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NEET CHEMISTRYHydrocarbonsMedium

Question

An alkene "A" on reaction with O3O_3 and Zn−H2OZn-H_2O gives propanone and ethanal in equimolar ratio. The addition of HCl to alkene "A" gives "B" as the major product. The structure of product "B" is:

A

(Option 1 Structure Missing)

B

(Option 2 Structure Missing)

C

4

D

(Option 4 Structure Missing)

Step-by-Step Solution

  1. Identify Alkene A (Reverse Ozonolysis): Ozonolysis cleaves the carbon-carbon double bond to form carbonyl compounds. To identify the starting alkene, remove the oxygen atoms from the products (Propanone and Ethanal) and join the carbonyl carbons with a double bond.
  • Products: Propanone [(CH3)2C=O(CH_3)_2C=O] and Ethanal [O=CHCH3O=CHCH_3].
  • Alkene A: 2-Methylbut-2-ene [(CH3)2C=CHCH3(CH_3)_2C=CHCH_3] .
  1. Reaction with HCl (Electrophilic Addition): The addition of HCl to the unsymmetrical alkene A follows Markovnikov's Rule.
  • Step 1 (Protonation): The proton (H+H^+) adds to the carbon with more hydrogen atoms (C−3C-3) to form the more stable carbocation. A tertiary (3∘3^\circ) carbocation is formed at C−2C-2 rather than a secondary one at C−3C-3 . (CH3)2C=CHCH3+H+→(CH3)2C+−CH2CH3(CH_3)_2C=CHCH_3 + H^+ \rightarrow (CH_3)_2C^+ -CH_2CH_3
  • Step 2 (Nucleophilic Attack): The chloride ion (Cl−Cl^-) attacks the stable tertiary carbocation. (CH3)2C+−CH2CH3+Cl−→(CH3)2C(Cl)CH2CH3(CH_3)_2C^+ -CH_2CH_3 + Cl^- \rightarrow (CH_3)_2C(Cl)CH_2CH_3
  1. Conclusion: The major product B is 2-Chloro-2-methylbutane.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Hydrocarbons. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYHydrocarbonsalkenereactionpropanoneethanalequimolar

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Phenylacetylene undergoes a reaction with dilute $\text{H}_2\text{SO}_4$ in the presence of $\text{HgSO}_4$ to yield:

A.Option 1 (Structure missing)
B.Option 2 (Structure missing)
C.Option 3 (Structure missing)
D.Option 4 (Structure missing)
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The reaction among the following that proceeds through an electrophilic substitution reaction is:

A.(Option 1 Structure Missing)
B.(Option 2 Structure Missing)
C.4
D.(Option 4 Structure Missing)
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The order of decreasing reactivity towards an electrophilic reagent for the following compounds is: (i) Benzene (ii) Toluene (iii) Chlorobenzene (iv) Phenol

A.(i) > (ii) > (iii) > (iv)
B.(ii) > (iv) > (i) > (iii)
C.(iv) > (iii) > (ii) > (i)
D.(iv) > (ii) > (i) > (iii)
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X and Y in the above-mentioned reaction are respectively:

A.X = 2–Butyne; Y = 3–Hexyne
B.X = 2-Butyne; Y = 2-Hexyne
C.X = 1-Butyne; Y = 2-Hexyne
D.X = 1-Butyne; Y = 3–Hexyne
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Match the bond line structures of hydrocarbons given in List-I with the corresponding boiling points given in List-II. List-II (Boiling point in K): (i) 300.9 (ii) 282.5 (iii) 309.1 (iv) 341.9 Choose the correct answer from the options given below:

A.(a)-(i), (b)-(iv), (c)-(iii), (d)-(ii)
B.(a)-(iii), (b)-(i), (c)-(iv), (d)-(ii)
C.(a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
D.(a)-(iv), (b)-(i), (c)-(ii), (d)-(iii)
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The dihedral angle of the least stable conformer of ethane is:

A.$60^{\circ}$
B.$0^{\circ}$
C.$120^{\circ}$
D.$180^{\circ}$
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Phenanthrene is an aromatic compound and follows Hückel's $(4n+2)\pi$ electron rule. The value of $n$ is:

A.0
B.1
C.2
D.3
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The correct statement regarding the comparison of staggered and eclipsed conformations of ethane is:

A.The eclipsed conformation of ethane is more stable than staggered conformation because eclipsed conformation has no torsional strain.
B.The eclipsed conformation of ethane is more stable than staggered conformation even though the eclipsed conformation has a torsional strain.
C.The staggered conformation of ethane is more stable than eclipsed conformation because staggered conformation has no torsional strain.
D.The staggered conformation of ethane is less stable than eclipsed conformation because staggered conformation has a torsional strain.
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