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Monday, June 13, 2022

Is Cyclocta-1,3,5,7-tetraene (COT) is aromatic, anti-aromatic OR non- aromatic?

Cyclocta-1,3,5,7-tetraene (COT) have four double bonds  and four single bond alternatively hence their is lack of  resonance. The reason behind this is bigger size of ring and finally  cyclocta-1,3,5'7-tetraene is to be non-planar.
The structure is:


However, the compound have four  double bonds  means eight (8) π electrons.

It may be aromatic, it has to have 4n+2 electrons (2, 6, 10, etc.).

Anti-aromatic systems have 4n electrons (4, 8, 12, etc.).

It may be expected that the molecule was planar and anti-aromatic.

However, actually the molecule takes a tub-shaped (non planer ) conformation in its native state. Since, it is not a planar molecule, it becomes non-aromatic instead of anti-aromatic.

Related Questions:

  1. How is base strength related to the availabihty of the electron-pair?
  2. Amines are more basic than ammonia why?
  3. What is relative basic strength order 1° amines , 2°amines and 3° amines ? Explain:
  4. Give an explanation for the fact that Guanidine NH=C(CH3)2 is a stronger base than most of amines?
  5. Arrange in correct order of basic Character of aniline, pyrrol, pyridine and piperidine?
  6. What is correct basicity order of pyridine, pyridazine, pyrimidine and pyrazine ?
  7. Give an explanation for the fact that Guanidine NH=C(CH3)2 is a stronger base than most of amines?
  8. Arrange in correct order of basic Character of aniline, pyrrol, pyridine and piperidine?
  9. What is correct basicity order of pyridine, pyridazine, pyrimidine and pyrazine ?
  10. Why pyridine is more basic than Pyrrole?
  11. Why pyrimidine is less basic than pyridine?
  12. Imidazole is more basic than pyridine? Why?
  13. Biological Important of Imidazole and structure:
  14. Pyridine is almost 1 million times less basic than piperidine? Why?
  15. Cyclohexylamine amine is the stronger base than Aniline? Why?
  16. Tetrahydroquinoline amine is the stronger base than Tetrahydroisoquinoline? Why?
  17. Arrange the following in the order of increasing basicity : p-Toluidine, N, N-Dimethyl-p-toluidine, p-Nitroaniline, Aniline. (I.I.T.1986)
  18. Arrange the following in the increasing order of their acid strength : Methyl amine, Dimethyl amine, Aniline, N-methyl aniline (I.I.T, 1988).


Thursday, June 9, 2022

Resonance energy:

The energy differecnce between most stable resonating structure and resonance hybrid is known as
resonance energy.
 (1) It ís the experimental value which is calculated by heat of hydrogenation (HOH).
(2) Higher the value of resonance energy, greater is the resonance stabilization.

Resonance Energy of Benzene :
The experimental value heat of hydrogenation for benzene is 51 Kcal.
The resonance energy of benzene is calculated fromthe heat of hydrogenation as given below :
Resonance energy comparison:

(1) Consider better resonance or equivalent resonating structures,molecules having equivalent resonating
structures must have more resonance energy, than non-equivalent resonating structures.
(2) Aromatic compound have more resonance energythan non-aromatic compound. 
(3) In case of larger conjugation, more will be the Resonance energy.
(4) Resonance energy will be more, when π-bond, lone pair conjugation is present than π, π-conjugation

Related questions;

(1) What is Steric Inhibition in Resonance of SIR effect ?

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