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Organic Chemistry – Some Basic Principles and Techniques · Question 36

NEET 2013MCQMedium📈 Topic in 25% papers+4−1
1

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.

Answer

(3) 6 p-orbitals and 6 unpaired electrons

Solution

The aromatic character of the radical comes from its benzene ring.

Each of the six ring carbon atoms is sp2 hybridised and has one unhybridised p-orbital containing one electron ⇒ 6 p-orbitals and 6 electrons.

These six electrons are delocalised over the planar, cyclic ring ⇒ (4n + 2) electrons with n = 1 (Hückel rule).

∴ As per NCERT's criteria of aromaticity (planarity, complete delocalisation, (4n + 2) electrons), the radical is aromatic because it has 6 p-orbitals and 6 unpaired electrons.

Answer: (3)

NEET 2013

Keep practising — Organic Chemistry – Some Basic Principles and Techniques

2

The structure of isobutyl group in an organic compound is

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

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]
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4

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)
5

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)
6

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

  1. sp2
  2. spd2
  3. sp2d
  4. sp3
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7

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
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8

Which of the following chemical system is non aromatic?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET 2013 (Karnataka)
9

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)
10

Which one of the following is most reactive towards electrophilic reagent?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
AIPMT 2011 (Prelims)
11

The correct IUPAC name for the compound is [figure]

  1. 4-ethyl-3-propylhex-1-ene
  2. 3-ethyl-4-ethenylheptane
  3. 3-ethyl-4-propylhex-5-ene
  4. 3-(1-ethylpropyl)hex-1-ene
AIPMT 2011 (Prelims)

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