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Isomerism (GATE)

Description: GAte
Number of Questions: 15
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Tags: GAte Optical and Geometrical Isomerism
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Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option.

Assertion: The energy difference between staggered and eclipsed conformations of ethylene dichloride is less than in ethylene dibromide. Reason: The bond moment of C-Cl is greater than that of C-Br.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: B
Explanation:

This option is correct. Due to steric hindrance between big-sized Br atoms, the energy difference between staggered and eclipsed forms of ethylene dibromide is more.

Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option.

Assertion: The compound C6H5CH=CHCl is called β-chlorostyrene. Reason: In organic halides, the carbon atom is attached to the halogen atom designated as α.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: B
Explanation:

This option is correct because in styrene, carbon atom attached to phenyl group is designated as α-carbon, while that carrying Cl-atom is designated as β-carbon.

Which of the following statements is/are correct?

A. 1-Chloro-2,3-pentadiene has no chiral carbon atoms, yet it is a chiral molecule. B. A newly discovered compound is through to be chiral, but shows no rotation in a specific solvent. This means that the compound is assuredly achiral. C. When a chiral molecule reacts to give a chiral molecule, the product is always racemic.

  1. Only A

  2. Only B

  3. Only C

  4. A and C

  5. B and C

Show answer
Correct Option: A
Explanation:

This statement is correct because the molecule as whole is chiral since this molecule and its mirror image are non-superimposable.

Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option. Assertion: Cyclohexane floats over water. Reason: Most of the molecules of cyclohexane assume boat conformation.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: C
Explanation:

This option is correct. Assertion is correct because cyclohexane floats over water because the density of cyclohexane is lower than that of water.

Which of the following statements is/are wrong?

A. 1-Methoxypropane and 2-methoxypropane are metamers. B. An optically active substance must be achiral. C. m-Chlorobromobenzene and m-bromochlorobenzene are isomers.

  1. A and B

  2. A and C

  3. B and C

  4. A, B and C

  5. Only A

Show answer
Correct Option: D
Explanation:

Statements A, B and C are incorrect. 1-Methoxypropane and 2-methoxypropane are positional isomers , an optically active substance must be chiral and  Isomers are molecules that have the same molecular formula, but have a different arrangement of the atoms in space.

Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option.

Assertion: In CH2F2, the F-C-F bond angle is less than 109.5˚, indicating less than 25% s-character, but the H-C-H bond angle is larger and the C-H bond has more s-character. Reason: More electronegative substituents prefer hybrid orbitals having less s-character and more electropositive substituents prefer hybrid orbitals having more s-character.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: A
Explanation:

This option is correct because according to bent rule, more electronegative substituents prefer hybrid orbitals having less s-character and more electropositive substituents prefer hybrid orbitals having more s-character. 

Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option. Assertion: Benzaldehyde forms two oximes on reacting with NH2OH. Reason: The two oximes arise due to geometrical isomerism around C=N bond.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: A
Explanation:

Benzaldehyde forms two oximes on reacting with NH2OH because the two oximes arise due to geometrical isomerism around C=N bond. Thus, this option is correct.

Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option. Assertion: 1,2-Propadiene exhibits optical isomerism. Reason: Its mirror image is non-superimposable.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: E
Explanation:

This option is correct because 1,2-propadiene does not exhibit optical isomerism and it contains an axis of symmetry.

Which of the following statements is/are false?

A. Compounds containing one chiral carbon atom are always optically active. B. Maleic acid and fumeric acid are geometrical isomers. C. Maleic acid is less soluble in water than fumeric acid.

  1. Only A

  2. Only B

  3. Only C

  4. A, B and C

  5. A and B

Show answer
Correct Option: C
Explanation:

This option is correct because maleic acid, being a cis-isomer, is less closely packed in the crystal lattice as compared to fumeric acid (trans isomer) and hence, is more soluble in water than fumeric acid.

Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option.

Assertion: Propionic acid contains a prochiral carbon. Reason: Replacement of hydrogen atom of the CH2 group by Br atom produces achiral carbon.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: A
Explanation:

Correct answer. Propionic acid contains a prochiral carbon because replacement of hydrogen atom of the CH2 group by Br atom produces achiral carbon.

Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option.

Assertion: CHBr = CHCl exhibits geometrical isomerism, but CH2Br-CH2Cl does not. Reason: Presence of C=C is one of the conditions of geometrical isomerism.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: B
Explanation:

Reason statement about the conditions of geometrical isomers is correct but this is not correct explanation of assertion statement.There must be two different side groups joined to the C=C on both sides is another condition for geometrical isomerism. 

Which of the following statements is/are true?

A. The dihedral angle between the H-atoms in staggered conformation of ethane is 60˚. B. C2H5O2N shows functional isomerism as well as tautomerism. C. Cyclopropane is a better fuel than propane.

  1. Only A

  2. Only B

  3. A and C

  4. A, B and C

  5. Only C

Show answer
Correct Option: D
Explanation:

This option is correct because dihedral angle between the H-atoms in staggered conformation of ethane is 60˚. 

Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option.

Assertion: Stereoisomers, which are not mirror images of each other, are called diastereomers. Reason: Diastereomers may or may not be optically active.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: B
Explanation:

Diastereomers may or may not be chiral and hence, they may or may not be optically active. This property helps to separate out products formed during organic reactions.

Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option. Assertion: Both cyclopropane and propene give addition reactions readily. Reason: Cyclopropane and propene are isomers of each other.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: B
Explanation:

This option is correct because propene, being unsaturated, undergoes addition reaction.

Directions: In the question given below, there are two statements labelled Assertion (A) and Reason (R). Choose the correct option.

Assertion: All the carbon atoms in but-2-ene lie in one plane. Reason: All the carbon atoms of but-2-ene are sp2-hybridised.

  1. Both A and R are true and R is the correct explanation of A.

  2. Both A and R are true, but R is not the correct explanation of A.

  3. A is true, but R is false.

  4. A is false, but R is true.

  5. Both A and R are false.

Show answer
Correct Option: C
Explanation:

All the carbon atoms in but-2-ene lie in one plane.  In but - 2 - ene terminal carbon atoms are sp3 hybridised.

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