Heterocyclic Compounds Unit III

In pyrrole and pyridine the number of electrons that the N atom contributes to n-system is

• Pyrrole 2, pyridine 1

• Pyrrole 1, pyridine 1

• Pyrrole 2, pyridine 2

• Pyrrole 1, pyridine 2

What is the correct order of reactivity most reactive first of pyrrole, furan and thiophene towards electrophiles

• furan>thiophene>pyrrole

• pyrrole>furan>thiophene

• furan>pyrrole> Thiophene

• None of above

Electrophilic substitution on furan usually occurs at:

• C1

• C2

• C1 & C2

• None of above

Nitration of pyrrole is best carried out using

• Concentrated nitric acid and sulfuric acid

• Acetyl nitrite

• Ammonium nitrate

• All of above

If you wanted to form 2,3,4,5-tetrabromopyrrole from pyrrole, which of the following conditions would be the best choice

• HBr₂ at 298K

• Br₂ with AlBr₃ as a Lewis catalyst

• Br₂ at 273K

• Br₂ in presence of radical initiation

Which statement below is correct...

• Pyrrole is stronger base than triethylamine

• Pyrrole readily protonated on the N atom

• Pyrrole is a very weak base

• None of above

Which statement about thiophene is incorrect

• Thiophene is polar

• The S atom contributes two electrons to the n-system

• Thiophene is less reactive than pyrrole

• Thiophene is more reactive than pyrrole

Pyrrole undergoes sulfonation in presence of…..................to produce pyrrole-2-sulfonic acid

• Conc H₂SO₄ + HNO₃

• Conc H₂SO₄

• Dilute sulphuric acid pyridine

• SO₃ and ethanol

Pyrrole undergoes iodination in presence of iodine and potassium iodine to produce…

• 2-iodo pyrrole

• 3-iodo pyrrole

• tetra iodo pyrrole

• tri iodo pyrrole

Oxidation of pyrrole in presents of chromium oxide (Cr₂O₃) and acetic acid produce

• Malic acid

• Pyrrole-N-oxide

• None of above