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Organic Chemistry – Some Basic Principles and Techniques · Question 19

NEET 2018MCQHard📈 Topic in 38% papers+4−1
1

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

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

Answer

(3) [figure]

Solution

In each cation the positive charge is delocalised by resonance over the three carbons ortho and para to the sp3 (C–H, Y) carbon.

-NO2 is a strong electron-withdrawing group (−I, −R) ⇒ a positive charge on the carbon carrying -NO2 is strongly destabilised.

(1), (2), (4): -NO2 is ortho/para to the sp3 carbon ⇒ one resonance structure places on the carbon bearing -NO2 ⇒ destabilised.

(3): -NO2 is meta to the sp3 carbon ⇒ never comes on the carbon bearing -NO2 ⇒ least destabilised.

∴ Cation (3) is the most stable.

Answer: (3)

NEET 2018

Keep practising — Organic Chemistry – Some Basic Principles and Techniques

2

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
3

The correct statement regarding electrophile is

  1. electrophile is a negatively charged species and form a bond by accepting a pair of electrons from another electrophile
  2. electrophiles are generally neutral species and can form a bond by accepting a pair of electrons from a nucleophile
  3. electrophile can be either neutral or positively charged species and can form a bond by accepting a pair of electrons from a nucleophile
  4. electrophile is a negatively charged species and can form a bond by accepting a pair of electrons from a nucleophile.
NEET 2017
4

The IUPAC name of the compound [figure]

  1. 5-formylhex-2-en-3-one
  2. 5-methyl-4-oxohex-2-en-5-al
  3. 3-keto-2-methylhex-5-enal
  4. 3-keto-2-methylhex-4-enal
NEET 2017
5

Which one is the correct order of acidity?

  1. CH CH > CH3-C CH > CH2=CH2 > CH3-CH3
  2. CH CH > CH2=CH2 > CH3-C CH > CH3-CH3
  3. CH3-CH3 > CH2=CH2 > CH3-C CH > CH CH
  4. CH2=CH2 > CH3-CH=CH2 > CH3-C CH > CH CH
NEET 2017
6

For the following reactions : (A) CH3CH2CH2Br + KOH CH3CH=CH2 + KBr + H2O (B) [figure] (C) [figure] Which of the following statements is correct?

  1. (A) is elimination, (B) and (C) are substitution reactions.
  2. (A) is substitution, (B) and (C) are addition reactions.
  3. (A) and (B) are elimination reactions and (C) is addition reaction.
  4. (A) is elimination, (B) is substitution and (C) is addition reaction.
NEET 2016 (Phase 1)
7

The pair of electrons in the given carbanion, CH3C C-, is present in which of the following orbitals?

  1. sp2
  2. sp
  3. 2p
  4. sp3
NEET 2016 (Phase 1)
8

In which of the following molecules, atoms are coplanar?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
NEET 2016 (Phase 2)
9

In pyrrole the electron density is maximum on [figure]

  1. 2 and 3
  2. 3 and 4
  3. 2 and 4
  4. 2 and 5
NEET 2016 (Phase 2)
10

Which of the following statements is not correct for a nucleophile?

  1. Ammonia is a nucleophile.
  2. Nucleophiles attack low e- density sites.
  3. Nucleophiles are not electron seeking.
  4. Nucleophile is a Lewis acid.
AIPMT 2015
11

The total number of π-bond electrons in the following structure is [figure]

  1. 12
  2. 16
  3. 4
  4. 8
AIPMT 2015 (Cancelled)

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