Organic reaction

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The Claisen rearrangement

Organic reactions are chemical reactions involving organic compounds.[1] The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthesis, organic reactions are used in the construction of new organic molecules. The production of many man-made chemicals such as drugs, plastics, food additives, fabrics depend on organic reactions.

The oldest organic reactions are combustion of organic fuels and saponification of fats to make soap. Modern organic chemistry starts with the Wöhler synthesis in 1828. In the history of the Nobel Prize in Chemistry awards have been given for the invention of specific organic reactions such as the Grignard reaction in 1912, the Diels-Alder reaction in 1950, the Wittig reaction in 1979 and olefin metathesis in 2005.

Classifications[edit]

Organic chemistry has a strong tradition of naming a specific reaction to its inventor or inventors and a long list of so-called named reactions exists, conservatively estimated at 1000. A very old named reaction is the Claisen rearrangement (1912) and a recent named reaction is the Bingel reaction (1993). When the named reaction is difficult to pronounce or very long as in the Corey-House-Posner-Whitesides reaction it helps to use the abbreviation as in the CBS reduction. The number of reactions hinting at the actual process taking place is much smaller, for example the ene reaction or aldol reaction.

Another approach to organic reactions is by type of organic reagent, many of them inorganic, required in a specific transformation. The major types are oxidizing agents such as osmium tetroxide, reducing agents such as Lithium aluminium hydride, bases such as lithium diisopropylamide and acids such as sulfuric acid.

Fundamentals[edit]

Factors governing organic reactions are essentially the same as that of any chemical reaction. Factors specific to organic reactions are those that determine the stability of reactants and products such as conjugation, hyperconjugation and aromaticity and the presence and stability of reactive intermediates such as free radicals, carbocations and carbanions.

An organic compound may consist of many isomers. Selectivity in terms of regioselectivity, diastereoselectivity and enantioselectivity is therefore an important criterion for many organic reactions. The stereochemistry of pericyclic reactions is governed by the Woodward–Hoffmann rules and that of many elimination reactions by the Zaitsev's rule.

Organic reactions are important in the production of pharmaceuticals. In a 2006 review[2] it was estimated that 20% of chemical conversions involved alkylations on nitrogen and oxygen atoms, another 20% involved placement and removal of protective groups, 11% involved formation of new carbon-carbon bond and 10% involved functional group interconversions.

Organic reactions by mechanism[edit]

There is no limit to the number of possible organic reactions and mechanisms.[3] However, certain general patterns are observed that can be used to describe many common or useful reactions. Each reaction has a stepwise reaction mechanism that explains how it happens, although this detailed description of steps is not always clear from a list of reactants alone. Organic reactions can be organized into several basic types. Some reactions fit into more than one category. For example, some substitution reactions follow an addition-elimination pathway. This overview isn't intended to include every single organic reaction. Rather, it is intended to cover the basic reactions.

Reaction type Subtype Comment
Addition reactions electrophilic addition include such reactions as halogenation, hydrohalogenation and hydration.
nucleophilic addition
radical addition
Elimination reaction include processes such as dehydration and are found to follow an E1, E2 or E1cB reaction mechanism
Substitution reactions nucleophilic aliphatic substitution with SN1, SN2 and SNi reaction mechanisms
nucleophilic aromatic substitution
nucleophilic acyl substitution
electrophilic substitution
electrophilic aromatic substitution
radical substitution
Organic redox reactions are redox reactions specific to organic compounds and are very common.
Rearrangement reactions 1,2-rearrangements
pericyclic reactions
metathesis

In condensation reactions a small molecule, usually water, is split off when two reactants combine in a chemical reaction. The opposite reaction, when water is consumed in a reaction, is called hydrolysis. Many Polymerization reactions are derived from organic reactions. They are divided into addition polymerizations and step-growth polymerizations.

In general the stepwise progression of reaction mechanisms can be represented using arrow pushing techniques in which curved arrows are used to track the movement of electrons as starting materials transition to intermediates and products.

Organic reactions by functional groups[edit]

Organic reactions can be categorized based on the type of functional group involved in the reaction as a reactant and the functional group that is formed as a result of this reaction. For example in the Fries rearrangement the reactant is an ester and the reaction product an alcohol.

An overview of functional groups with their preparation and reactivity is presented below:

Functional group Preparation Reactions
Acid anhydride preparation reactions
Acyl halides preparation reactions
Acyloins preparation reactions
Alcohols preparation reactions
Aldehydes preparation reactions
Alkanes preparation reactions
Alkenes preparation reactions
Alkyl halides preparation reactions
Alkyl nitrites preparation reactions
Alkynes preparation reactions
Amides preparation reactions
Amine oxide preparation reactions
Amines preparation reactions
Arene compounds preparation reactions
Azides preparation reactions
Aziridines preparation reactions
Carboxylic acids preparation reactions
Cyclopropanes preparation reactions
Diazo compounds preparation reactions
Diols preparation reactions
Esters preparation reactions
Ethers preparation reactions
Epoxide preparation reactions
Haloketones preparation reactions
Imines preparation reactions
Isocyanates preparation reactions
Ketones preparation reactions
Lactams preparation reactions
Nitriles preparation reactions
Nitro compounds preparation reactions
Phenols preparation reactions
Thiols preparation reactions

Other organic reaction classification[edit]

In heterocyclic chemistry, organic reactions are classified by the type of heterocycle formed with respect to ring-size and type of heteroatom. See for instance the chemistry of indoles. Reactions are also categorized by the change in the carbon framework. Examples are ring expansion and ring contraction, homologation reactions, polymerization reactions, insertion reactions, ring-opening reactions and ring-closing reactions.

Organic reactions can also be classified by the type of bond to carbon with respect to the element involved. More reactions are found in organosilicon chemistry, organosulfur chemistry, organophosphorus chemistry and organofluorine chemistry. With the introduction of carbon-metal bonds the field crosses over to organometallic chemistry.

CH He
CLi CBe CB CC CN CO CF Ne
CNa CMg CAl CSi CP CS CCl CAr
CK CCa CSc CTi CV CCr CMn CFe CCo CNi CCu CZn CGa CGe CAs CSe CBr CKr
CRb CSr CY CZr CNb CMo CTc CRu CRh CPd CAg CCd CIn CSn CSb CTe CI CXe
CCs CBa CHf CTa CW CRe COs CIr CPt CAu CHg CTl CPb CBi CPo CAt Rn
Fr CRa Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo
CLa CCe CPr CNd CPm CSm CEu CGd CTb CDy CHo CEr CTm CYb CLu
Ac CTh CPa CU CNp CPu CAm CCm CBk CCf CEs Fm Md No Lr
Chemical bonds to carbon
Core organic chemistry Many uses in chemistry
Academic research, but no widespread use Bond unknown

See also[edit]

References[edit]

  1. ^ Strategic Applications of Named Reactions in Organic Synthesis Laszlo Kurti, Barbara Czako Academic Press (March 4, 2005) ISBN 0-12-429785-4
  2. ^ Analysis of the reactions used for the preparation of drug candidate molecules John S. Carey, David Laffan, Colin Thomson and Mike T. Williams Org. Biomol. Chem., 2006, 4, 2337–2347, doi:10.1039/b602413k
  3. ^ Is This Reaction a Substitution, Oxidation-Reduction, or Transfer? / N.S.Imyanitov. J. Chem. Educ. 1993, 70(1), 14 – 16.

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