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Organic Chemistry – Some Basic Principles and Techniques

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

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)

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Ques. 2NEET (UG) 2022

Which compound amongst the following is not an aromatic compound?

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

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
Ques. 4NEET (UG) 2022 (Phase 2)

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
Ques. 5NEET (UG) 2022 (Phase 2)

Which of the following is the most stable carbocation?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 6NEET (UG) 2021

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

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
Ques. 7NEET (UG) 2020

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
Ques. 8NEET (UG) 2019

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
Ques. 9NEET 2018

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
Ques. 10NEET 2018

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

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

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

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