A solution of 5-methylcyclopenta-1,3-diene rearranges at roomtemperature to a mixture containing 1-methyl-, 2-methyl-, and 5-methylcyclopenta-1,3-diene. (a) Show how both isomeric products areformed from the starting material by a sigmatropic rearrangementinvolving a C–H bond. (b) Explain why 2-methylcyclopenta-1,3-diene isnot formed directly from 5-methylcyclopenta-1,3-diene by a [1,3]rearrangement.

A solution of 5-methylcyclopenta-1,3-diene rearranges at roomtemperature to a mixture containing 1-methyl-, 2-methyl-, and 5-methylcyclopenta-1,3-diene. (a) Show how both isomeric products areformed from the starting material by a sigmatropic rearrangementinvolving a C–H bond. (b) Explain why 2-methylcyclopenta-1,3-diene isnot formed directly from 5-methylcyclopenta-1,3-diene by a [1,3]rearrangement.

Organic Chemistry

9th Edition

ISBN:9781305080485

Author:John E. McMurry

Publisher:John E. McMurry

Chapter14: Conjugated Compounds And Ultraviolet Spectroscopy

Section14.SE: Something Extra

Problem 50AP: -Ocimene is a pleasant-smelling hydrocarbon found in the leaves of certain herbs. It has the...

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The reaction of butan-2-ol with concentrated aqueous HBr goes with partial racemization, giving more inversion thanretention of configuration. Propose a mechanism that accounts for racemization with excess inversion.(b) Under the same conditions, an optically active sample of trans-2-bromocyclopentanol reacts with concentrated aqueous HBr to give an optically inactive product, (racemic) trans-1,2-dibromocyclopentane. Proposea mechanism to show how this reaction goes with apparently complete retention of configuration, yet withracemization. (Hint: Draw out the mechanism of the reaction of cyclopentene with Br2 in water to give thestarting material, trans-2- bromocyclopentanol. Consider how parts of this mechanism might be involved in thereaction with HBr.)
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-Ocimene is a pleasant-smelling hydrocarbon found in the leaves of certain herbs. It has the molecular formula C10H16 and a UV absorption maximum at 232 nm. On hydrogenation with a palladium catalyst, 2,6-dimethyloctane is obtained. Ozonolysis of -ocimene, followed by treatment with zinc and acetic acid, produces the following four fragments: (a) How many double bonds does -ocimene have? (b) Is -ocimene conjugated or nonconjugated? (c) Propose a structure for -ocimene. (d) Write the reactions, showing starting material and products.