This set of Engineering Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Optical Isomerism”.
1. Optical activity is the property in which a substance is unable to rotate the plane of polarisation.
a) True
b) False
View Answer
Explanation: Optical activity is the property in which a substance is able to rotate the plane of polarisation of plane polarised light.
2. Select the incorrect statement from the following option.
a) Racemic modification is an equimolar mixture of dextrorotatory and levorotatory isomers
b) Meso compounds contain more than one chiral carbon centre
c) Meso compounds are externally compensated
d) Racemic mixture is designated as dl-pair
View Answer
Explanation: Meso compounds are internally compensated form whereas racemic mixtures are externally compensated modification. All the other options are correct.
3. Select the correct statement from the following option.
a) Meso compound possess both plane of symmetry and centre of symmetry
b) Meso compound possess either plane or centre of symmetry
c) Meso compound does not possess either plane or centre of symmetry
d) Meso compounds are externally compensated form
View Answer
Explanation: Meso compound possess either plane or centre of symmetry. They do not possess both plane of symmetry and centre of symmetry and also they are internally compensated form.
4. How many optical isomers are possible in a compound with one chiral carbon?
a) 5
b) 4
c) 2
d) 3
View Answer
Explanation: A compound with one chiral carbon has three optical isomers (+), (-) and (±).
5. Which of the following compound would show optical isomerism?
a) CH3 – CH(OH) COOH
b) H2N CH(CH3)2
c) (CH3)2 CHCHO
d) H2N CH2 COOH
View Answer
Explanation: CH3 – CH(OH) COOH will show optical isomerism as it possess chiral carbon.
6. The number of configurational isomers of molecules having (n) different chiral carbons is ____________
a) 2n
b) 2n
c) 2n-1
d) 2n+1
View Answer
Explanation: The number of configurational isomers of molecules having (n) different chiral carbons is 2n. It is calculated mathematically.
7. The number of racemic forms of molecules having (n) different chiral carbons is ____________
a) 2n
b) 2n
c) 2n-1
d) 2n+1
View Answer
Explanation: The number of racemic forms of molecules having (n) different chiral carbons is 2n-1 whereas the number of configurational isomers of molecules having (n) different chiral carbons is 2n.
8. For a molecule with two like chiral carbon atoms, the number of optically inactive form is?
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: For a molecule with two like chiral carbon atoms, the number of optically inactive form is one. This is always used for the calculation of optically inactive forms.
9. For a molecule with two like chiral carbon atoms, the number of optically active form is?
a) 4
b) 3
c) 1
d) 2
View Answer
Explanation: For a molecule with two like chiral carbon atoms, the number of optically active form is two. This is always used for the calculation of optically active forms.
10. Find the number of stereoisomers for CH3 – CHOH – CH = CH – CH3.
a) 1
b) 2
c) 3
d) 4
View Answer
Explanation: The number of stereoisomers for CH3 – CHOH – CH = CH – CH3 is four. This is calculated by the formula 2n+1.
11. The necessary condition for showing optical activity is the chirality of a molecule as a whole.
a) True
b) False
View Answer
Explanation: The necessary condition for showing optical activity is the chirality of a molecule as a whole. It is the most important condition for showing optical activity.
12. The sufficient condition for showing optical activity is _______________
a) Molecule should have measurable amount of optical activity only
b) Polarimeter should have capacity of recording low-degree optical activity only
c) Chirality of molecule as a whole only
d) Both, the molecule should have measurable amount of optical activity and polarimeter should have capacity of recording low-degree optical activity
View Answer
Explanation: The molecule should have measurable amount of optical activity and polarimeter should have capacity of recording low-degree optical activity.
13. Which of the following is an example of optically active compounds without chirality?
a) Tartaric acid
b) Sulfhonium salt
c) Diphenic acid
d) Glyceraldehyde
View Answer
Explanation: Sulphhonium salt is an example of optically active compounds without chirality. It is a special case. There are various such molecules which are optically active compounds without chirality.
14. Spiranes exhibit optical isomerism because of restricted rotation.
a) True
b) False
View Answer
Explanation: Spiranes exhibit optical isomerism because of restricted rotation. They cannot rotate about any axis.
15. Which of the following is not optically active compound?
a) 1,7- Dicarboxylic spirocycloheptane
b) 1,3- Diphenyl propadiene
c) Meso-tartaric acid
d) Glyceraldehyde
View Answer
Explanation: Meso-tartaric acid is an optically inactive molecule with a chiral carbon atom. It is a special case of optical activity.
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