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Organic reactions are chemical reactions involving . Strategic Applications of Named Reactions in Organic Synthesis Laszlo Kurti, Barbara Czako Academic Press (March 4, 2005) J. Clayden, N. Greeves & S. Warren "Organic Chemistry" (Oxford University Press, 2012)Robert T. Morrison, Robert N. Boyd, and Robert K. Boyd, Organic Chemistry, 6th edition, Benjamin Cummings, 1992 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.
Another approach to organic reactions is by type of organic reagent, many of them inorganic, required in a specific transformation. The major types are such as osmium tetroxide, such as lithium aluminium hydride, bases such as lithium diisopropylamide and such as sulfuric acid.
Finally, reactions are also classified by mechanistic class. Commonly these classes are (1) polar, (2) radical, and (3) pericyclic. Polar reactions are characterized by the movement of electron pairs from a well-defined source (a Nucleophile bond or lone pair) to a well-defined sink (an Electrophile center with a low-lying antibonding orbital). Participating atoms undergo changes in charge, both in the formal sense as well as in terms of the actual electron density. The vast majority of organic reactions fall under this category. Radical reactions are characterized by species with unpaired electrons (radicals) and the movement of single electrons. Radical reactions are further divided into chain and nonchain processes. Finally, pericyclic reactions involve the redistribution of chemical bonds along a cyclic transition state. Although electron pairs are formally involved, they move around in a cycle without a true source or sink. These reactions require the continuous overlap of participating orbitals and are governed by orbital symmetry considerations. Of course, some chemical processes may involve steps from two (or even all three) of these categories, so this classification scheme is not necessarily straightforward or clear in all cases. Beyond these classes, transition-metal mediated reactions are often considered to form a fourth category of reactions, although this category encompasses a broad range of elementary organometallic processes, many of which have little in common and very specific.
An organic compound may consist of many . 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 Zaitsev's rule.
Organic reactions are important in the production of Medication. In a 2006 review, 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, it was estimated that 20% of chemical conversions involved on nitrogen and oxygen atoms, another 20% involved placement and removal of , 11% involved formation of new carbon–carbon bond and 10% involved functional group interconversions.
| 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 specific to and are very common. | |
| Rearrangement reactions | 1,2-rearrangements | |
| pericyclic | ||
| metathesis |
In condensation reactions a small molecule, usually water, is split off when two 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.
An overview of functional groups with their preparation and reactivity is presented below:
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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, organosulfur chemistry, organophosphorus chemistry and organofluorine chemistry. With the introduction of carbon-metal bonds the field crosses over to organometallic chemistry.
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