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Chapter 20 More About Oxidation–Reduction Reactions. Organic Chemistry 6 th Edition Paula Yurkanis Bruice. Oxidation is always coupled with reduction. Loss of electrons is oxidation. Gain of electrons is reduction. The oxidation state of a carbon atom equals the total
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Chapter 20 More About Oxidation–Reduction Reactions Organic Chemistry 6th Edition Paula Yurkanis Bruice
Oxidation is always coupled with reduction. • Loss of electrons is oxidation. • Gain of electrons is reduction. • The oxidation state of a carbon atom equals the total • number of its C—O, C—N, and C—X bonds.
Reduction at carbon increases the number of C—H bonds or • decreases the number of C—O, C—N, or C—X bonds. • Oxidation at carbon decreases the number of C—H bonds or • increases the number of C—O, C—N, or C—X bonds.
Hydrogen, sodium borohydride, and hydrazine are the reducing agents:
H2, Pd on charcoal Na or Li metal in liq NH3 NaBH4 or LiAlH4 H2 as a Reducing Agent
Reduction by Catalytic Hydrogenation Addition of two hydrogen atoms:
Only the alkene substituted to benzene is reduced: Reduction of carbon–nitrogen double and triple bonds:
Dissolving-Metal Reduction Addition of an electron, a proton, an electron, and a proton:
Reduction by Addition of a Hydride Ion and a Proton
Aldehydes, ketones, and acyl halides can be reduced to alcohols by sodium borohydrides:
LiAlH4 is a stronger reducing agent than NaBH4 LiAlH4 is used to reduce compounds that are unreactive toward NaBH4
DIBALH allows the addition of one equivalent of hydride to an ester: Replacing some of the hydrogens of LiAlH4 with –OR groups decreases the reactivity of the metal hydride:
NaBH4 can be used to selectively reduce an aldehyde or a keto group in a compound: Alkenes and alkynes do not possess a partial positive charge:
Sodium borohydride can be used as a chemoselective reducing agent:
Mechanism of Alcohol Oxidation by the Swern Oxidation
Both aldehydes and ketones can be oxidized by peroxyacid: the Baeyer–Villiger oxidation
Mechanism of the Baeyer–Villiger Oxidation
Controlling Stereochemistry in Synthesis An enantioselective reaction forms more of one enantiomer than of another:
Mechanism for cis-Glycol Formation Higher yields of the diol are obtained with osmium tetroxide than with permaganate
The alkene and ozone undergo a concerted six-electron cycloaddition Mechanism of ozonide formation: The molozonide is unstable because it has two O—O bonds, but the ozonide is stable
The benzene ring is not oxidized under mild ozonolysis conditions:
Oxidative Cleavage of Alkynes The same reagents that oxidize alkenes also oxidize alkynes:
Designing a Synthesis by Functional Group Interconversion Conversion of an aldehyde to other functional groups:
Conversion of a Ketone into an Ester or an Alcohol