Isomerism Test

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Isomerism Test - 6

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Question 1
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Direction (Q. Nos. 1-13) This section contains 13 multiple choice questions. Each question has four
choices (a), (b), (c) and (d), out of which ONLY ONE option is correct.
Q.
Which among the following defines Meso forms of isomers

A
Meso form is optically inactive due to external compensation

B
The molecules of the meso isomers are chiral

C
It can be separated into optically active enantiometric pairs

D
It is a single compound

Solution

a) False, meso form is optically inactive due to presence of Plane of symmetry, centre of symmetry or axis of symmetry and not due to external compensations.
b) False, since meso is optically inactive, so they are achiral
c) False, they can’t be separated into optically active enantiomeric pairs
d) True, it is a single compound.
Question 2
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The molecular formula C₅H₁₂ contains how many isomeric alkanes?

A
1

B
2

C
3

D
4

Solution

To have three isomeric monochlorides, the isomer of the alkane of the molecular formula C₅H₁₂ should contain three different types of H-atoms. Therefore, the isomer is n-pentane. It can be observed that there are three types of H atoms labelled as a, b and c in n-pentane.
Question 3
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The molecular formula C₅H₁₂ contains how many isomeric alkanes?

A
1

B
2

C
3

D
4

Solution

n-pentane, 2-ethylpropane, and 2-methylbutane are the 3 isomeric alkanes of C₅H₁₂ (pentane).
Question 4
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How many alcohols are structural isomers with the formula: C₅H₁₁OH?

A
5

B
6

C
7

D
8

Solution

Structural isomers of alcohol C₅H₁₁OH are as follow:-
Question 5
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A cyclic dichloride has a total five constitutional plus geometrical isomers. Which of the following satisfy this condition without altering the carbon skeleton?

A
Dichioromethyl cyclopropane

B
Dichlorocyclobutane

C
Dichlorocyclopentane

D
Dichlorocyclohexane

Solution

Only option b exists with 5 constitutional + geometrical isomers without altering carbon skeleton.
Question 6
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Which of the following carbonyls has four different enol isomers?

A
2-pentanone

B
Butanone

C
3-hexanone

D
2-methyl-3-pentanone

Solution

The given picture starts with an enol form of 3-hexanone.
Question 7
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How many different stereoisomers exist for 1-chloro-2-(3-chlorocyclobutyl) ethene?

A
2

B
4

C
5

D
7

Solution

So, there are 4 isomers of given compound.
Question 8
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Which of the following has three different stereoisomers?

A
1,3-butadiene

B
2,4-hexadiene

C
2,5-hexadiene

D
2,4-heptadiene

Solution

The correct answer is Option B.

CH₃−CH=CH−CH=CH−CH₃
2,4-hexadiene

Three different geometrical isomers of cis-cis, trans-trans and sic-trans are possible.
Question 9
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Which among the following does not exhibit geometric isomerism

A
1-hexene

B
2-hexene

C
3-hexene

D
4-hexene

Solution

Alkenes like 1-hexene when flipped from top to bottom they have identical structures and also they have C=CH2 unit which does not exist as cis- trans isomers.
Question 10
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'Which carbonyls below, on protonation gives a pair of stereoisomers?

A
Methanal

B
Acetone

C
Butanone

D
3-pentanone

Solution

The correct answer is option C
In chemistry, protonation (or hydronation) is the addition of a proton (or hydron, or hydrogen cation), (H+) to an atom, molecule, or ion, forming the conjugate acid. Some examples include. the protonation of water by sulfuric acid:
H₂SO₄ + H₂O ⇌ H₃O⁺ + HSO ⁻
Question 11
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A stereoisomer of cyclobutane-1,2-diol has lower solubility in water than its other stereoisomer. Which is this isomer and why?

A
Trans, lower dipole moment

B
Cis, higher dipole moment

C
Cis, intramolecular H-bonding

D
Trans, intramolecular H-bonding
Question 12
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How many cyclic isomers exists (structural and geometrical only) for C₃H₃CI₃?

A
2

B
3

C
4

D
5

Solution

These 3 are the possible structures.
Hence, B is correct.
Question 13
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which compound below can show geometrical isomerism ?

A

B

C

D

Solution

(a)
We have the same arrangement if the -CH₃and -H are interchanged. So, no GI.
(b)
Also in this compound we will get same arrangement across double bond if the positions of both -CH₃ are interchanged around a single bond
(c)
Same case here as in the above two.
(d)
Here, if we interchange -CH₃ and -H around a double bond, then we will get a different arrangement with respect to other double bond. So it shows GI.
Question 14
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Direction (Q. Nos. 14-17) This sectionis based on statement I and Statement II. Select the correct answer from the code given below
Q.
Statement I Fluoroethanal has two stereomeric enols in which cis enol predominates at equilibrium.
Statement II Intramolecular H-bonding increases the stability of a stereomer.

A
Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I

B
Both Statement I and Statement II are correct Statement II is not the correct explanation of Statement I

C
Statement I is correct but Statement II is incorrect

D
Statement II is correct but Statement I is incorrect
Question 15
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Q.
Statement I : Butanone, upon protonation at oxygen atom result in a pair of stereoisomer.
Statement II : Presence of lone pair of electrons at oxygen is responsible for protonation.

A
Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I

B
Both Statement I and Statement II are correct and Statement II is not the correct explanation of Statement I

C
Statement I is correct but Statement II is incorrect

D
Statement II is correct but Statement I is incorrect
Question 16
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Q.
Statement I : 1,2-dichlorocyclopropane has two stereoisomers.
Statement II : Restricted rotation is responsible for cis and trans-isomers of 1,2-dichlorocyclopropane.

A
Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I

B
Both Statement I and Statement II are correct and Statement II is not the correct explanation of Statement I

C
Statement I is correct but Statement II is incorrect

D
Statement II is correct but Statement I is incorrect

Solution

In order to show stereoisomers, a compound should not contain plain of symmetry,centre of symmetry,or any
In cis- form of this compound plain of symmetry will be present making the molecule incapable to show sterioisomerism
So statement 2 is correct, while statement 1 is incorrect.
Question 17
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Q.
Statement I : 1,2,3,4-tetrachloro-1,3-butadiene has two non-polar stereoisomers,
Statement II : Out of its four stereoisomers, two of them are polar.

A
Both Statement I and Statement II are correct and Statement II is the correct explanation of Statement I

B
Both Statement I and Statement II are correct and Statement II is not the correct explanation of Statement I

C
Statement I is correct but Statement II is incorrect

D
Statement II is correct but Statement I is incorrect