Everything about Organic Reaction totally explained
Organic reactions are
chemical reactions involving
organic compounds. The basic
organic chemistry reaction types are
addition reactions,
elimination reactions,
substitution reactions,
pericyclic reactions,
rearrangement 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
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
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 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
There is no limit to the number of possible organic reactions and mechanisms. 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 isn't 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's intended to cover the basic reactions.
Elimination reactions include processes such as dehydration and are found to follow an E1, E2 or E1cB reaction mechanism
Substitution reactions are divided into:
nucleophilic aliphatic substitution with SN1, SN2 and SNi reaction mechanisms
nucleophilic aromatic substitution or NAS
nucleophilic acyl substitution
electrophilic substitution or ES
electrophilic aromatic substitution or EAS
radical substitution or RS
Organic redox reactions are redox reactions specific to organic compounds and are very common.
Rearrangement reactions are divided into:
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.
Organic reactions by functional groups
Organic reactions can be categorized based on the type of functional group involved in the reaction as a reactant and the functional group that's 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 on the right:
Other organic reaction classification
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.
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.
Further Information
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