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SolutionsOxidation

1. Oxidations of 1-phenylcyclohexene

Predict the result of the following reactions:

1-Phenylcyclohexene with 1) MCPBA, CH₂Cl₂ and 2) H₂O, H⁺; with 1) KMnO₄ or OsO₄ and 2) H₂O, H⁺; with 1) O₃ and 2) Zn, AcOH, and with 1) O₃ and 2) H₂O₂, H⁺
MCPBA and hydrolysis give the racemic trans diol; KMnO₄ or OsO₄, the racemic cis diol; ozonolysis with Zn/AcOH gives 6-oxo-6-phenylhexanal and with H₂O₂/H⁺, 6-oxo-6-phenylhexanoic acid

Ozonolysis cleaves the double bond: since the ring is opened, a single compound bearing both carbonyls is obtained. The carbon that carried the phenyl gives a ketone and the other one an aldehyde (reductive work-up) or an acid (oxidative work-up).

2. Deduce the alkene

Ozonolysis with reductive work-up of an alkene C6H12 gives acetone and propanal. What is the alkene?

2-Methylpent-2-ene, (CH3)2C=CHCH2CH3: the two carbonyl carbons of acetone and propanal are joined by a double bond.

3. Baeyer test

What is observed when a dilute KMnO4 solution is added to cyclohexene and to cyclohexane? Why?

With cyclohexene the purple colour of permanganate disappears and a brown precipitate of MnO2 appears: the alkene is oxidized to the diol. With cyclohexane, which has no double bond, the purple colour remains.

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