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Isomerism

AIPMT 2007MCQMediumNot asked in last 5 yrs+4−1
Ques. 1AIPMT 2007

If there is no rotation of plane polarised light by a compound in a specific solvent, though thought to be chiral, it may mean that

  1. the compound is certainly meso
  2. there is no compound in the solvent
  3. the compound may be a racemic mixture
  4. the compound is certainly achiral.

Answer

(1) the compound is certainly meso

Solution

A compound containing chiral carbon atoms is expected to be optically active.

∵ In a meso compound the molecule has a plane of symmetry; the rotation caused by one half of the molecule is exactly cancelled by the other half (internal compensation).

⇒ The compound shows no rotation of plane polarised light even though it contains chiral centres, e.g. meso-tartaric acid.

As per NCERT, a racemic mixture also shows zero optical rotation, but it is an equimolar mixture of two enantiomers (external compensation), not a single compound.

∴ The single compound showing no rotation is a meso compound.

Answer: (1)

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Ques. 2AIPMT 2006

Which of the following is not chiral?

  1. 2-Hydroxypropanoic acid
  2. 2-Butanol
  3. 2,3-Dibromopentane
  4. 3-Bromopentane
Ques. 3AIPMT 2005

The chirality of the compound [figure]

  1. R
  2. S
  3. E
  4. Z
Ques. 4AIPMT 2005

Which one of the following pairs represents stereoisomerism?

  1. Structural isomerism and geometrical isomerism
  2. Optical isomerism and geometrical isomerism
  3. Chain isomerism and rotational isomerism
  4. Linkage isomerism and geometrical isomerism.
Ques. 5AIPMT 2004

The molecular formula of diphenylmethane, [figure] is C13H12. How many structural isomers are possible when one of the hydrogens is replaced by a chlorine atom?

  1. 6
  2. 4
  3. 8
  4. 7
Ques. 6AIPMT 2003

Which of the following pairs of compounds are enantiomers?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 7AIPMT 2003

In this reaction : CH3CHO + HCN CH3CH(OH)CN HOH CH3CH(OH)COOH an asymmetric centre is generated. The acid obtained would be

  1. D-isomer
  2. L-isomer
  3. 50% D + 50% L-isomer
  4. 20% D + 80% L-isomer
Ques. 8AIPMT 2002

Geometrical isomers differ in

  1. position of functional group
  2. position of atoms
  3. spatial arrangement of atoms
  4. length of carbon chain
Ques. 9AIPMT 2001

A compound of molecular formula C7H16 shows optical isomerism, compound will be

  1. 2,3-dimethylpentane
  2. 2,2-dimethylbutane
  3. 2-methylhexane
  4. none of these
Ques. 10AIPMT 2001

[figure] obtained by chlorination of n-butane will be

  1. meso form
  2. racemic mixture
  3. d-form
  4. l-form
Ques. 11AIPMT 2000

2-Butene shows geometrical isomerism due to

  1. restricted rotation about double bond
  2. free rotation about double bond
  3. free rotation about single bond
  4. chiral carbon

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