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Isomerism

AIPMT 2010 (Prelims)MCQEasyNot asked in last 5 yrs+4−1
Ques. 1AIPMT 2010 (Prelims)

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)

Keep practising — Isomerism

Ques. 2AIPMT 2009

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

  1. Butanol
  2. 2-Butyne
  3. 2-Butanol
  4. 2-Butene
Ques. 3AIPMT 2008

How many stereoisomers does this molecule have? CH3CH=CHCH2CHBrCH3

  1. 8
  2. 2
  3. 4
  4. 6
Ques. 4AIPMT 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]
Ques. 5AIPMT 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. 6AIPMT 2006

Which of the following is not chiral?

  1. 2-Hydroxypropanoic acid
  2. 2-Butanol
  3. 2,3-Dibromopentane
  4. 3-Bromopentane
Ques. 7AIPMT 2005

The chirality of the compound [figure]

  1. R
  2. S
  3. E
  4. Z
Ques. 8AIPMT 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. 9AIPMT 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. 10AIPMT 2003

Which of the following pairs of compounds are enantiomers?

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

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