This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Structure of Pyridine”.
1. Pyridine is a which type of heterocyclic compound from the following options?
a) Six membered heterocyclic compound
b) Seven membered heterocyclic compound
c) Four membered heterocyclic compound
d) Five membered heterocyclic compound
Explanation: Pyridine is a five membered heterocyclic compound. The chemical formula for pyridine is: C5H5N. The only way we can have five carbons, a nitrogen, and only five hydrogens is if the carbons and nitrogen form a ring with alternating double bonds.
2. Which element is present as hetero atom in pyridine?
d) Sulphur and nitrogen
Explanation: Pyridine is an analogue of benzene in which one -CH unit is replaced by N. The chemical formula for pyridine is: C5H5N.
3. The electron of Nitrogen participating in the resonance in pyridine is present in which orbital?
d) sp -orbital
Explanation: In pyridine, from three sp2 orbital, one hybrid orbital is used for one electron which is utilized in the π-cloud.
4. Pyridine is a not a planner compound?
Explanation: Pyridine is planner monocyclic compound and contains 6 πe- the aromatic sextet. It fulfils the criteria for the Huckel’s rule.
5. How many number of resonating structure stabilises a pyridine molecule?
Explanation: Like benzene, pyridine also has 2 kekule structure (a and b) along with 3 more resonating structure (c, d and e) which contributes to a lesser extent to the stability of molecule.
6. Pyridine come under which category of heterocycle classification on the basis of chemical behavior?
a) -excessive heterocycle
b) -deficient heterocycle
c) -equivalent heterocycle
d) can’t say about the five membered rings
Explanation: Nitrogen is more electronegative than other carbon atom in pyridine, so distribution of 6 e– is unequal (more electron on N).
7. What is the smallest angle in pyridine ring?
Explanation: As shown in below diagram, the angle between C-N-C is the smallest angle which is 116.7°.
8. What is the dipole moment of the pyridine?
b) 2.2 D
c) 1.17 D
d) 4.3 D
9. Which of the following is the correct range for the bond length in the pyridine molecule?
a) 1.34 – 1.40 A°
b) 1.24 – 1.32 A°
c) 2.4 – 2.49 A°
d) 1.02 – 1.17 A°
Explanation: As shown in below diagram, 1.34 – 1.40 A° is the correct range for the bond length in the pyridine molecule.
10. What is the greatest angle in pyridine ring?
Explanation: As shown in below diagram, the angle between C-C-N is the greatest angle which is 124°.
Sanfoundry Global Education & Learning Series – Organic Chemistry.
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