{C8H8^2-}$, as ligands, with a uranium atom between them. ...
17
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2answers
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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 $\ce{N}$.
20
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1answer
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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 ...
16
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1answer
528 views

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 ...
12
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2answers
288 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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1answer
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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?
5
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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 ...
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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1answer
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Determining aromaticity of compounds [closed]

Which of the following planar structures would be aromatic? Could someone help me determining the aromaticity of the compounds? My Attempt: (i) Not an aromatic compound since it only has 4 pi ...
5
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2answers
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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, ...
3
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1answer
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Is biphenyl considered to be aromatic?

Biphenyl has 12 π-electrons and according to Hückel’s rule, it should not be aromatic because $12 \neq 4n+2$, but it nevertheless is aromatic. Why is that so?
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4answers
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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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3answers
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When do lone pairs on nitrogen contribute to aromaticity?

I've been told that 1,2,4-trimethyl-1⁠H-imidazole is aromatic. As it has four obvious pi electrons (in the double bonds), I assumed that it was anti-aromatic as opposed to aromatic. I've been ...
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-...
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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 ...
5
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3answers
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Do the π-electrons from the C=O bond in tropone contribute to Hückel 's rule?

This is a continuation of Is tropone aromatic? I'm looking at the resonance form that does have the carbonyl double-bond, 1a. Can this resonance structure also be considered aromatic? Would the ...
3
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1answer
103 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 ...
3
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0answers
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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 ...