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Anti-aromatic and Non-aromatic compounds

Is the cyclopropenyl anion antiaromatic?Why is cyclopentadiene anion is aromatic but cycloheptatrienyl anion is not?Determining aromaticity of compoundsWhat is Y-aromaticity? Is the trinitromethanide anion aromatic?Is the cyclopropenyl anion antiaromatic?Is the triplet state of the cyclopentadienyl cation really aromatic?Is borazine aromatic?Is an antiaromatic compound more stable than a non-aromatic compound because of more conjugation?Do there exist aromatic compounds similar to azulene?Aromaticity of two rings connected by double bondWhat are the different types of catalysts used in catalytic hydrogenation of alkynes?Why can't this molecule avoid being antiaromatic by becoming nonplanar?

2

$begingroup$

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 Cyclopropenyl Anion

a.) Wikipedia which under the heading of "Effects on reactivity"
clearly states that :

"However, the cyclopropenyl anion has 4 π electrons in a cyclic system
and in fact has a substantially higher pKa than 1-propene because it
is antiaromatic and thus destabilized"

b.) This Answer on ChemSE which clearly states that its Non-Aromatic in
Nature

c.) Also this NEPTL site which clearly states that:

Cyclopropene is not aromatic because one of its ring atoms is sp3
hybridized so it does not fulfill the criterion for aromaticity. But
the cyclopropenyl cation is aromatic because it has an uninterrupted
ring of p-orbital and (4n+2) π-system. The cyclopropenyl anion is
antiaromatic as it has (4n) π-system.

2.) Arguments for cycloheptatrienyl anion

a.) This Question on ChemSE where the same question have 2 deflecting answer this answer is saying is that the anoin is antiaromatic and this states that the anion is nonaromatic

b.) Also my book (solomons and fryhle organic chemistry adapted for JEE) gives this as Antiaromatic

I don't know which one is correct, please help by providing a comprehensive answer with a reason that can be applied everywhere in such questions.

organic-chemistry aromaticity

share|improve this question

asked 4 hours ago

Advil SellAdvil Sell

14913

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Basically the SE answer you mention should fiv your current Q as well. Given the existance of a species that results in antiaromaticuty, then ist that the species avoid it. The key is that antiaromaticity is forced, it serves to determine if a formally conjugated system does indeed undergo delocalosation, not to establish its existence.
  $endgroup$
  – Alchimista
  1 hour ago
  
  
  

  
  
  
  

add a comment | 

2

$begingroup$

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 Cyclopropenyl Anion

a.) Wikipedia which under the heading of "Effects on reactivity"
clearly states that :

"However, the cyclopropenyl anion has 4 π electrons in a cyclic system
and in fact has a substantially higher pKa than 1-propene because it
is antiaromatic and thus destabilized"

b.) This Answer on ChemSE which clearly states that its Non-Aromatic in
Nature

c.) Also this NEPTL site which clearly states that:

Cyclopropene is not aromatic because one of its ring atoms is sp3
hybridized so it does not fulfill the criterion for aromaticity. But
the cyclopropenyl cation is aromatic because it has an uninterrupted
ring of p-orbital and (4n+2) π-system. The cyclopropenyl anion is
antiaromatic as it has (4n) π-system.

2.) Arguments for cycloheptatrienyl anion

a.) This Question on ChemSE where the same question have 2 deflecting answer this answer is saying is that the anoin is antiaromatic and this states that the anion is nonaromatic

b.) Also my book (solomons and fryhle organic chemistry adapted for JEE) gives this as Antiaromatic

I don't know which one is correct, please help by providing a comprehensive answer with a reason that can be applied everywhere in such questions.

organic-chemistry aromaticity

share|improve this question

asked 4 hours ago

Advil SellAdvil Sell

14913

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Basically the SE answer you mention should fiv your current Q as well. Given the existance of a species that results in antiaromaticuty, then ist that the species avoid it. The key is that antiaromaticity is forced, it serves to determine if a formally conjugated system does indeed undergo delocalosation, not to establish its existence.
  $endgroup$
  – Alchimista
  1 hour ago
  
  
  

  
  
  
  

add a comment | 

$begingroup$

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 Cyclopropenyl Anion

a.) Wikipedia which under the heading of "Effects on reactivity"
clearly states that :

"However, the cyclopropenyl anion has 4 π electrons in a cyclic system
and in fact has a substantially higher pKa than 1-propene because it
is antiaromatic and thus destabilized"

b.) This Answer on ChemSE which clearly states that its Non-Aromatic in
Nature

c.) Also this NEPTL site which clearly states that:

Cyclopropene is not aromatic because one of its ring atoms is sp3
hybridized so it does not fulfill the criterion for aromaticity. But
the cyclopropenyl cation is aromatic because it has an uninterrupted
ring of p-orbital and (4n+2) π-system. The cyclopropenyl anion is
antiaromatic as it has (4n) π-system.

2.) Arguments for cycloheptatrienyl anion

a.) This Question on ChemSE where the same question have 2 deflecting answer this answer is saying is that the anoin is antiaromatic and this states that the anion is nonaromatic

b.) Also my book (solomons and fryhle organic chemistry adapted for JEE) gives this as Antiaromatic

I don't know which one is correct, please help by providing a comprehensive answer with a reason that can be applied everywhere in such questions.

organic-chemistry aromaticity

share|improve this question

asked 4 hours ago

Advil SellAdvil Sell

14913

$endgroup$

share|improve this question

asked 4 hours ago

Advil SellAdvil Sell

14913

share|improve this question

asked 4 hours ago

Advil SellAdvil Sell

14913

asked 4 hours ago

Advil SellAdvil Sell

14913

asked 4 hours ago

Advil SellAdvil Sell

14913

1 Answer
1

active

oldest

votes

2

$begingroup$

Whenever you want a definition of a chemical concept, you should refer to the IUPAC's Gold Book which in this case states that antiaromatic compounds are

compounds that contain 4 n(n ≠ 0) π-electrons in a cyclic planar, or nearly planar, system of alternating single and double bonds, e.g. cyclobuta-1,3-diene.

A corollary to this rule is that all the atoms must have an sp2-hybridization, so the orbitals can overlap. However, the carbon bearing the negative charge has an sp3-hybridization, i.e. they does not count as π-electrons but σ-electrons and that breaks the rule of alternating single and double bonds. So both anions are non-aromatic.

Edited after the OP opened my eyes on a big mistake I had made in answering his question. Sorry about that.

share|improve this answer

edited 1 hour ago

answered 2 hours ago

SteffXSteffX

1,86639

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  as i know that alternating single and double bond means conjugation but as chemistry.stackexchange.com/a/51470/73826 this answer suggest the carbanion moves out of plane and hence can't remain in conjugation ......please clear this in the answer
  $endgroup$
  – Advil Sell
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Oh damn, I am an idiot! I was picturing a cation in my head, with an empty sp2 orbital. You can insult me if you want, I deserve it! I am gonna edit my answer immediately.
  $endgroup$
  – SteffX
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  That is kind of you. I have edited my answer.
  $endgroup$
  – SteffX
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I dont know if I am wrong that some ring with a -ve charge are aromatic in which the electrons are considered as $pi$ electron and thus the congugation is present , can you explain why they aren't considered as $pi$ electrons here ???
  $endgroup$
  – Advil Sell
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Oh right, I get it. You actually wonder why the cyclopentadienyl anion is aromatic, and the anion center is sp2 in that case, whereas it is not in the case with cycloheptadienyl anion. Well hybridization occurs only if it helps getting a lower potential energy or, in other terms, if there is an incentive to do so. There is an incentive to change hybridization to go aromatic, but not to go antiaromatic.
  $endgroup$
  – SteffX
  1 hour ago
  

  
  
  
  

add a comment | 

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2

$begingroup$

Whenever you want a definition of a chemical concept, you should refer to the IUPAC's Gold Book which in this case states that antiaromatic compounds are

compounds that contain 4 n(n ≠ 0) π-electrons in a cyclic planar, or nearly planar, system of alternating single and double bonds, e.g. cyclobuta-1,3-diene.

A corollary to this rule is that all the atoms must have an sp2-hybridization, so the orbitals can overlap. However, the carbon bearing the negative charge has an sp3-hybridization, i.e. they does not count as π-electrons but σ-electrons and that breaks the rule of alternating single and double bonds. So both anions are non-aromatic.

Edited after the OP opened my eyes on a big mistake I had made in answering his question. Sorry about that.

share|improve this answer

edited 1 hour ago

answered 2 hours ago

SteffXSteffX

1,86639

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  as i know that alternating single and double bond means conjugation but as chemistry.stackexchange.com/a/51470/73826 this answer suggest the carbanion moves out of plane and hence can't remain in conjugation ......please clear this in the answer
  $endgroup$
  – Advil Sell
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Oh damn, I am an idiot! I was picturing a cation in my head, with an empty sp2 orbital. You can insult me if you want, I deserve it! I am gonna edit my answer immediately.
  $endgroup$
  – SteffX
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  That is kind of you. I have edited my answer.
  $endgroup$
  – SteffX
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I dont know if I am wrong that some ring with a -ve charge are aromatic in which the electrons are considered as $pi$ electron and thus the congugation is present , can you explain why they aren't considered as $pi$ electrons here ???
  $endgroup$
  – Advil Sell
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Oh right, I get it. You actually wonder why the cyclopentadienyl anion is aromatic, and the anion center is sp2 in that case, whereas it is not in the case with cycloheptadienyl anion. Well hybridization occurs only if it helps getting a lower potential energy or, in other terms, if there is an incentive to do so. There is an incentive to change hybridization to go aromatic, but not to go antiaromatic.
  $endgroup$
  – SteffX
  1 hour ago
  

  
  
  
  

add a comment | 

2

$begingroup$

Whenever you want a definition of a chemical concept, you should refer to the IUPAC's Gold Book which in this case states that antiaromatic compounds are

compounds that contain 4 n(n ≠ 0) π-electrons in a cyclic planar, or nearly planar, system of alternating single and double bonds, e.g. cyclobuta-1,3-diene.

A corollary to this rule is that all the atoms must have an sp2-hybridization, so the orbitals can overlap. However, the carbon bearing the negative charge has an sp3-hybridization, i.e. they does not count as π-electrons but σ-electrons and that breaks the rule of alternating single and double bonds. So both anions are non-aromatic.

Edited after the OP opened my eyes on a big mistake I had made in answering his question. Sorry about that.

share|improve this answer

edited 1 hour ago

answered 2 hours ago

SteffXSteffX

1,86639

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  as i know that alternating single and double bond means conjugation but as chemistry.stackexchange.com/a/51470/73826 this answer suggest the carbanion moves out of plane and hence can't remain in conjugation ......please clear this in the answer
  $endgroup$
  – Advil Sell
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Oh damn, I am an idiot! I was picturing a cation in my head, with an empty sp2 orbital. You can insult me if you want, I deserve it! I am gonna edit my answer immediately.
  $endgroup$
  – SteffX
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  That is kind of you. I have edited my answer.
  $endgroup$
  – SteffX
  1 hour ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I dont know if I am wrong that some ring with a -ve charge are aromatic in which the electrons are considered as $pi$ electron and thus the congugation is present , can you explain why they aren't considered as $pi$ electrons here ???
  $endgroup$
  – Advil Sell
  1 hour ago
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  Oh right, I get it. You actually wonder why the cyclopentadienyl anion is aromatic, and the anion center is sp2 in that case, whereas it is not in the case with cycloheptadienyl anion. Well hybridization occurs only if it helps getting a lower potential energy or, in other terms, if there is an incentive to do so. There is an incentive to change hybridization to go aromatic, but not to go antiaromatic.
  $endgroup$
  – SteffX
  1 hour ago
  

  
  
  
  

add a comment | 

$begingroup$

Whenever you want a definition of a chemical concept, you should refer to the IUPAC's Gold Book which in this case states that antiaromatic compounds are

compounds that contain 4 n(n ≠ 0) π-electrons in a cyclic planar, or nearly planar, system of alternating single and double bonds, e.g. cyclobuta-1,3-diene.

A corollary to this rule is that all the atoms must have an sp2-hybridization, so the orbitals can overlap. However, the carbon bearing the negative charge has an sp3-hybridization, i.e. they does not count as π-electrons but σ-electrons and that breaks the rule of alternating single and double bonds. So both anions are non-aromatic.

Edited after the OP opened my eyes on a big mistake I had made in answering his question. Sorry about that.

share|improve this answer

edited 1 hour ago

answered 2 hours ago

SteffXSteffX

1,86639

$endgroup$

share|improve this answer

edited 1 hour ago

answered 2 hours ago

SteffXSteffX

1,86639

answered 2 hours ago

SteffXSteffX

1,86639

answered 2 hours ago

SteffXSteffX

1,86639