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Organic Chemistry – Some Basic Principles and Techniques · Question 10

NEET (UG) 2023MCQMedium📈 Topic in 25% papers+4−1
1

Consider the following compounds/species: [figure] The number of compounds/species which obey Hückel's rule is .

  1. 6
  2. 2
  3. 5
  4. 4

Answer

(4) 4

Solution

Hückel's rule: a cyclic, planar, fully conjugated species with (4n + 2) electrons is aromatic.

i. Naphthalene: 10 electrons (n = 2), obeys.

ii. Cyclopentadienyl anion: 6 electrons (n = 1), obeys.

iii. Cyclobutadiene: 4 electrons, antiaromatic, does not obey.

iv. Cyclopropenyl anion: 4 electrons, antiaromatic, does not obey.

v. Cyclopropenyl cation: 2 electrons (n = 0), obeys.

vi. Cyclooctatetraene: 8 electrons and non-planar (tub shaped), does not obey.

vii. Anthracene: 14 electrons (n = 3), obeys.

i, ii, v and vii obey Hückel's rule, i.e. 4.

Answer: (4)

NEET (UG) 2023

Keep practising — Organic Chemistry – Some Basic Principles and Techniques

2

Which compound amongst the following is not an aromatic compound?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET (UG) 2022
3

The correct IUPAC name of the following compound is [figure]

  1. 1-bromo-5-chloro-4-methylhexan-3-ol
  2. 6-bromo-2-chloro-4-methylhexan-4-ol
  3. 1-bromo-4-methyl-5-chlorohexan-3-ol
  4. 6-bromo-4-methyl-2-chlorohexan-4-ol
NEET (UG) 2022
4

What is the hybridization shown by C1 and C2 carbons, respectively in the given compound? OHC- 1CH=CH- 2CH2COOCH3

  1. sp3 and sp3
  2. sp2 and sp3
  3. sp2 and sp2
  4. sp3 and sp2
NEET (UG) 2022 (Phase 2)
5

Which of the following is the most stable carbocation?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET (UG) 2022 (Phase 2)
6

The correct structure of 2, 6-dimethyl-dec-4-ene is

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET (UG) 2021
7

A tertiary butyl carbocation is more stable than a secondary butyl carbocation because of which of the following?

  1. +R effect of -CH3 groups
  2. -R effect of -CH3 groups
  3. Hyperconjugation
  4. -I effect of -CH3 groups
NEET (UG) 2020
8

The number of sigma ( ) and pi ( ) bonds in pent-3-en-1-yne is -

  1. 11 bonds and 2 bonds
  2. 13 bonds and no bonds
  3. 10 bonds and 3 bonds
  4. 8 bonds and 5 bonds
NEET (UG) 2019
9

Which of the following is correct with respect to -I effect of the substituents? (R = alkyl)

  1. -NH2 < -OR < -F
  2. -NR2 < -OR < -F
  3. -NH2 > -OR > -F
  4. -NR2 > -OR > -F
NEET 2018
10

Which of the following carbocations is expected to be most stable?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET 2018
11

Which of the following molecules represents the order of hybridisation sp2, sp2, sp, sp from left to right atoms?

  1. HC C - C CH
  2. CH2 = CH - C CH
  3. CH2 = CH - CH = CH2
  4. CH3 - CH = CH - CH3
NEET 2018

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