Questions tagged [aromaticity]

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

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What is the double bond equivalence of the following compound?

What is the double bond equivalence of the given compound? The given answer is 14 (8 pi electrons and 6 rings = 14 DBE). But why isn't the lone pair on nitrogen considered?? The lone pair on nitrogen ...
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Why is quinone mono oxime more stable than 4-nitrosophenol?

When we do nitrosation of phenols, we get para-nitrosophenol as the major product, which tautomerises to quinone mono oxime. This article states that it largely exists in the quinonoid form. My ...
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Aromatic Character in Percentage?

I was just searching whether Uracil is aromatic or not and in this link$^1$ it is said that (from the abstract): High-level computational methods were tested for the enthalpy of hydrogenation of ...
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Aromaticity of Caffeine

In the Caffeine molecule, is aromaticity confined only to the 5 membered ring? The entire molecule is planar and the 6 membered ring also seems to have 6π electrons. The entire molecule has 10π ...
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Bonding in 1,4-dihydro-1,4-diborinine

In most aromatic compounds (e.g. benzene), their $\pi$-bonding molecular orbitals are completely occupied and their antibonding molecular orbitals are unoccupied. I'm wondering if there are any ...
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How is 4H‐1,4‐oxazocine aromatic?

I’ve found 4H‐1,4‐oxazocine in my chemistry book and I’m perplex as it states as aromatic: I can count 6 electrons on p orbitals which could satisfy Hückel’s $n = 1,$ but the oxygen is sp3-hybridized....
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Why is 11-oxabicyclo(4.4.1)undeca-1,3,5,7,9-pentaene aromatic?

I have been told by my instructors that for a compound to be aromatic, it must be planar. In this given molecule the oxygen seems to be out of the plane of the conjugated system: how can it still be ...
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Is azonine planar?

I came across aza[9]-annulene, which is given to be aromatic. I can clearly see it follows Hückel's rule with 8 π-electrons in the ring and the lone pair of nitrogen. But the thing that concerns me ...
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How come Cyclopropenylhydroxide exists and not cyclopropenol?

I'm currently studying aromatic compounds via online recorded lectures, and my teacher brought up about cyclopropenol and cyclopropenylhydroxide while teaching carbocylic non benzenoid compounds. He ...
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Does cyclooctatetraene also have a diradical anti-aromatic electronic state?

I read that the molecular orbital diagram of cyclobutadiene predicts that it should have a diradical nature as it has two unpaired electrons in two degenerate non bonding orbitals (one in each). Why ...
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Why aren't the pi electrons delocalized in cyclopropene?

I was searching on the internet whether cyclopropene is aromatic or not. I found out that the electrons are not delocalized, causing the molecule to be non-planar and so forth, a lot of reasons. But I ...
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Why is borole not considered aromatic

I came across a problem which stated that borole isn't aromatic. I thought that borole is similar to pyrrole so it should be aromatic, but that isn't the case. Can I know why isn't it aromatic? I was ...
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Cross-conjugation and aromaticity in pyrene

I have read about non-huckel double bonds and clar's rule, but what made me confuse is that huckel's perception gives me the feeling that central bonds in polycyclic aromatic hydrocarbons (ex: pyrene) ...
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How to neutralize the stink of decomposed fish?

Recently I discovered for myself an interesting way to easily produce home made plant fertilizer that is quite effective (tested myself on the plants). It's fish emulsion (so can be used also in a ...
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Clar's rule of polycyclic aromatic hydrocarbons

Clar's rule states that the Kekulé resonance structure with the largest number of disjoint aromatic π-sextets, i.e., benzene-like moieties, is the most important for characterization of properties of ...
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Is benzocyclobutadiene aromatic or anti-aromatic?

My teacher told that benzocyclobutadiene is both aromatic and anti-aromatic. I do not understand why. Can anyone explain?
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Bond rotation energy comparison of aromatic compounds

Which of the above compounds has a lower bond rotation energy? Here is my progress: We basically need to find which compound has more single bond character. Now both compounds will break the double ...
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What explains the stability of aromatic compounds? [duplicate]

We are taught in High school that aromatic compounds are highly stable. Why is that true? Also, Why are Antiaromatic compounds highly unstable? Aromatic compounds have 4n+2 (n is a whole number) ...
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Is this bond cleavage correct?

Is this bond cleavage of cyclopentadienone correct? The ring becomes aromatic and stability "should" increase. But my book and data from experiments suggest that the molecule isn't that polar as ...
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Confused regarding aromaticity [duplicate]

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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409 views

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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276 views

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-electron (2c-2e)...
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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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395 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 ...
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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 ...