Aromaticity explain by Hückel's Rule and Craig's Rule for UGC CSIR-NET GATE IIT JAM TIFR DRDO BARC Chemistry.
Application of Aromatic, Nonaromatic, Antiaromatic, Homoaromaticity & Quasi-aromatic compounds for competitive examination.
Application of Aromaticity with PDF file.
Basic Concepts
of Aromaticity //
📚 PDF File also available 👉👉 Click Here
Order Stability and Resonance Energy:- Aromatic > Homoaromatic > Antiaromatic > Nonaromatic
📚👉👉 PDF of Aromaticity || Study Material of Career Endeavor
Full tutorial , click here👇👇
Aromaticity explain by Craig's rule
📚 PDF File also available 👉👉 Click Here
Order Stability and Resonance Energy:- Aromatic > Homoaromatic > Antiaromatic > Nonaromatic
Application of Aromatic, Nonaromatic, Antiaromatic, Homoaromaticity & Quasi-aromatic compounds for competitive examination.
Application of Aromaticity with PDF file.
Basic Concepts
of Aromaticity //
Aromatic, Nonaromatic, Antiaromatic compounds.
Quasi-aromatic & homoaromaticity.
Quasi-aromatic & homoaromaticity.
Aromaticity Based on Hückel's Rule.
Application of Aromaticity.
📚 PDF File also available 👉👉 Click Here
Order Stability and Resonance Energy:- Aromatic > Homoaromatic > Antiaromatic > Nonaromatic
Aromaticity:- in Organic Chemistry, the Aromaticity is a property of Cyclic, planar structure with a ring of resonance bonds that gives the increased stability compared to other geometric with the same set of atoms. Aromatic compounds are very stable, and they do not break apart easily to react with other compounds.
Antiaromatic:- it is also a Cyclic molecule with a pi-electron system but there has higher energy due to the presence of 4n delocalized electrons in it. And Antiaromatic compounds are highly
unstable and highly reactive in nature.
Nonaromatic:- nonaromatic are every other molecules that fails one of these conditions (i.e., Cyclic, planar, conjugation and 4n or (4n+2) number of delocalized electrons, so anyone of these conditions is not fulfill, then the molecule is called non Aromatic compound).
Quasi-aromatic:- Quasi-aromatic compounds are those in which the charges are present on the ring/molecule, and they take a part of Aromaticity of the compound.
Homoaromaticity:- in Organic Chemistry, it refers to a special type of Aromaticity in which conjugation is interrupted by a single sp³ hybridized carbon atom.
Antiaromatic:- it is also a Cyclic molecule with a pi-electron system but there has higher energy due to the presence of 4n delocalized electrons in it. And Antiaromatic compounds are highly
unstable and highly reactive in nature.
Nonaromatic:- nonaromatic are every other molecules that fails one of these conditions (i.e., Cyclic, planar, conjugation and 4n or (4n+2) number of delocalized electrons, so anyone of these conditions is not fulfill, then the molecule is called non Aromatic compound).
Note:- "All Quasi-aromatic compounds are aromatic but all aromatic compounds are not Quasi-aromatic compounds"
Quasi-aromatic:- Quasi-aromatic compounds are those in which the charges are present on the ring/molecule, and they take a part of Aromaticity of the compound.
Homoaromaticity:- in Organic Chemistry, it refers to a special type of Aromaticity in which conjugation is interrupted by a single sp³ hybridized carbon atom.
Hückel's Rule for Aromaticity:- In 1931, German chemist and physicist Erich Hückel proposed a theory to determine if a planar ring molecule would have Aromatic properties. His rule states that if a Cyclic, planar molecules has (4n+2) number of π electrons, then it is considered as an Aromatic compound. This rule come to be known as Hückel's Rule for Aromaticity.
Four Criteria for Aromaticity:- When we deciding a compound is Aromatic, then go through the following criteria. If the compound doesn't meet all the following four criteria , then it is called not Aromatic compound.
1. The molecule should be Cyclic.
2. The molecule should be planar.
3. The molecule should be maintain conjugation.
4. The molecule has (4n+2)π number of electrons. (n= 0, 1,2,3....)
📚✔️ In the given molecule Pyrene , the π bond shown in green is in cross conjugation (shown in green in figure 1). This bond( figure 2) is excluded from interaction with rest of conjugated system. Hence , the central C=C isn't hosted by the largest p orbital loop, so it's not counted towards Hückel's rule for aromaticity.
The outer periphery (shown in blue in figure 3), is a loop of 14π electrons , therefore aromatic. This may be possible hückel double bond you are referring to.
The π bond in cross-conjugation (shown in green) maybe non-hückel double bond.
Four Criteria for Aromaticity:- When we deciding a compound is Aromatic, then go through the following criteria. If the compound doesn't meet all the following four criteria , then it is called not Aromatic compound.
1. The molecule should be Cyclic.
2. The molecule should be planar.
3. The molecule should be maintain conjugation.
4. The molecule has (4n+2)π number of electrons. (n= 0, 1,2,3....)
📚✔️ In the given molecule Pyrene , the π bond shown in green is in cross conjugation (shown in green in figure 1). This bond( figure 2) is excluded from interaction with rest of conjugated system. Hence , the central C=C isn't hosted by the largest p orbital loop, so it's not counted towards Hückel's rule for aromaticity.
The outer periphery (shown in blue in figure 3), is a loop of 14π electrons , therefore aromatic. This may be possible hückel double bond you are referring to.
The π bond in cross-conjugation (shown in green) maybe non-hückel double bond.
📚👉👉 PDF of Aromaticity || Study Material of Career Endeavor
Order Stability and Resonance Energy:-
Aromatic > Homoaromatic > Antiaromatic > Nonaromatic
Aromatic > Homoaromatic > Antiaromatic > Nonaromatic
Full tutorial , click here👇👇
Aromaticity explain by Craig's rule
📚 PDF File also available 👉👉 Click Here
Order Stability and Resonance Energy:- Aromatic > Homoaromatic > Antiaromatic > Nonaromatic
Aromaticity:- in Organic Chemistry, the Aromaticity is a property of Cyclic, planar structure with a ring of resonance bonds that gives the increased stability compared to other geometric with the same set of atoms. Aromatic compounds are very stable, and they do not break apart easily to react with other compounds.
Antiaromatic:- it is also a Cyclic molecule with a pi-electron system but there has higher energy due to the presence of 4n delocalized electrons in it. And Antiaromatic compounds are highly unstable and highly reactive in nature.
Nonaromatic:- nonaromatic are every other molecules that fails one of these conditions (i.e., Cyclic, planar, conjugation and 4n or (4n+2) number of delocalized electrons, so anyone of these conditions is not fulfill, then the molecule is called non Aromatic compound).
Quasi-aromatic:- Quasi-aromatic compounds are those in which the charges are present on the ring/molecule, and they take a part of Aromaticity of the compound.
Homoaromaticity:- in Organic Chemistry, it refers to a special type of Aromaticity in which conjugation is interrupted by a single sp³ hybridized carbon atom.
Largest molecular wheel ever made pushes limits of aromaticity rules :-
Published:- Royal Society of Chemistry
BY MICHAEL GROSS, 22 JANUARY 2020
Source:- Royal Society of Chemistry (RSC)
Reference:- Global Aromaticity at the Nanoscale; Nature Chemistry (2020)
Source:- Chemistry World
Hückel’s rule, it is developed for the explanation of the properties of the six aromatic electrons in benzene, and it is still valid for a giant aromatic ring with 162 π electrons that is many times the size of the simplest aromatic.
E. Hückel developed his quantum theory of molecular orbitals in 1931. One consequence of his calculations was that rings with alternating single and double bonds and 4n+2 π electrons should be aromatic like benzene. Later work described those with a number divisible by four, like cyclobutadiene, as anti-aromatic.
In chemical terms, the aromatic rings are strongly stabilised, while the anti-aromatics are destabilised and it is less commonly encountered. A physical measure to check if a molecule is one or the other is the ring current induced when the molecule is exposed to a magnetic field such as during nuclear magnetic resonance spectroscopy. In aromatics, the current will oppose the external magnetic field within the ring, while in the anti-aromatics it will coincide with it.
Over the decades, there are many aromatic and anti-aromatic molecules have been synthesised, and all obeyed Hückel’s simple rule. Porphyrins, for instance, the macrocycles found in haemoglobin and chlorophyll, provide a natural example with 18 π electrons. It remained unclear, however, how large aromatic rings can get before Hückel’s rule collapses.
Three years ago, Harry Anderson’s group at the University of Oxford, UK, constructed the world’s largest aromatic ring with a total of 78 π electrons. The molecular wheel was made up of six porphyrin rings grouped around a benzene hub, with six spokes connecting to zinc ions complexed by the porphyrins
Wheel chemistry Now, the chemists have broken their own record with a giant aromatic wheel containing a grand total of 162 π electrons. Doubling the size of their previous record holder, they constructed the wheel’s rim out of 12 porphyrin rings, put two stacked benzene hubs in the middle and created 12 longer spokes.
They also combined two halves of the smaller wheel with four spokes each to form an elongated construct with eight porphyrins. All in all, the researchers produced eight different nanorings in various oxidation states, accounting for 24 different molecular species. In all cases where ring currents could be detected, they were in accordance with Hückel’s rule. ‘It is amazing that the simple Hückel 4n+2 rule predicts the aromaticity or anti-aromaticity of a molecule better than sophisticated density functional theory calculations,’ Anderson tells Chemistry World.
The porphyrin constructs readily accept or release electrons, which enabled the researchers to study aromatic and anti-aromatic states using the same molecular structure. The different redox states can be distinguished by NMR, even when they are present in the same solution. Thus the system provides a convenient switch and readout for its aromatic properties. The group added a further twist to the tale when they combined the large 12-porphyrin cycle with two smaller hub-and-spoke molecules. As they had hoped, the ring wrapped itself into a figure-of-eight to accommodate both hub complexes. As the two parts of the ring now run in opposite directions, theory had predicted that the ring currents cancel out – a phenomenon the group was now able to observe for the first time. ‘The size of our nanoring makes it possible to achieve the required geometry for current cancellation,’ Anderson explains. This allowed the researchers to use geometry and redox state as independent switches to manipulate the aromatic properties of nanorings.
Rainer Herges from the University of Kiel, Germany, praised the advance into the terra incognita between classical and quantised electromagnetic systems, commenting: ‘The first results are already unexpected and surprising. I am sure the exploration of the field will unravel further fascinating effects and applications such as quantum computing.’ Meanwhile, the upper limit of Hückel’s rule remains to be found.
Source :- Royal Society of Chemistry
Reference:- M D Peeks, T D W Claridge and H L Anderson, Nature, 2017,
Reference:- Nature Chemistry (2020)
Antiaromatic:- it is also a Cyclic molecule with a pi-electron system but there has higher energy due to the presence of 4n delocalized electrons in it. And Antiaromatic compounds are highly unstable and highly reactive in nature.
Nonaromatic:- nonaromatic are every other molecules that fails one of these conditions (i.e., Cyclic, planar, conjugation and 4n or (4n+2) number of delocalized electrons, so anyone of these conditions is not fulfill, then the molecule is called non Aromatic compound).
Quasi-aromatic:- Quasi-aromatic compounds are those in which the charges are present on the ring/molecule, and they take a part of Aromaticity of the compound.
Homoaromaticity:- in Organic Chemistry, it refers to a special type of Aromaticity in which conjugation is interrupted by a single sp³ hybridized carbon atom.
Largest molecular wheel ever made pushes limits of aromaticity rules :-
Published:- Royal Society of Chemistry
BY MICHAEL GROSS, 22 JANUARY 2020
Source:- Royal Society of Chemistry (RSC)
Reference:- Global Aromaticity at the Nanoscale; Nature Chemistry (2020)
Source:- Chemistry World
 |
| Giant Aromatic Ring |
Hückel’s rule, it is developed for the explanation of the properties of the six aromatic electrons in benzene, and it is still valid for a giant aromatic ring with 162 π electrons that is many times the size of the simplest aromatic.
E. Hückel developed his quantum theory of molecular orbitals in 1931. One consequence of his calculations was that rings with alternating single and double bonds and 4n+2 π electrons should be aromatic like benzene. Later work described those with a number divisible by four, like cyclobutadiene, as anti-aromatic.
In chemical terms, the aromatic rings are strongly stabilised, while the anti-aromatics are destabilised and it is less commonly encountered. A physical measure to check if a molecule is one or the other is the ring current induced when the molecule is exposed to a magnetic field such as during nuclear magnetic resonance spectroscopy. In aromatics, the current will oppose the external magnetic field within the ring, while in the anti-aromatics it will coincide with it.
Over the decades, there are many aromatic and anti-aromatic molecules have been synthesised, and all obeyed Hückel’s simple rule. Porphyrins, for instance, the macrocycles found in haemoglobin and chlorophyll, provide a natural example with 18 π electrons. It remained unclear, however, how large aromatic rings can get before Hückel’s rule collapses.
Three years ago, Harry Anderson’s group at the University of Oxford, UK, constructed the world’s largest aromatic ring with a total of 78 π electrons. The molecular wheel was made up of six porphyrin rings grouped around a benzene hub, with six spokes connecting to zinc ions complexed by the porphyrins
 |
| Largest Molecular Wheel |
Wheel chemistry Now, the chemists have broken their own record with a giant aromatic wheel containing a grand total of 162 π electrons. Doubling the size of their previous record holder, they constructed the wheel’s rim out of 12 porphyrin rings, put two stacked benzene hubs in the middle and created 12 longer spokes.
They also combined two halves of the smaller wheel with four spokes each to form an elongated construct with eight porphyrins. All in all, the researchers produced eight different nanorings in various oxidation states, accounting for 24 different molecular species. In all cases where ring currents could be detected, they were in accordance with Hückel’s rule. ‘It is amazing that the simple Hückel 4n+2 rule predicts the aromaticity or anti-aromaticity of a molecule better than sophisticated density functional theory calculations,’ Anderson tells Chemistry World.
The porphyrin constructs readily accept or release electrons, which enabled the researchers to study aromatic and anti-aromatic states using the same molecular structure. The different redox states can be distinguished by NMR, even when they are present in the same solution. Thus the system provides a convenient switch and readout for its aromatic properties. The group added a further twist to the tale when they combined the large 12-porphyrin cycle with two smaller hub-and-spoke molecules. As they had hoped, the ring wrapped itself into a figure-of-eight to accommodate both hub complexes. As the two parts of the ring now run in opposite directions, theory had predicted that the ring currents cancel out – a phenomenon the group was now able to observe for the first time. ‘The size of our nanoring makes it possible to achieve the required geometry for current cancellation,’ Anderson explains. This allowed the researchers to use geometry and redox state as independent switches to manipulate the aromatic properties of nanorings.
Rainer Herges from the University of Kiel, Germany, praised the advance into the terra incognita between classical and quantised electromagnetic systems, commenting: ‘The first results are already unexpected and surprising. I am sure the exploration of the field will unravel further fascinating effects and applications such as quantum computing.’ Meanwhile, the upper limit of Hückel’s rule remains to be found.
Source :- Royal Society of Chemistry
Reference:- M D Peeks, T D W Claridge and H L Anderson, Nature, 2017,
Reference:- Nature Chemistry (2020)
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