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26 votes
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Is [7]сirculene aromatic or anti-aromatic?

TL;DR: We don't count π electrons here, rather the π conjugated circuits [1]. [7]-сirculene has all conjugated circles of size $4n + 2,$ and none of $2n,$ what makes it an aromatic compound. Strictly ...
andselisk's user avatar
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24 votes
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Cyclobutadiene - Jahn–Teller effect or not?

Very interesting question, and it kept me up despite daylight saving time cheating me of one hour of sleep last night... A good reference is Albright, Burdett and Whangbo, Orbital Interactions in ...
orthocresol's user avatar
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23 votes
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Is borazine aromatic?

The modern definition of aromaticity from deep theoreticians is that the π-system needs to support aromatic ring currents. Borazine can support it, so it is technically aromatic. Aromatic systems ...
permeakra's user avatar
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22 votes
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Are graphite and hexagonal boron nitride aromatic

Graphite is definitely aromatic and boron nitride is at least partially aromatic. For instance, in this paper, the authors calculate the percent resonance energy (%RE) of graphite as a comparison to ...
jheindel's user avatar
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22 votes
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Is a compound aromatic if it also has anti-aromatic rings?

The molecule actually optimizes to a planar, delocalized $\pi$ system Using B3LYP/6-31G(d) optimizations, we see that the molecule optimizes to become planar. (The initial configuration was ...
Geoff Hutchison's user avatar
21 votes
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Why is 1H-borepine aromatic?

1H-borepine is isoelectronic to the cycloheptatrienyl cation. In both cases, you have a planar ring of seven atoms, whose hybridisation is close enough to $\mathrm{sp^2}$ to allow for a third p-...
Jan's user avatar
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19 votes
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Is biphenyl considered to be aromatic?

The two rings in biphenyl are inclined at an angle of 44° to each other because of the large steric repulsion between the ortho hydrogens on each ring. For Hückel's rule to be applied, the molecule ...
bon's user avatar
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17 votes
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Is the cyclopropenyl anion antiaromatic?

When you have a ring that has $4n$ π electrons it's anti-aromatic if you force it into a fully conjugated cycle. Often such rings find a way to break the unfavorable (or at least, less favored) anti-...
Oscar Lanzi's user avatar
16 votes

Applying Huckel's rule to non-planar compounds

Number 2 is not aromatic because transannular $\ce{C-H}$ interactions cause the molecule to be non-planar although it satisfies $4n+2$. This problem was solved by the synthesis of number 4, which, ...
user55119's user avatar
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16 votes
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Is oxepin aromatic?

Oxepin is certainly not aromatic. If it were flat and the oxygen atom was sp2 hybridized, then it would be an 8π-electron anti-aromatic system, but to avoid being anti-aromatic, it exists in a boat-...
Organic Chemistry Explained's user avatar
16 votes
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What is quasi-aromaticity?

In general, we can describe a quasi aromatic compound as a compound, which is ionic in nature with a counter ion, and the $\pi$ electrons in such compounds follow Huckel's rule ($4n+2$). In other ...
Mathew Mahindaratne's user avatar
15 votes
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Is the triplet state of the cyclopentadienyl cation really aromatic?

TL;DR Yes. For cyclic conjugated systems in the $T_1$ state (i.e. lowest energy triplet excited state), $4n$ electrons means aromatic and $4n+2$ means anti-aromatic. The $T_1$ state of the ...
orthocresol's user avatar
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15 votes
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Why is triptycene aromatic?

The confusion arises because of a simplistic definition of aromaticity. What matters for aromaticity is the planarity of the relevant part of the molecule. In triptycene there are three planar ...
matt_black's user avatar
15 votes
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Can Hückel's rule be applied to inorganic compounds?

Huckel's rule can be applied to "inorganic" cyclic molecules but only if they have a delocalised pi system. They also have to have flat (or close to flat) rings. Recently some N5 rings which 6 pi ...
Nuclear Chemist's user avatar
14 votes

The order of aromaticity of benzene, thiophene, pyrrole, furan, and pyridine

The main criteria of aromaticity is resonant or delocalization energy. It is difference between energy contained in bonds if they were localized like in Kekule's formula for benzene and actual energy. ...
Eldar's user avatar
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14 votes
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Why is borole not considered aromatic

A very basic way to do this would be to draw a diagram that shows the p-orbitals going above and below the plane. For Borole, the bonding orbitals would look like as shown below (taken from the ...
Safdar Faisal's user avatar
13 votes
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Is 1,2-dihydronaphthalene aromatic?

Hückel's rules are a very concise set of very strict rules. Most aromatic compounds do not comply with these. Hückel (4n + 2) rule Monocyclic planar (or almost planar) systems of ...
Martin - マーチン's user avatar
12 votes
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Is phosphorine (C₅H₅P) aromatic?

Phosphorine (IUPAC: phosphinine) actually has aromatic character nearly as great (88%) as that of benzene. According to the reference, phosphorine is sufficiently stable to be handled without air-...
Oscar Lanzi's user avatar
12 votes

Are there any aromatic systems that don't contain any rings?

The word "aromatic" is most commonly used for systems that do have rings, but an enhanced resonance stabilization with delocalized $\pi$ bonding can occur without rings whether we apply the ...
Oscar Lanzi's user avatar
12 votes
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Do aromatic canonical structures make the overall compound aromatic?

Not always. Consider, for example, 4-pyrone. It is possible to draw canonical structures containing the pyrylium heterocycle, which is aromatic. However, the contribution of this aromatic resonance ...
Nicolau Saker Neto's user avatar
11 votes

Is cycloheptatriene aromatic or not?

You are correct. The conjugation does not extend all the way around the ring, so the molecule is not aromatic. In addition, the single methylene group ($\ce{CH2}$) sticks out of the plane of the rest ...
f'''s user avatar
  • 380
11 votes

Are graphite and hexagonal boron nitride aromatic

Yes, both graphite and borazine are aromatic in nature as each ring of a plane have six π-electrons (similar to benzene). This aromaticity explains why graphite and borazine are unusually ...
Swastik's user avatar
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11 votes

Why is triptycene aromatic?

First of all, there's one thing you must know, aromaticity is a property of a ring system and not always of the molecule. Small molecules like benzene and pyridine have only one ring, so it's "ok" ...
Pritt says Reinstate Monica's user avatar
11 votes
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Aromaticity of 1,4-Dioxin

Aromaticity is a fuzzy subject and there are no strict mathematical rules. There is no recognised unilateral theory that does explain it. This becomes a real issue when we are dealing with compounds ...
Martin - マーチン's user avatar
11 votes
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Are 2-pyridone and cycloheptatrienide antiaromatic?

This can be confusing, especially when you are given a molecule that has a pendant carbonyl oxygen like your first molecule. Strictly speaking, the $4n+2$ and $4n$ electron rules apply only when the ...
Oscar Lanzi's user avatar
10 votes
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Reaction of cyclooctatetraene with sulfuric acid

This is a rather unusual and interesting case of aromaticity, which has been given a special name: homoaromaticity. The Wikipedia page does a quite nice job of explaining what's going on. As you state,...
Nicolau Saker Neto's user avatar
9 votes

Is tropone aromatic?

The best answer to this theme is probably given by Barach in his book BACHRACH, Steven M. Computational organic chemistry. Annual Reports Section" B"(Organic Chemistry), 2008, 104: 394-426. ...
Jojostack's user avatar
  • 573
9 votes

Is benzocyclobutadiene aromatic or anti-aromatic?

Benzocyclobutadiene has an aromatic benzene ring as well as an anti-aromatic cyclobutadiene ring. This gives it the characteristics of both aromatic and anti-aromatic compounds. Now, according to ...
Safdar Faisal's user avatar
9 votes

Why is borole not considered aromatic

Simply for the beginners in organic chemistry, this explanation of aromaticity is good enough: An aromatic (or aryl) compound contains a set of covalently bound atoms with specific characteristics: ...
Mathew Mahindaratne's user avatar
9 votes

why is benzene ring ubiquitous in almost all the organic compounds

By "benzene ring", I assume that you mean the aryl functional group: $\hspace{8 cm}$ Molecules with the above motif - called arenes - are common throughout nature and are present in a ...
sharpbencil's user avatar

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