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Isomerism · Question 18

AIPMT 2014MCQMedium📈 Topic in 12% papers+4−1
1

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)

Answer

(3) (iv)

Solution

Racemisation is possible only when the substrate is optically active, i.e. the carbon bearing Cl is a chiral (asymmetric) carbon, and the reaction proceeds through a planar carbocation (SN1).

(i) C6H5CH2Cl, (ii) CH3CH2CH2Cl and (iii) (CH3)2CHCH2Cl: the carbon bearing Cl carries two H atoms ⇒ achiral ⇒ no racemisation.

(iv) 2-Chlorobutane: the carbon bearing Cl has four different groups (H, Cl, CH3, C2H5) ⇒ chiral.

As per NCERT, in SN1 hydrolysis of an optically active halide the planar carbocation is attacked from both faces ⇒ racemic mixture.

∴ Only (iv) undergoes racemisation.

Answer: (3)

AIPMT 2014

Keep practising — Isomerism

2

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
3

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)
4

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)
5

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)
6

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)
7

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

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
AIPMT 2010 (Mains)
8

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

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

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

  1. Butanol
  2. 2-Butyne
  3. 2-Butanol
  4. 2-Butene
AIPMT 2009
10

How many stereoisomers does this molecule have? CH3CH=CHCH2CHBrCH3

  1. 8
  2. 2
  3. 4
  4. 6
AIPMT 2008
11

CH3-CHCl-CH2-CH3 has a chiral centre. Which one of the following represents its R-configuration?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
AIPMT 2007

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