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Hydrocarbons · Question 19

JEE Main 2026 (Online) 22nd January Evening ShiftMCQHard📈 Topic in 3% papers+4−1
1

The dibromo compound [P] (molecular formula: C9H10Br2) when heated with excess sodamide followed by treatment with dilute HCl gives [Q]. On warming [Q] with mercuric sulphate and dilute sulphuric acid yields [R] which gives positive Iodoform test but negative Tollens' test. The compound [P] is :

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

Answer

(4) [figure]

Solution

[R]: positive iodoform test and negative Tollens' test R is a methyl ketone, Ar-CO-CH3.

[R] is formed by hydration ( Hg2+/H+) of [Q] Q is a terminal alkyne Ar-C CH (Markovnikov addition gives the methyl ketone).

[Q] is formed from [P] by double dehydrobromination with excess NaNH2 (the terminal alkyne is first obtained as its sodium salt; dilute HCl regenerates it) both Br atoms of P are on the two side-chain carbons.

Double bond equivalent of C9H10Br2 (treat Br as H, C9H12) = 9 - 122 + 1 = 4 benzene ring.

P = 1-(1,1-dibromoethyl)-4-methylbenzene (option D):

CH3C6H4CBr2CH3 [(ii) dil. HCl](i) excess NaNH2, CH3C6H4C CH (Q)

CH3C6H4C CH + H2O [dil. H2SO4]HgSO4 CH3C6H4COCH3 (R)

R (4-methylacetophenone) has a CH3CO- group iodoform test positive; it is a ketone Tollens' test negative.

Other options:

(A) the carbon carrying Ph, CH3 and Br cannot become a C≡C carbon no alkyne.

(B) the two CH2Br groups are on different ring carbons no C≡C can form.

(C) -C(Br)=CHBr can lose only one HBr, giving a bromoalkyne, not a terminal alkyne; its ring is also not aromatic.

Answer: (4)

JEE Main 2026 (Online) 22nd January Evening Shift

Keep practising — Hydrocarbons

2

Identify A in the following reaction. [figure]

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
JEE Main 2026 (Online) 21st January Morning Shift
3

[figure] 'P' is

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
JEE Main 2025 (Online) 8th April Evening Shift
4

Choose the correct set of reagents for the following conversion. [figure]

  1. Cl2/ anhy. AlCl3; Br2/Fe; alc. KOH
  2. Cl2/Fe; Br2/ anhy. AlCl3; aq. KOH
  3. Br2/Fe; Cl2, ; alc. KOH
  4. Br2/ anhy. AlCl3; Cl2, ; aq. KOH
JEE Main 2025 (Online) 8th April Evening Shift
5

Given below are two statements: In the light of the above statements, choose the correct answer from the options given below

  1. Statement I is false but Statement II is true
  2. Both Statement I and Statement II are false
  3. Statement I is true but Statement II is false
  4. Both Statement I and Statement II are true
JEE Main 2025 (Online) 7th April Morning Shift
6

Identify the structure of the final product (D) in the following sequence of the reactions : [figure] Total number of sp2 hybridised carbon atoms in product D is .

JEE Main 2025 (Online) 7th April Evening Shift
7

Predict the major product of the following reaction sequence: [figure]

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
JEE Main 2025 (Online) 4th April Morning Shift
8

Consider the following molecule(X). [figure] The major product formed when the given molecule (X) is treated with HBr (1 eq) is :

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
JEE Main 2025 (Online) 4th April Evening Shift
9

Which compound would give 3-methyl-6-oxoheptanal upon ozonolysis?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
JEE Main 2025 (Online) 3rd April Morning Shift
10

An optically active alkyl halide C4H9Br [A] reacts with hot KOH dissolved in ethanol and forms alkene [B] as major product which reacts with bromine to give dibromide [C]. The compound [C] is converted into a gas [D] upon reacting with alcoholic NaNH2. During hydration 18 gram of water is added to 1 mole of gas [D] on warming with mercuric sulphate and dilute acid at 333 K to form compound [E]. The IUPAC name of compound [E] is :

  1. Butan-2-ol
  2. But-2-yne
  3. Butan-2-one
  4. Butan-1-al
JEE Main 2025 (Online) 2nd April Morning Shift
11

Given below are two statements: In the light of the above statements, choose the most appropriate answer from the options given below:

  1. Statement I is incorrect but Statement II is correct
  2. Both Statement I and Statement II are correct
  3. Statement I is correct but Statement II is incorrect
  4. Both Statement I and Statement II are incorrect
JEE Main 2025 (Online) 2nd April Evening Shift

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