Organic reduction

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Organic reductions or organic oxidations or organic redox reactions are redox reactions that take place with organic compounds. In organic chemistry oxidations and reductions are different from ordinary redox reactions because many reactions carry the name but do not actually involve electron transfer in the electrochemical sense of the word.

Following the rules for determining the oxidation number for an individual carbon atom leads to

oxidation number -4 for alkanes,
oxidation number -2 for alkenes, alcohols, alkyl halides, amines,
oxidation number 0 for alkynes, ketones, aldehydes, geminal diols,
oxidation number +2 for carboxylic acids, amides, chloroform and
oxidation number +4 for carbon dioxide, tetrachloromethane.

Methane is oxidized to carbon dioxide because the oxidation number changes from -4 to +4. Classical reductions include alkene reduction to alkanes and classical oxidations include oxidation of alcohols to aldehydes with manganese dioxide. In oxidations electrons are removed and the electron density of a molecule is reduced. In reductions electron density increases when electrons are added to the molecule. This terminology is always centered around the organic compound. So a ketone is always reduced by Lithium aluminium hydride but it is bad form to have lithium aliminium hydride oxidized by a ketone. Many oxidations involve removal of protons from the organic molecule and the reverse reduction adds protons to an organic molecule.

Many reactions classified as reductions also appear in other classes. For instance conversion of the ketone to an alcohol by Lithium aluminium hydride can be considered a reduction but the hydride is also a good nucleophile in nucleophilic substitution. Many redox reactions in organic chemistry have coupling reaction reaction mechanism involving free radical intermediates. True organic redox chemistry can be found in electrochemical organic synthesis. Examples of organic reactions that can take place in a electrochemical cell are the Kolbe electrolysis [link]

Organic reductions

Several reaction mechanisms exist for organic reductions:

Direct electron transfer in one-electron reduction with the Birch reduction as example
Hydride transfer in reductions with for example Lithium aluminium hydride
Hydrogen reductions with a catalyst such as the Lindlar catalyst or the Adkins catalyst or in specific reductions such as the Rosenmund reduction.
Disproportionation reaction such as the Cannizzaro reaction

Reductions that do not fit in any reduction reaction mechanism and in which just the change in oxidation state is reflected include the Wolff-Kishner reaction.

Organic oxidations

Several reaction mechanisms exist for organic oxidations:

Single electron transfer
Oxidations through ester intermediates with chromic acid or manganese dioxide
Hydrogen atom transfer as in Free radical halogenation
Oxidation with oxygen (combustion)
Oxidation involving ozone in ozonolysis and peroxides
Oxidations involving a elimination reaction mechanism such as the Swern oxidation, the Kornblum oxidation and with reagents such as IBX acid and Dess-Martin periodinane.
oxidation by nitroso radicals Fremy's salt or TEMPO

Topics in Organic Reactions
Addition reaction \| Elimination reaction \| Polymerization \| \| Rearrangement reaction \| Redox reaction \| Regioselectivity \| Stereoselectivity \| Substitution reaction
List of organic reactions

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