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Isomerism · Question 25

AIPMT 2010 (Prelims)MCQEasy📈 Topic in 0% papers+4−1
1

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

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

Answer

(2) [figure]

Solution

Option (1) is the gauche (skew) form: the two CH3 groups are at 60 and repel each other.

Options (3) and (4) are eclipsed forms with maximum torsional strain; (3), with CH3 eclipsing CH3, is the least stable.

Option (2) is the anti (staggered) form: the two CH3 groups are at 180 , so torsional and steric strain are minimum.

The anti conformation (2) is the most stable.

Answer: (2)

AIPMT 2010 (Prelims)

Keep practising — Isomerism

2

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

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

How many stereoisomers does this molecule have? CH3CH=CHCH2CHBrCH3

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

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
5

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
6

Which of the following is not chiral?

  1. 2-Hydroxypropanoic acid
  2. 2-Butanol
  3. 2,3-Dibromopentane
  4. 3-Bromopentane
AIPMT 2006
7

The chirality of the compound [figure]

  1. R
  2. S
  3. E
  4. Z
AIPMT 2005
8

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
9

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
10

Which of the following pairs of compounds are enantiomers?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
AIPMT 2003
11

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

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