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Hydrocarbons · Question 24

JEE Main 2025 (Online) 7th April Evening ShiftNumericalMedium📈 Topic in 26% papers+4
1

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 .

Answer

7

Solution

Step 1: PCl5 replaces the carbonyl oxygen by two Cl atoms (gem-dichloride):

A = Ph-CCl2-CH3

Step 2: Two equivalents of NaNH2 remove two molecules of HCl (double dehydrohalogenation) giving phenylacetylene; the third equivalent removes the acidic terminal H:

B = Ph-C C Na (sodium phenylacetylide)

Step 3: Acidification gives back the terminal alkyne:

C = Ph-C CH (phenylethyne)

Step 4: Hydroboration–oxidation of a terminal alkyne adds H and OH anti-Markovnikov; the enol formed tautomerises to an aldehyde:

D = Ph-CH2-CHO (phenylacetaldehyde) [figure]

sp2 carbons in D: 6 (benzene ring) + 1 (CHO carbon) = 7; the CH2 carbon is sp3.

Answer: 7

JEE Main 2025 (Online) 7th April Evening Shift

Keep practising — Hydrocarbons

2

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
3

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
4

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
5

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
6

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
7

A molecule (P) on treatment with acid undergoes rearrangement and gives (Q). (Q) on ozonolysis followed by reflux under alkaline condition gives (R). The structure of (R) is given below. [figure] The structure of (P) is

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
JEE Main 2025 (Online) 28th January Morning Shift
8

Identify product [A], [B] and [C] in the following reaction sequence. CH3-C CH [H2]Pd/C [A] [(ii) Zn, H2O](i) O3 [B] + [C]

  1. [A]: CH3-CH=CH2, [B]: CH3CHO, [C]: CH3CH2OH
  2. [A]: CH3-CH=CH2, [B]: CH3CHO, [C]: HCHO
  3. [A]: CH3CH2CH3, [B]: CH3CHO, [C]: HCHO
  4. [A]: CH2=CH2, [B]: H3C- O \|C-CH3, [C]: HCHO
JEE Main 2025 (Online) 28th January Evening Shift

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