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Isomerism

NEET 2016 (Phase 2)MCQHardNot asked in last 5 yrs+4−1
Ques. 1NEET 2016 (Phase 2)

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

Answer

(1) III only

Solution

Keto–enol tautomerism needs an α-H atom that can shift to O to form a C=C (enol).

I: both α-carbons are bridgehead carbons ⇒ a C=C at a bridgehead of this small bicyclic ring is too strained (Bredt's rule) ⇒ no enol.

II: one α-carbon is a bridgehead (no enol possible) and the other carries two Ph groups (no α-H) ⇒ no enol.

III: the α-CH2 group has α-H atoms ⇒ enol is formed ⇒ tautomerism.

∴ III only.

Answer: (1)

Keep practising — Isomerism

Ques. 2AIPMT 2015

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

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

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
Ques. 4AIPMT 2015

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

  1. 5
  2. 2
  3. 3
  4. 4
Ques. 5AIPMT 2015 (Cancelled)

Given : [figure] Which of the given compounds can exhibit tautomerism?

  1. II and III
  2. I, II and III
  3. I and II
  4. I and III
Ques. 6AIPMT 2014

Which of the following compounds will undergo racemisation when solution of KOH hydrolyses? [figure]

  1. (i) and (ii)
  2. (ii) and (iv)
  3. (iv)
  4. (i) and (iv)
Ques. 7NEET 2013

The order of stability of the following tautomeric compounds is [figure]

  1. II > I > III
  2. II > III > I
  3. I > II > III
  4. III > II > I
Ques. 8NEET 2013 (Karnataka)

Given: [figure] I and II are

  1. identical
  2. a pair of conformers
  3. a pair of geometrical isomers
  4. a pair of optical isomers
Ques. 9NEET 2013 (Karnataka)

Number of isomeric alcohols of molecular formula C6H14O which give positive iodoform test is

  1. three
  2. four
  3. five
  4. two
Ques. 10AIPMT 2012 (Prelims)

Which of the following acids does not exhibit optical isomerism?

  1. Maleic acid
  2. -amino acids
  3. Lactic acid
  4. Tartaric acid
Ques. 11AIPMT 2011 (Mains)

The IUPAC name of the following compound is [figure]

  1. trans-2-chloro-3-iodo-2-pentene
  2. cis-3-iodo-4-chloro-3-pentene
  3. trans-3-iodo-4-chloro-3-pentene
  4. cis-2-chloro-3-iodo-2-pentene

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