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Predict the major product of the following reaction sequence:
Alkyl radical halogenation flowchart matrix for Q42 - JEE Main 2025 Morning
The sequence pathways specify Br2/hv free radical substitution, alcoholic KOH elimination, and HBr/peroxide addition.

Solution & Explanation

### Core Logic Let's analyze the steps of the reaction sequence: 1. **Step 1 (Br_2 / hnu):** Light-induced free radical substitution targeted at the most stable tertiary position, producing 1-bromo-1-methylcyclohexane. 2. **Step 2 (Alcoholic KOH, Delta):** Dehydrohalogenation occurs via an E2 mechanism. Following Saytzeff's rule, elimination favors the formation of the more highly substituted, stable alkene: 1-methylcyclohexene. 3. **Step 3 (HBr / R-O-O-R, hnu):** Radical hydrobromination across the unsymmetrical alkene. The presence of peroxide shifts addition toward the **Anti-Markovnikov** path, placing the bromine atom cleanly at the less-substituted secondary carbon to yield **1-bromo-2-methylcyclohexane**. ### Pattern Recognition Combining Saytzeff elimination with a peroxide-promoted HBr addition allows you to reposition functional groups from highly substituted tertiary carbons to adjacent secondary positions. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Hydrocarbons Class 12 Chemistry: Haloalkanes and Haloarenes
Detailed mechanism scheme tracing intermediates for Q42
The sequence pathways specify Br2/hv free radical substitution, alcoholic KOH elimination, and HBr/peroxide addition.

Reference Study Guides

More Hydrocarbons Previous-Year Questions — Page 3

Q27 2025 Electrophilic Addition to Alkenes
Following are the four molecules "P", "Q", "R" and "S":
Electrophilic Addition to Alkenes diagram for Q27 - JEE Main 2025 Morning
The image shows four cyclic and acyclic alkene molecules labelled P, Q, R, and S.
Which one among the four molecules will react with H-Br(aq) at the fastest rate?
  • A. S
  • B. Q
  • C. R
  • D. P

Solution

### Related Formula textRate of Electrophilic Addition propto textStability of Intermediate Carbocation ### Core Logic Addition of H-Br(aq) follows an electrophilic addition pathway where a carbocation intermediate is formed in the rate-determining step. Among the given structures, compound Q forms a resonance-stabilized allylic/benzylic carbocation, rendering it highly stable compared to the others.
Electrophilic Addition to Alkenes solution diagram for Q27 - JEE Main 2025 Morning
The image shows four cyclic and acyclic alkene molecules labelled P, Q, R, and S.
### Pattern Recognition Look for conjugated or allylic systems that stabilize the positive charge dynamically via resonance. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Hydrocarbons
Q29 2025 Alkyne Reactions and Ozonolysis
Identify product [A], [B] and [C] in the following reaction sequence : CH_3-Cequiv CHfracPd/CH_2rightarrow[A]frac(i)O_3(ii)Zn,H_2Orightarrow[B]+[C]
  • A. [A]:CH_3-CH=CH_2,\ [B]: CH_3CHO,\ [C]: HCHO
  • B. [A]: CH_2=CH_2,\ [B]: H_3C-CO-CH_3,\ [C]: HCHO
  • C. [A]:CH_3-CH=CH_2,\ [B]: CH_3CHO,\ [C]: CH_3CH_2OH
  • D. [A]: CH_3CH_2CH_3,\ [B]: CH_3CHO,\ [C]: HCHO

Solution

### Related Formula Partial hydrogenation of alkynes using Pd/C yields alkenes: R-Cequiv CH + H_2 xrightarrowPd/C R-CH=CH_2 Ozonolysis cleaves the double bond to form carbonyls: R-CH=CH_2 xrightarrow(i)O_3, (ii)Zn/H_2O R-CHO + HCHO ### Core Logic Step 1: Controlled reduction of propyne gives propene: CH_3-Cequiv CH xrightarrowPd/C, H_2 CH_3-CH=CH_2 quad [A] Step 2: Reductive ozonolysis of propene ([A]) splits the alkene at the C=C bond, creating ethanal ([B]) and methanal ([C]): CH_3-CH=CH_2 xrightarrowO_3, text then Zn/H_2O CH_3CHO\ [B] + HCHO\ [C] ### Step 1: Final Identification Hence, [A] = CH_3-CH=CH_2 [B] = CH_3CHO [C] = HCHO ### Pattern Recognition Whenever an alkyne undergoes partial hydrogenation with regular catalysts, count the carbons to trace the matching alkene framework. Cleaving a terminal alkene like propene always results in formaldehyde (HCHO) as one of the fragment products. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Hydrocarbons

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