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Organic Chemistry – Some Basic Principles and Techniques · Question 34

AIPMT 2015 (Cancelled)MCQMedium📈 Topic in 0% papers+4−1
1

Given : [figure] The enthalpy of hydrogenation of these compounds will be in the order as

  1. II > III > I
  2. II > I > III
  3. I > II > III
  4. III > II > I

Answer

(4) III > II > I

Solution

All three compounds take up 3 mol H2 and give the same product, 1,3,5-trimethylcyclohexane.

⇒ The less stable the starting compound, the more heat is released on hydrogenation.

I (mesitylene) is aromatic ⇒ large resonance stabilisation ⇒ most stable ⇒ least enthalpy of hydrogenation.

II has three conjugated C=C (non-aromatic) ⇒ some stabilisation by conjugation.

III has three isolated exocyclic C=C ⇒ no conjugation ⇒ least stable ⇒ largest enthalpy of hydrogenation.

∴ III > II > I

Answer: (4)

AIPMT 2015 (Cancelled)

Keep practising — Organic Chemistry – Some Basic Principles and Techniques

2

Which of the following organic compounds has same hybridization as its combustion product (CO2)?

  1. Ethane
  2. Ethyne
  3. Ethene
  4. Ethanol
AIPMT 2014
3

The radical, [figure] is aromatic because it has

  1. 7 p-orbitals and 7 unpaired electrons
  2. 6 p-orbitals and 7 unpaired electrons
  3. 6 p-orbitals and 6 unpaired electrons
  4. 7 p-orbitals and 6 unpaired electrons.
NEET 2013
4

The structure of isobutyl group in an organic compound is

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET 2013
5

Structure of the compound whose IUPAC name is 3-Ethyl-2-hydroxy-4-methylhex-3-en-5-ynoic acid is

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET 2013
6

The outer orbitals of C in ethene molecule can be considered to be hybridized to give three equivalent sp2 orbitals. The total number of sigma (σ) and pi (π) bonds in ethene molecule is

  1. 3 sigma (σ) and 2 pi (π) bonds
  2. 4 sigma (σ) and 1 pi (π) bonds
  3. 5 sigma (σ) and 1 pi (π) bonds
  4. 1 sigma (σ) and 2 pi (π) bonds
NEET 2013 (Karnataka)
7

Arrange the following in increasing order of stability 1. (CH3)2- C-CH2-CH3 2. (CH3)3- C 3. (CH3)2- CH 4. CH3- CH2 5. CH3

  1. 5 < 4 < 3 < 1 < 2
  2. 4 < 5 < 3 < 1 < 2
  3. 1 < 5 < 4 < 3 < 2
  4. 5 < 4 < 3 < 2 < 1
NEET 2013 (Karnataka)
8

What is the hybridisation state of benzyl carbonium ion? [figure]

  1. sp2
  2. spd2
  3. sp2d
  4. sp3
NEET 2013 (Karnataka)
9

Homolytic fission of the following alkanes forms free radicals CH3-CH3, CH3-CH2-CH3, (CH3)2CH-CH3, CH3-CH2-CH(CH3)2. Increasing order of stability of the radicals is

  1. (CH3)2 C-CH2CH3 < CH3- CH-CH3 < CH3- CH2 < (CH3)3 C
  2. CH3- CH2 < CH3- CH-CH3 < (CH3)2 C-CH2-CH3 < (CH3)3 C
  3. CH3- CH2 < CH3- CH-CH3 < (CH3)3 C < (CH3)2 C-CH2CH3
  4. (CH3)3 C < (CH3)2 C-CH2CH3 < CH3- CH-CH3 < CH3- CH2
NEET 2013 (Karnataka)
10

Which of the following chemical system is non aromatic?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET 2013 (Karnataka)
11

Which nomenclature is not according to IUPAC system?

  1. Br-CH2-CH=CH2 1-Bromoprop-2-ene
  2. [figure] 4-Bromo-2,4-dimethylhexane
  3. [figure] 2-Methyl-3-phenylpentane
  4. [figure] 5-Oxohexanoic acid
AIPMT 2012 (Prelims)

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