Organic reactions. Synthetic organic chemistry

 

     Organic reactions are chemical reactions involving organic compounds. While pure hydrocarbons undergo certain limited classes of reactions, many more reactions which organic compounds undergo are largely determined by functional groups. The general theory of these reactions involves careful analysis of such properties as the electron affinity of key atoms, bond strengths and steric hindrance.     These issues can determine the relative stability of short-lived reactive intermediates, which usually directly determine the path of the reaction. An example of a common reaction is a substitution reaction written as: Nu? + C-X > C-Nu + X?  where X is some functional group and Nu is a nucleophile.

     There are many important aspects of a specific reaction. Whether it will occur spontaneously or not is determined by the Gibbs free energy change of the reaction. The heat that is either produced or needed by the reaction is found from the total enthalpy change. Other concerns include whether side reactions occur from the same reaction conditions. Any side reactions which occur typically produce undesired compounds which may be anywhere from very easy or very difficult to separate from the desired compound.

Synthetic organic chemistry

     Synthetic organic chemistry is an applied science as it borders engineering, the "design, analysis, and/or construction of works for practical purposes". Organic synthesis of a novel compound is a problem solving task, where a synthesis is designed for a target molecule by selecting optimal reactions from optimal starting materials. Complex compounds can have tens of reaction steps that sequentially build the desired molecule. The synthesis proceeds by utilizing the reactivity of the functional groups in the molecule. For example, a carbonyl compound can be used as a nucleophile by converting it into an enolate, or as an electrophile; the combination of the two is called the aldol reaction. Designing practically useful syntheses always requires conducting the actual synthesis in the laboratory. The scientific practice of creating novel synthetic routes for complex molecules is called total synthesis.

     There are several strategies to design a synthesis. The modern method of retrosynthesis, developed by E.J. Corey, starts with the target molecule and splices it to pieces according to known reactions. The pieces, or the proposed precursors, receive the same treatment, until available and ideally inexpensive starting materials are reached. Then, the retrosynthesis is written in the opposite direction to give the synthesis. A "synthetic tree" can be constructed, because each compound and also each precursor has multiple syntheses.