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Isomerism · Question 6

NEET (UG) 2022MCQEasy📈 Topic in 12% papers+4−1
1

The incorrect statement regarding chirality is

  1. SN1 reaction yields 1 : 1 mixture of both enantiomers
  2. The product obtained by SN2 reaction of haloalkane having chirality at the reactive site shows inversion of configuration
  3. Enantiomers are superimposable mirror images on each other
  4. A racemic mixture shows zero optical rotation

Answer

(3) Enantiomers are superimposable mirror images on each other

Solution

(1) As per NCERT, in an SN1 reaction the planar carbocation is attacked from both faces, so a chiral substrate gives a 1 : 1 mixture of the two enantiomers (racemisation). Correct.

(2) In an SN2 reaction the nucleophile attacks from the side opposite to the leaving group, so the product shows inversion of configuration. Correct.

(3) Enantiomers are non-superimposable mirror images of each other. Hence the statement is incorrect.

(4) In a racemic mixture the rotation by one enantiomer is cancelled by the other ⇒ net optical rotation is zero. Correct.

Answer: (3)

NEET (UG) 2022

Keep practising — Isomerism

2

The compound which shows metamerism is :

  1. C4H10O
  2. C5H12
  3. C3H8O
  4. C3H6O
NEET (UG) 2021
3

Dihedral angle of least stable conformer of ethane is :

  1. 0
  2. 120
  3. 180
  4. 60
NEET (UG) 2021
4

With respect to the conformers of ethane, which of the following statements is true?

  1. Bond angle changes but bond length remains same.
  2. Both bond angle and bond length change.
  3. Both bond angle and bond length remain same.
  4. Bond angle remains same but bond length changes.
NEET 2017
5

Which of the following biphenyls is optically active ?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET 2016 (Phase 1)
6

The correct statement regarding the comparison of staggered and eclipsed conformations of ethane, is

  1. the eclipsed conformation of ethane is more stable than staggered conformation even though the eclipsed conformation has torsional strain
  2. the staggered conformation of ethane is more stable than eclipsed conformation, because staggered conformation has no torsional strain
  3. the staggered conformation of ethane is less stable than eclipsed conformation, because staggered conformation has torsional strain
  4. the eclipsed conformation of ethane is more stable than staggered conformation, because eclipsed conformation has no torsional strain.
NEET 2016 (Phase 1)
7

The correct statement regarding a carbonyl compound with a hydrogen atom on its alpha-carbon, is

  1. a carbonyl compound with a hydrogen atom on its alpha-carbon rapidly equilibrates with its corresponding enol and this process is known as carbonylation
  2. a carbonyl compound with a hydrogen atom on its alpha-carbon rapidly equilibrates with its corresponding enol and this process is known as keto-enol tautomerism
  3. a carbonyl compound with a hydrogen atom on its alpha-carbon never equilibrates with its corresponding enol
  4. a carbonyl compound with a hydrogen atom on its alpha-carbon rapidly equilibrates with its corresponding enol and this process is known as aldehyde-ketone equilibration.
NEET 2016 (Phase 1)
8

Which among the given molecules can exhibit tautomerism? [figure]

  1. III only
  2. Both I and III
  3. Both I and II
  4. Both II and III
NEET 2016 (Phase 2)
9

The possible stereo-structures of CH3CHOHCOOH, which are optically active, are called

  1. atropisomers
  2. enantiomers
  3. mesomers
  4. diastereomers
AIPMT 2015
10

In an SN1 reaction on chiral centers, there is

  1. inversion more than retention leading to partial racemisation
  2. 100% retention
  3. 100% inversion
  4. 100% racemisation
AIPMT 2015
11

The number of structural isomers possible from the molecular formula C3H9N is

  1. 5
  2. 2
  3. 3
  4. 4
AIPMT 2015

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