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Showing posts with label GENERAL ORGANIC CHEMISTRY. Show all posts
Showing posts with label GENERAL ORGANIC CHEMISTRY. Show all posts

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 ?

Tuesday, January 5, 2021

Phenyl group is known to extract negative inductive effect, but each phenyl ring in biphenyl is more reactive than benzene towards Electrophilic substation. Why?

It is because, in biphenyl, one of the phenyl groups acts as donor and the other as electron acceptor. This increases electron density on benzene ring and facilitates Electrophilic attack at ortho and para position.

Related questions;

Thursday, December 17, 2020

Why Guanadine is a strongest base among neutral compounds?

Basicity of Guanidine:
Guanidine is the strongest base among neutral compounds:


The remarkable basicity of guanidine is attributed to the fact that the positive charge on
the guanidinium ion is delocalized equally over the three nitrogen atoms, as shown by
these three equivalent resonating  structures:

Basicity of nitrogen can be increased by attachment to pi-donors (NH2) group. These two pi-donating NH2 groups donate electron density to the (pi-accepting) C=NH. Hence, the guanidinium ion is a highly stable cation. 

Related questions;

What is Steric Inhibition in Resonance of SIR effect ?

Saturday, December 5, 2020

What is the nucleophilicity of halides?

Nucleophilicity of nucleophile is inversely proportional to hydration energy or solvation energy. Fluorine is smallest among hence it highly solvate and more hydration energy ,and hence less nucleophilicity than other halides.

The correct nucleophilicity order is as:
                I- > Br- > Cl- > F-

Thursday, November 19, 2020

Why does aniline not undergo friedel crafts reaction?

 Aniline is basic due to the presence of lone pair of electron on the nitrogen atom of amine group. Where as AlCl3 is a Lewis acid which is used as catalyst in friedel craft reaction. 

Al has a empty orbital  so it accept lone pair electron from amine group hence nitrogen atom of amine acquired positive charge and ring become deactivating. Due to this reason aniline does not undergoes friedel craft reaction.

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).


Saturday, September 12, 2020

Though enol form is less stable than keto form, phenol exists in enol form, why?

Enol form is much more stable than keto form because of great stability associated with aromatic ring which is absent in keto form.



What are the difference between Tautomerism & Resonance ?

(1) In tautomerism, an atom changes place but resonance involves a change of position of pi-electrons or unshared electrons.

(2) Tautomers are different compounds and they can be separated by suitable methods but resonating structures cannot be separated as they are imaginary structures of the same compound.

(3) Two tautomers have different functional groups but there is same functional group in all canonical structures of a resonance hybrid.

(4) Two tautomers are in dynamic equilibrium but in resonance only one compound exists.

(5) Resonance in a molecule lowers the energy and thus stabilises a compound and decreases its reactivity. But no such effects occur in tautomerism.

(6) In resonance, bond length of single bond decreases and that of double bond increases e.g. all six C—C bonds in benzene are equal and length is in between the length of a single and a double bond.

(7) Resonance occurs in planar molecule but atoms of tautomers may remain in different planes as well.

(8) Tautomers are indicated by double arrow in between the two isomers but double headed single arrow is put between the canonical (resonating) structures of a resonating molecule.

Related Questions:

(2) How is base strength related to the availability of the electron-pair

(3) Amines are more basic than ammonia why?

(4) What is relative basic strength order 1° amines , 2°amines and 3° amines ? Explain:

(5) Give an explanation for the fact that Guanidine NH=C(CH3)2 is a stronger base than most of amines?

(6) Arrange in correct order of basic Character of aniline, pyrrol, pyridine and piperidine?

(7) What is correct basicity order of pyridine, pyridazine, pyrimidine and pyrazine ?

(8) Give an explanation for the fact that Guanidine NH=C(CH3)2 is a stronger base than most of amines?

(9) Arrange in correct order of basic Character of aniline, pyrrol, pyridine and piperidine?

(10 What is correct basicity order of pyridine, pyridazine, pyrimidine and pyrazine ?

(11) Why pyridine is more basic than Pyrrole?

(12) Why pyrimidine is less basic than pyridine?

(13) Imidazole is more basic than pyridine? Why?

(14) Biological Important of Imidazole and structure:

(15) 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).


4- nitrophenol is more acidic than 3,5 - dimethyl –4-nitro-phenol. Explain.

It is explained in terms of inductive effect and hyperconjugation.

Explain why aniline is less basic than ammonia?

The lone pair present at the nitrogen in aniline is delocalized in the ring (by 
resonance) and hence, it is not free for protonation, while in ammonia. It is 
present at nitrogen all the time, hence it is readily available for ptrotonation.

Why benzyl carbonium ion is more stable than ethyl carbonium ion?

Due to resonance benzyl carbonation is more stable than ethyl carbonation.

Among orthochlorophenol and orthofluorophenol, which will be a stronger acid and why?


The one having a weaker conjugate base will be a stronger acid. If the conjugate 
base has to be weak, the negative charge has to be delocalised to a larger 
extent.
In o-chlorophenol
Due to the availability of vacant orbitals in chlorine, the negative charge is delocalised to a larger extent. The same cannot take place in case of F as F does not have vacant orbitals. So, o-chlorophenol, having a weaker conjugate base, becomes a stronger acid.

Related Questions
(1)Benzylamine is a stronger base than aniline. Explain.
(2) Why is always the resonance effect dominating over the inductive effect?
(3) Why benzyl carbonium ion is more stable than ethyl carbonium ion.?

Monday, July 20, 2020

What happens if two deactivating and one activating group is present on a benzene ring?

We know that reactivity of benzene ring towards electrophilic reaction depends upon presence of group on benzene ring. Benzene gives electrophilic substitution reaction due to negative pi cloud formation , if there is EWG (electron withdrawing) group on benzene ring it's negativeness decreases and reactivity also decreases and due to resonance upcoming group goes at meta position only while in the presence of ERG (electron releasing groups) it's negative ness increases and reactivity increase and due to resonance upcoming group goes at ortho and para position .
If both EWG and ERG present on benzene ring then upcoming electrophile goes to ortho and para position  according to ERG group .

Sunday, May 31, 2020

Why The phenoxide ion is more stable than phenol ?

The phenoxide ion is more stable than phenol, due to greater dispersal of negative charge, therefore. Equilibrium get shifted to forward direction. whereas alkoxide ion is less stable than alcohols due to intensification of negative charge, so equilibrium get shifted towards backward direction. Hence phenols are more acidic than alcohols. 

Related Questions:

Phenoxide ion is more stable than an alkaoxide. why?

Which is more stable? CH3-CH2+ (Ethyl carbocation) or CH2=CH+ (Vinyl carbocation)? And why?

No Doubt, Ethyl carbocation (CH3-CH2+) is more stable than vinyl carbocation (CH2=CH+). The greater stability of CH3-CH2+ carbocation over vinyl carbocation because the positive charge on the CH2 is stabilised by the inductive effect as well as hyperconjugation  from the neighbouring carbon atom.
But in case of CH2=CH+. The two carbon atoms involved are sp2 hybridised. An sp2 hybridised carbon atom is more electronegative which increases positive charge and increases as the s-character of a hybridised carbon atom increases. As the the result inductive effect decreases by the neighbouring carbon atom. 

Why Guanidine behave as the strongest base among neutral compounds?. explaine the remarkable basicity of guanidine.

Basicity of Guanidine:
Guanidine is the strongest base among neutral compounds:


The remarkable basicity of guanidine is attributed to the fact that the positive charge on the guanidinium ion is delocalized equally over the three nitrogen atoms, as shown by
these three equivalent resonating  structures:

Basicity of nitrogen can be increased by attachment topi-donors (NH2) group. These two pi-donating NH2groups donate electron density to the (pi-accepting) C=NH. Hence, the guanidinium ion is a highly stable cation.

What is Guanidine and its structure , name amino acid which contains guanidine group ?

Guanidine is strongest organic nitrogenous compound with the formula HNC(NH2)2. Guanidine is analogue of carbonic acid. That is, the C=O group in carbonic acid is replaced by a C=NH group, and each OH is replaced by a NH2 group.

A guanidine group also appears in larger organic molecules, including on the side chain of arginine (a basic amino acid).


It is a colourless solid that dissolves in polar solvents. It is a strong base that is used in the production of plastics and explosives. It is found in urine as a normal product of protein metabolism.

What is correct acidic strengths order of the haloforms acids ? Give correct explanation.

We know that acidic strength of the acid also depends upon stability of conjugate bases, so for relative strength of acid, we need to check the relative stabilities of their conjugate bases.

                                                     CF3-, CCl3-, CBr3- CI3-

We are expecting the acidic strength haloform acids asCHF3, CHCl3, CHBr3, CHI3 in decreasing order. Because Fluorine is most electronegative atom so it would be stabilize CF3- more, as electronegativity decreases from F to I the stability of conjugate -ve ion would be but that is not correct the actual order isCHCl3 > CHF3 > CHBr3 > CHI3.

This is because there is effective back bonding in CCl3-and hence the negative charge partially gets stabilised by back donation to the vacant 3d orbitals of Cl. Thus, CHCl3 is a stronger acid than CHF3 and also among them due to 2pπ-3dπ back bonding.


The acidic strengths of the other three haloforms can be compared the inductive effects of their anions. F is very electronegative and hence stabilises the negative charge on the C atom. So, CHF3 is a better acid than CHBr3, and the least acidic is CHI3.

 The overall acidic strength order is:
     CHCl3 > CHF3 > CHBr3 > CHI3.