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Organic Chemistry – Some Basic Principles and Techniques · Question 31

AIPMT 2015 (Cancelled)MCQMedium📈 Topic in 12% papers+4−1
1

Consider the following compounds : [figure] Hyperconjugation occurs in

  1. III only
  2. I and III
  3. I only
  4. II only

Answer

(1) III only

Solution

Hyperconjugation in a free radical needs an α-H, i.e. a C–H bond on a carbon directly attached to the radical carbon.

I: the radical carbon is attached to C(CH3)3 (quaternary carbon, no H) and to the benzene ring carbon (no H) ⇒ no α-H ⇒ no hyperconjugation (only resonance with the ring).

II: the radical carbon is attached to three phenyl groups ⇒ no α-H ⇒ no hyperconjugation.

III: the radical carbon is attached to the bridgehead CH and to the CH carrying CH3 ⇒ α-H present ⇒ hyperconjugation occurs.

∴ III only.

Answer: (1)

AIPMT 2015 (Cancelled)

Keep practising — Organic Chemistry – Some Basic Principles and Techniques

2

The enolic form of ethyl acetoacetate as shown below has [figure]

  1. 9 sigma bonds and 2 pi-bonds
  2. 9 sigma bonds and 1 pi-bond
  3. 18 sigma bonds and 2 pi-bonds
  4. 16 sigma bonds and 1 pi-bond.
AIPMT 2015 (Cancelled)
3

In which of the following compounds, the C–Cl bond ionisation shall give most stable carbonium ion?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
AIPMT 2015 (Cancelled)
4

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
AIPMT 2015 (Cancelled)
5

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

  1. Ethane
  2. Ethyne
  3. Ethene
  4. Ethanol
AIPMT 2014
6

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
7

The structure of isobutyl group in an organic compound is

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET 2013
8

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
9

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)
10

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)
11

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

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

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