Engineering Chemistry MCQ (Conformations)

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Engineering Chemistry MCQ (Conformations)

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1. Conformations are different arrangements of atoms that can be converted into one another by rotation about ___________
a) Covalent bond
b) Double bond
c) Single bond
d) Triple bond
Answer: c
Explanation: Conformational isomerism is a form of stereoisomerism in which the
isomers can be interconverted exclusively by rotations about formally single bonds.
Such isomers are generally referred to as conformational isomers or conformers
and, specifically, as rotamers.

2. The energy required to rotate n-butane molecule about the carbon-carbon bond is called ___________
a) Rotational energy
b) Torsional energy
c) Enantiomeric energy
d) Potential energy
Answer: b
Explanation: The energy required to rotate n-butane molecule about the carboncarbon bond is called torsional energy. Torsion energy can be used to solve
problems of general relativity especially the singularity problem.

3. The rotation about the (C2 – C3) carbon-carbon bond of n-butane requires the energy of about ___________
a) 100 kJ/mol
b) 50 kJ/mol
c) 10 kJ/mol
d) 3 kJ/mol
Answer: d
Explanation: The rotation about the (C2 – C3) carbon-carbon bond of n-butane
requires the very less energy of about 3kJ/mol. It requires very less amount of
energy.

4. The infinity of intermediate conformations are called ___________
a) Skew conformations
b) Staggered conformations
c) Eclipsed conformations
d) Gauche

5. The potential energy of n-butane is minimum for ___________
a) Skew conformations
b) Staggered conformations
c) Eclipsed conformations
d) Gauche
Answer: b
Explanation: The potential energy of n-butane is minimum for staggered
conformations. It is because of no steric hindrance.

6. The relative instability of any of the intermediate skew conformations is due to ___________
a) Lateral strain
b) Shear strain
c) Longitudinal strain
d) Torsional strain
Answer: c
Explanation: The potential energy of n-butane is maximum for eclipsed
conformations. It is because of overlapping of functional groups.

7. In gauche conformations, the methyl groups are ___________
a) 600 apart
b) 900 apart
c) 1800 apart
d) 3600 apart
Answer: a
Explanation: In gauche conformations, the methyl groups are 600 apart. In general a gauche rotamer is less stable than an anti-rotamer.

8. Both anti and gauche conformations are free of torsional strain.
a) True
b) False
Answer: a
Explanation: Both anti and gauche conformations are free of torsional strain. In
general, a gauche rotamer is less stable than an anti-rotamer.

9. Gauche conformation is less stable due to _______________
a) Hydrogen bonding
b) Covalent bonding
c) Vander Waal’s repulsion
d) Torsional strain
Answer: c
Explanation: Gauche conformation is less stable due to Vander Waal’s repulsion.
Vander Waal’s are weak forces of attraction which results in lesser stability of
gauche conformer.

11. Which of the following is least stable?
a) Anti conformation
b) Gauche conformation
c) Staggered conformation
d) Eclipsed conformation
Answer: d
Explanation: Eclipsed conformation is the least stable due to its high torsional
energy. The potential energy of n-butane is maximum for eclipsed conformations.

12. Potential energy remains same during the rotation about the carbon-carbon of
n-butane.
a) True
b) False
Answer: b
Explanation: Potential energy changes during the rotation about the carbon-carbon
of n-butane. The potential energy of n-butane is maximum for eclipsed
conformations and minimum for staggered conformations