Important Questions for CSIR NET Chemical Science - Heterocyclic Chemistry

By Astha Singh|Updated : March 31st, 2022

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Most Important Questions Heterocyclic Chemistry

4. Pyridine is considered to be less basic than aliphatic amine because the lone pair of electrons on the N-atom in pyridine resides in:

A. sp hybrid orbital
B. sp3hybrid orbital
C. sp2hybrid orbital
D. sp3d hybrid orbital

5. Predict the product which will be formed on passing a mixture of furan, ammonia, and steam overheated alumina.

a<b<c<d
B. d<b<a<c
C. c<b<a<d
D. b<d<c<a

7. Determine the major products X and Y formed in the reaction given below.

During the nitration of Pyridine which of the following is the major product?

A. nitropyridine
B. 2,3-dihydropyridine
C. 4-nitropyridine
D. 3-nitropyridine

10. Acridine on Bromination gives:

Answers

Solutions

Solution 06:

Compound (b) – pyrrole: Lone pair of electrons on nitrogen is involved in delocalization and protonation will make it anti-aromatic. Hence, it is the least basic of the four compounds.

Compound (d) is aniline: The lone pair on the nitrogen atom is used in the delocalization of pi electrons of the ring. It doesn’t lose its aromatic character on protonation. That’s why it's more basic than pyrrole.

The lone pair of electrons on nitrogen in Compound (c)-pyridine, is present in the sp2 orbital and in compound (a) is piperidine where electrons are present in the sp3 orbitals do not participate in delocalization of the ring pi- electrons and are available for protonation.

Aromatic compounds are less basic than antiaromatic compounds, that’s why pyridine is less basic than piperidine.

Solution 07:

As lone pairs of nitrogen can be delocalized. So, it will be basic in nature and behave as a good nucleophile. In the second reaction, NaH (base) abstracts an acidic proton in order to form Na-Salt of Indole followed by Nucleophilic substitution reactions on indole nitrogen.