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Organic reaction

physical science Maturity 9-11 Next article →

Organic reactions are chemical processes involving organic compounds. These reactions allow scientists to construct new organic molecules through specific changes. This ability is vital for modern life. We rely on organic reactions to produce many man-made chemicals. These include essential items like drugs, plastics, food additives, and fabrics.

Claisen rearrangement scheme
Claisen rearrangement scheme

Scientists classify these reactions in several ways. One method is by the basic reaction type. Common types include addition, elimination, and substitution reactions. Addition reactions involve adding parts to a molecule. Elimination reactions remove parts from a molecule. Substitution reactions replace one part of a molecule with another. Other types include pericyclic, rearrangement, photochemical, and redox reactions. Redox reactions involve the transfer of electrons between compounds.

Another way to group reactions is by their mechanism. This describes how the atoms actually move during the process. Polar reactions are the most common type. In these, electron pairs move from a source to a sink. The source is often a nucleophilic bond or a lone pair. The sink is an electrophilic center. This movement changes the charge of the participating atoms. Radical reactions involve species called radicals, which have unpaired electrons. These reactions move single electrons rather than pairs. Pericyclic reactions are unique because they involve a cyclic transition state. In these, electron pairs move around a cycle. They do not have a single source or a sink.

Chemists also use named reactions to identify specific processes. There are an estimated 1,000 named reactions in existence. These are often named after the person who discovered them. For example, the Claisen rearrangement was named in 1912. Some names are very long and difficult to say. The Corey–House–Posner–Whitesides reaction is a prime example. In such cases, scientists often use abbreviations like CBS reduction. Some names are simpler and hint at the process, such as the aldol reaction.

History shows how our understanding of these reactions has grown. The oldest known organic reactions are the combustion of fuels and saponification. Saponification is the process of making soap from fats. Modern organic chemistry is often said to have started with the Wöhler synthesis in 1828. Many major discoveries have earned the Nobel Prize in Chemistry. The Grignard reaction won in 1912. The Diels–Alder reaction was recognized in 1950. The Wittig reaction received the prize in 1979. Finally, olefin metathesis was honored in 2005.

Organic reactions are highly important in the pharmaceutical industry. A 2006 review analyzed how drugs are prepared. It found that 20% of chemical conversions involve alkylations on nitrogen and oxygen atoms. Another 20% involve the placement and removal of protective groups. About 11% of conversions involve the formation of new carbon–carbon bonds. Additionally, 10% involve functional group interconversions. These precise steps allow for the creation of complex medicine.

Claisen rearrangement scheme
Claisen rearrangement scheme

Specific factors influence how these reactions occur. Factors like conjugation, hyperconjugation, and aromaticity determine the stability of molecules. The presence of reactive intermediates also matters. These intermediates can include free radicals, carbocations, or carbanions. Reactions can also be categorized by the functional groups they involve. A functional group is a specific group of atoms within a molecule. For instance, the Fries rearrangement starts with an ester and produces an alcohol. Some reactions also change the carbon framework through ring expansion or ring contraction. This complexity connects organic chemistry to many other fields, including organometallic chemistry and metabolism.

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File:Claisen rearrangement scheme.svg
Claisen rearrangement scheme.svg
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