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Isomerism · Question 28

AIPMT 2007MCQMedium📈 Topic in 0% papers+4−1
1

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)

AIPMT 2007

Keep practising — Isomerism

2

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.
AIPMT 2007
3

Which of the following is not chiral?

  1. 2-Hydroxypropanoic acid
  2. 2-Butanol
  3. 2,3-Dibromopentane
  4. 3-Bromopentane
AIPMT 2006
4

The chirality of the compound [figure]

  1. R
  2. S
  3. E
  4. Z
AIPMT 2005
5

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.
AIPMT 2005
6

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
AIPMT 2004
7

Which of the following pairs of compounds are enantiomers?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
AIPMT 2003
8

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
AIPMT 2003
9

Geometrical isomers differ in

  1. position of functional group
  2. position of atoms
  3. spatial arrangement of atoms
  4. length of carbon chain
AIPMT 2002
10

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
AIPMT 2001
11

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

  1. meso form
  2. racemic mixture
  3. d-form
  4. l-form
AIPMT 2001

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