Chemoselectivity
Encyclopedia
Chemical reactions are defined usually in small contexts (only up to a small number of neighbouring atoms), such generalizations are a matter of utility. The preferential outcome of one instance of a generalized reaction over a set of other plausible reactions, is defined as chemoselectivity.
In another definition, chemoselectivity refers to the selective reactivity of one functional group
in the presence of others; often this process in convoluted and protecting groups are used to ensure that this outcome can be attained. Practicing chemists typically try to predict whether or not an instance of a particular generalized reaction will yield product based on the molecular connectivity alone. Such predictions based on connectivity are generally considered plausible, but the physical outcome of the actual reaction is ultimately dependent on a number of factors that are practically impossible to predict to any useful accuracy (solvent, atomic orbitals, etc.).
As such, chemoselectivity can be difficult to predict, but observing selective outcomes in cases where many reactions are plausible, is common. Examples include the selective organic reduction
of 4-nitro-2-chlorobenzonitrile to the corresponding aniline, 4-amino-2-chlorobenzonitrile and the greater relative chemoselectivity of sodium borohydride
reduction
vs. lithium aluminium hydride
reduction
. In another example, the compound 4-methoxyacetophenone is oxidized by bleach
at the ketone group at high pH (forming the carboxylic acid
) and oxidized by EAS
(to the aryl chloride) at low pH
In another definition, chemoselectivity refers to the selective reactivity of one functional group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...
in the presence of others; often this process in convoluted and protecting groups are used to ensure that this outcome can be attained. Practicing chemists typically try to predict whether or not an instance of a particular generalized reaction will yield product based on the molecular connectivity alone. Such predictions based on connectivity are generally considered plausible, but the physical outcome of the actual reaction is ultimately dependent on a number of factors that are practically impossible to predict to any useful accuracy (solvent, atomic orbitals, etc.).
As such, chemoselectivity can be difficult to predict, but observing selective outcomes in cases where many reactions are plausible, is common. Examples include the selective organic reduction
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
of 4-nitro-2-chlorobenzonitrile to the corresponding aniline, 4-amino-2-chlorobenzonitrile and the greater relative chemoselectivity of sodium borohydride
Sodium borohydride
Sodium borohydride, also known as sodium tetrahydridoborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a versatile reducing agent that finds wide application in chemistry, both in the laboratory and on a technical scale. Large amounts are...
reduction
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
vs. lithium aluminium hydride
Lithium aluminium hydride
Lithium aluminium hydride, commonly abbreviated to LAH or known as LithAl, is an inorganic compound with the chemical formula LiAlH4. It was discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters,...
reduction
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
. In another example, the compound 4-methoxyacetophenone is oxidized by bleach
Bleach
Bleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...
at the ketone group at high pH (forming the carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
) and oxidized by EAS
Electrophilic aromatic substitution
Electrophilic aromatic substitution EAS is an organic reaction in which an atom, usually hydrogen, appended to an aromatic system is replaced by an electrophile...
(to the aryl chloride) at low pH