The order of reactivity in five-membered heterocycles is : pyrrole > furan > thiophene > benzene (for comparison). reason is the same as for pyrrole. … The transition state with oxygen atom positively charged resulting from the electrophilic attack on furan is, therefore, less stable than that of pyrrole.
Is pyrrole most stable?
Pyrrole is weakly basic, with a conjugate acid pKa of −3.8. The most thermodynamically stable pyrrolium cation (C4H6N+) is formed by protonation at the 2 position. Substitution of pyrrole with alkyl substituents provides a more basic molecule—for example, tetramethylpyrrole has a conjugate acid pKa of +3.7.
Why is furan more basic than pyrrole?
No, furan should be more basic than pyrrole. This is because nitrogen(in pyrrole) has only one lone pair which is delocalised. However, oxygen in furan has two one pairs. One of these lone pairs is delocalised while the other is localised in an sp2 hybrid orbital.
Why is thiophene least basic?
Pyrrol, furan or thiophene don’t have any bond pair electrons free to release which is why they shouldn’t be basic, but the lecturer of organic chemistry is saying that they are basic as they react with hydrochloric acid to form salts.
Why pyrrole is a weak base?
Pyrrole is an exceedingly weak base. The pair of electrons of the nitrogen atom interacts with the four electrons of the two carbon-carbon double bonds to give an aromatic six-π-electron system similar to that of benzene. … One of its nitrogen atoms resembles that of pyrrole, and is not basic.
Why is pyrrole electrophilic substitution?
Aromatic compounds such as pyridine and pyrrole can also undergo electrophilic substitution reactions with electrophiles. … For pyrrole, electrophilic substitution will occur on the second carbon because it will create three resonance-stabilized forms.
Why is pyrrole more reactive?
And pyrrole, furan, and thiophene are all more reactive than benzene with EAS because the lone pair on the heteroatom can donate electron density into the ring by resonance, thus stabilizing the carbocation intermediate more effectively.
Is pyrrole more basic than aniline?
On other hands, aniline is also aromatic but the lone pair of electrons of NH2 group in aniline is delocalized over the benzene ring, it is not involved in aromatization. This lone pair is still available for proton, hence Aniline is the stronger base than Pyrrole.
What happens when thiophene undergoes Sulphonation?
Thiophenes undergo hydrogenolysis to form hydrocarbons and hydrogen sulfide. Thus, thiophene itself is converted to butane and H2S.
Why thiophene is called super aromatic?
Thiophene is aromatic because it has six π electrons in a planar, cyclic, conjugated system.
What is common between furan pyrrole and thiophene?
The key difference between pyrrole furan and thiophene is that pyrrole contains a –NH group in a five-membered carbon ring and furan contains an oxygen atom in a five-membered carbon ring whereas thiophene contains a sulfur atom in a five-membered carbon ring. Pyrrole furan and thiophene are organic compounds.
Which is more stable pyrrole or pyridine?
The greater stability of the pyrrole is due to its ability to form a conjugated system of pi electrons. … Hence, the lone pair of electrons present on the nitrogen atom in pyridine has the ability to donate a hydrogen ion easily or a Lewis acid. Thus, pyridine is a stronger base than pyrrole.
Is pyridine more aromatic than thiophene?
Therefore, according to me, the aromaticity order should be: benzene > pyridine > pyrrole > furan > thiophene.
Is pyrrole more aromatic than pyridine?
Pyrrole is a much weaker base than pyridine (see above). This is because the lone pair on the N atom is already involved in the aromatic array of p electrons. Protonation results in loss of aromaticity and is therefore unfavourable.
Why is pyrrole more reactive to electrophilic substitution than pyridine?
Pyrrole is more reactive than pyridine for electrophilic substitution reactions because of the stability of the protonated pyrrole intermediate. Pyridine is more stable in its unreacted state compare to pyrrole due to its aromatic nature.
Which position of pyrrole is more reactive towards Electrophile and why?
Pyrrole, thiophene, and furan gives electrophilic aromatic substitution reaction. These compounds are more reactive compared to benzene. Electrophiles majorly attack on 2nd position rather than 3rd position in these heterocyclic compounds.
Why is thiophene more reactive than benzene?
The resonance stabilization energy of benzene is greater than that of these heteroaromatic compounds. The order of aromaticity is benzene > thiophene > pyrrole > furan. All three of these ring systems undergo electrophilic aromatic substitution and are much more reactive than benzene.
What is the reason behind the stability of pyrrole chemical?
Because the nitrogen lone pair is part of the aromatic sextet the electrons are very stable and are much less available for bonding to a proton (and if they do pick up a proton, the molecule loses aromaticity). Pyrrole is a very weak base: the conjugate acid, the pyrrolium ion, is a strong acid with a pKa of 0.4.
What position does pyrrole undergoes electrophilic substitution?
More is the resonating structures; more will be the stable compound. Thus, when a pyrrole undergoes electrophilic aromatic substitution, substitution occurs at the 2nd position of the pyrrole.
Which position of pyrrole is more reactive towards electrophiles?
2-position of pyrrole is more reactive towards electrophilic substitution than 3-position.
Why is pyrrole unstable in strongly acidic solution?
The resonance hybrid of pyrrole indicates that there is a partial positive charge on the nitrogen. Pyrrole is unstable in strongly acid solution because the protonated pyrrole polymerizes. Pyrrole’s acidity is increased due to its conjugated base being stabilized by resonance.
Why is pyrrole amphoteric?
The heteroatom is nitrogen and is responsible for the basicity of many compounds. Nitrogen free electrons are involved in the electron cloud of the ring. … Pyrrole is therefore an amphoteric compound, ie, can behave as an acid and a base.
Which is more basic pyrrole or indole?
Basicity. Unlike most amines, indole is not basic: just like pyrrole, the aromatic character of the ring means that the lone pair of electrons on the nitrogen atom is not available for protonation. Strong acids such as hydrochloric acid can, however, protonate indole.