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1. Reactions of 2-methyl-1-phenylcyclohexene

Starting from 2-methyl-1-phenylcyclohexene, predict the outcome of the reactions in the table:

The table asks for the products of twelve reactions of 2-methyl-1-phenylcyclohexene: catalytic hydrogenation; addition of Br₂; Br₂ with excess NaCl; I₂ in water; Cl₂ in ethanol; HBr; HBr with H₂O₂; H₂O in acid; oxymercuration-demercuration; hydroboration-oxidation; ozonolysis with reductive and with oxidative work-up; MCPBA then hydrolysis; MnO₄⁻ then hydrolysis; OsO₄ then hydrolysis
Products: cis-1-methyl-2-phenylcyclohexane (racemic); anti dibromide; anti bromochlorides with Cl on the benzylic carbon (major); anti iodohydrin and chloroether with OH or OEt on the benzylic carbon; bromide on the benzylic carbon with HBr and on the methyl-bearing carbon with HBr and peroxides; tertiary benzylic alcohol with H₂O/H⁺ and with mercury; anti-Markovnikov alcohol with OH and H cis by hydroboration; the same open-chain diketone, 1-phenylheptane-1,6-dione, by ozonolysis with either work-up; trans diol with MCPBA and hydrolysis, and cis diol with permanganate or osmium tetroxide

There are three keys: the carbocation (or the quasi-carbocation of the halonium or mercurinium ion) forms on the benzylic, tertiary carbon, which stabilizes it best; additions through cyclic ions are anti; hydrogenation, hydroboration and dihydroxylation with MnO4− or OsO4 are syn additions.

2. Which reagent would you use?

Give the reagent or sequence of reagents to convert 1-methylcyclohexene into:

  1. Methylcyclohexane
  2. 1-Methylcyclohexanol
  3. trans-2-Methylcyclohexanol
  4. cis-1-Methylcyclohexane-1,2-diol
  5. 6-Oxoheptanal
  1. H2, Pd/C.
  2. H2O/H+ or, better, oxymercuration-demercuration ((AcO)2Hg, H2O; NaBH4).
  3. Hydroboration-oxidation: BH3 then H2O2, HO−.
  4. OsO4 (or cold dilute KMnO4) then hydrolysis.
  5. Ozonolysis with reductive work-up: O3 then (CH3)2S or Zn/AcOH.

3. Degrees of unsaturation

A hydrocarbon C6H10 takes up 1 mol of H2 on catalytic hydrogenation. How many rings does it have? Propose a structure.

C6H10 has (2·6 + 2 − 10)/2 = 2 degrees of unsaturation. Since there is only one double bond (1 mol of H2), the other degree is a ring: for example, cyclohexene.

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