250+ TOP MCQs on Organic Chemistry – Isomerism and Answers

Chemistry Multiple Choice Questions on “Organic Chemistry – Isomerism”.

1. 2-chloropropane and 1-chloropropane exhibit ____________ isomerism.
a) chain
b) position
c) functional
d) metamerism
Answer: b
Clarification: When two or more compounds have the same molecular formula but the different position of functional groups are substituents, they are called positional isomers and the phenomenon is called position isomerism. Here 2-chloropropane and 1-chloropropane differ in position so they exhibit position isomerism.

2. Which of the following is not a type of structural isomerism?
a) geometric isomerism
b) chain isomerism
c) metamerism
d) tautomerism
Answer: a
Clarification: Structural isomerism is a type of isomerism, compounds have the same molecular formula but different structures there can be further divided into types: chain isomerism, position isomerism, functional isomerism, metamerism, and tautomerism. Therefore geometric isomerism is not a type of structural isomerism.

3. Optical isomerism is a type of ____________
a) metamerism
b) stereoisomerism
c) geometrical isomerism
d) tautomerism
Answer: b
Clarification: The compounds having the same molecular formula but the different spatial arrangement of atoms or groups are stereoisomers and the phenomenon is called stereoisomerism. it is of three types namely optical isomerism, geometrical isomerism, and conformations.

4. The d-form is also known as ____________
a) rotatory
b) laevorotatory
c) dextrorotatory
d) l-form
Answer: c
Clarification: The isomer which rotates the plane of polarized light towards the right that is clockwise, is known as a dextrorotatory or d form while that which rotates towards the left that is anti-clockwise, is known as laevorotatory or l-form.

5. Enantiomers are same as diastereomers.
a) true
b) false
Answer: b
Clarification: In optical isomerism, enantiomers are nonsuperimposable mirror images while diastereomers are the isomers which are nonsuperimposable and not related to each other as mirror images, they also have different physical and chemical properties.

6. How many planes of symmetry does a meso compound have?
a) 2
b) 1
c) 3
d) 4
Answer: b
Clarification: The compound whose half part of a molecule is a mirror image of the other half, is called meso form. Generally, a meso compound has two or more chiral centers and one plane of symmetry. the compound in meso form is optically inactive due to internal compensation.

7. If a compound has 3 chiral carbons What is the number of optically active isomers?
a) 9
b) 3
c) 4
d) 8
Answer: d
Clarification: The number of optically active isomers for a compound is given as 2ⁿ where, n represents the number of chiral carbons in that particular carbon, here as the compound has 3 chiral carbons n = 3, so the number of optically active isomers equals 2³ = 8.

8. Acetaldehyde and ethenol show ____________
a) stereoisomerism
b) metamerism
c) positional isomerism
d) tautomerism
Answer: d
Clarification: The compounds acetaldehyde and ethenol exhibit tautomerism. Tautomerism is a special type of functional isomerism which arises in carbonyl compounds containing α-hydrogen atom, it is a change of keto form to enol form.

9. A compound with the same molecular formula exists in two forms one is alcohol and the other is Ether, what type of isomerism does it show?
a) metamerism
b) positional isomerism
c) functional isomerism
d) chain isomerism
Answer: c
Clarification: Functional isomerism arises when two or more compounds having the same molecular formula but the different functional group. An example is that C₃H₆O represents an aldehyde as well as a Ketone, therefore we can say that the above compound which is alcohol, as well as Ether, shows functional isomerism.

10. What is the specific rotation if its observed rotation is given as 3x, its length is given as x and density is given as 3/y?
a) 2y
b) 3y
c) y
d) 4y
Answer: c
Clarification: The specific rotation is given by the expression observed rotation/length X density, here as observed rotation is given as 3x and its length is given as x, while the density is 3/y, the specific rotation equals 3x/x(y/3) = y.