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Organic Chemistry – Some Basic Principles and Techniques · Question 4

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1

Among the given compounds I-III, the correct order of bond dissociation energy of C-H bond marked with * is : [figure]

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

Answer

(3) II > I > III

Solution

Bond dissociation energy of a C–H bond increases with the s-character of the carbon and decreases when the radical formed is stabilised by resonance.

II: sp C–H of the alkyne (50% s-character) → shortest, strongest bond.

I: sp2 C–H of benzene (33% s-character); the phenyl radical formed is not resonance-stabilised.

III: sp3 C–H (25% s-character) of the CH2 next to the C=C (allylic); the radical formed is stabilised by the adjacent π bond → weakest bond.

∴ Order of bond dissociation energy: II > I > III

Answer: (3)

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2

The most stable carbocation among the following is :

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

A compound with a molecular formula of C6H14 has two tertiary carbons. Its IUPAC name is :

  1. n-hexane
  2. 2-methylpentane
  3. 2,3-dimethylbutane
  4. 2,2-dimethylbutane
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4

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

  1. 4-ethyl-1-fluoro-2-nitrobenzene
  2. 4-ethyl-1-fluoro-6-nitrobenzene
  3. 3-ethyl-6-fluoro-1-nitrobenzene
  4. 1-ethyl-4-fluoro-3-nitrobenzene
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5

Methyl group attached to a positively charged carbon atom stabilizes the carbocation due to

  1. -I inductive effect
  2. electromeric effect
  3. hyperconjugation
  4. mesomeric effect
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6

The number of bonds, bonds and lone pair of electrons in pyridine, respectively are:

  1. 12, 3, 0
  2. 11, 3, 1
  3. 12, 2, 1
  4. 11, 2, 0
NEET (UG) 2023
7

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
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8

Which compound amongst the following is not an aromatic compound?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
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9

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
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10

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
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11

Which of the following is the most stable carbocation?

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