RCO2R

RCO2R is the general shorthand for an ester functional group in organic chemistry. It denotes a carbonyl carbon (C=O) adjacent to an OR' substituent, where R is an acyl group and R' is an alkyl or aryl group. The conventional representation is R–CO–O–R'. Esters can be acyclic or cyclic (the latter are called lactones). They are widely defined by their R and R' substituents and by their characteristic carbonyl infrared absorption around 1700 cm−1.

Most esters are formed by condensation of carboxylic acids and alcohols, known as Fischer esterification, typically catalyzed by an acid and driven by removal of water. Other routes include reaction of acid chlorides with alcohols or transesterification, in which the OR' group of an ester is exchanged for a different alkoxy group under acid or base catalysis. Esters also undergo hydrolysis to yield carboxylic acids or carboxylate salts and alcohols; this can occur under acidic or basic conditions. Reduction of esters with hydride donors affords primary alcohols, while other transformations can convert esters into a range of derivatives.

Esters have broad practical significance. They are common flavor and fragrance compounds and are also building blocks in synthesis. In industry, polyesters such as polyethylene terephthalate (PET) form the backbone of many plastics and fibers. Transesterification of triglycerides with short-chain alcohols produces biodiesel. Physically, esters vary in polarity and volatility with the alkyl groups; many small esters are volatile and possess characteristic pleasant odors, while larger ones are less volatile and more polar.