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Isomerism · Question 17

AIPMT 2015 (Cancelled)MCQHard📈 Topic in 0% papers+4−1
1

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

Answer

(2) I, II and III

Solution

Keto–enol tautomerism needs a hydrogen that can shift to the carbonyl oxygen: an α-H, or in an α,β-unsaturated ketone also a γ-H (through the conjugated C=C–C=O system).

Number the ring: C-1 = C=O, C-2=C-3 double bond.

I: C-6 is a CH2 group next to C=O ⇒ α-H present ⇒ enolises.

II: C-6 is a CH2 group ⇒ α-H present ⇒ enolises.

III: C-6 carries two CH3 groups (no α-H there), but C-4 (CH2) is the γ-carbon of the conjugated enone ⇒ its H can shift to O through the C=C–C=O system to give a dienol ⇒ tautomerism possible.

∴ All three, I, II and III, can show tautomerism.

Answer: (2)

AIPMT 2015 (Cancelled)

Keep practising — Isomerism

2

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)
AIPMT 2014
3

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
NEET 2013
4

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
NEET 2013 (Karnataka)
5

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

  1. three
  2. four
  3. five
  4. two
NEET 2013 (Karnataka)
6

Which of the following acids does not exhibit optical isomerism?

  1. Maleic acid
  2. -amino acids
  3. Lactic acid
  4. Tartaric acid
AIPMT 2012 (Prelims)
7

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
AIPMT 2011 (Mains)
8

Which of the following conformers for ethylene glycol is most stable?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
AIPMT 2010 (Mains)
9

In the following the most stable conformation of n-butane is

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
AIPMT 2010 (Prelims)
10

Which of the following compounds will exhibit cis-trans (geometrical) isomerism?

  1. Butanol
  2. 2-Butyne
  3. 2-Butanol
  4. 2-Butene
AIPMT 2009
11

How many stereoisomers does this molecule have? CH3CH=CHCH2CHBrCH3

  1. 8
  2. 2
  3. 4
  4. 6
AIPMT 2008

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