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Isomerism

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

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]

Answer

(2) [figure]

Solution

Priorities (CIP rules): Cl (1) > C2H5 (2) > CH3 (3) > H (4)

In a Fischer projection, if the lowest-priority group (H) is on a vertical bond, the sense of rotation 1 → 2 → 3 gives the configuration directly; if H is on a horizontal bond, the configuration is the reverse of what is seen.

(1) H horizontal; Cl (bottom) → C2H5 (top) → CH3 (right) appears clockwise ⇒ reversed ⇒ S

(2) H vertical (bottom); Cl (left) → C2H5 (top) → CH3 (right) is clockwise ⇒ R

(3) H horizontal; Cl (right) → C2H5 (bottom) → CH3 (top) is clockwise ⇒ reversed ⇒ S

(4) H vertical (bottom); Cl (right) → C2H5 (top) → CH3 (left) is anticlockwise ⇒ S

∴ Projection (2) represents the R-configuration.

Answer: (2)

Keep practising — Isomerism

Ques. 2AIPMT 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.
Ques. 3AIPMT 2006

Which of the following is not chiral?

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

The chirality of the compound [figure]

  1. R
  2. S
  3. E
  4. Z
Ques. 5AIPMT 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. 6AIPMT 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. 7AIPMT 2003

Which of the following pairs of compounds are enantiomers?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 8AIPMT 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. 9AIPMT 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. 10AIPMT 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. 11AIPMT 2001

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

  1. meso form
  2. racemic mixture
  3. d-form
  4. l-form

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