A condensation reaction is a reaction where two molecules join together and in doing so create a complex molecule and a much simpler molecule that is a byproduct of the reaction. The simple molecule eliminated can be water, ammonia, or an alcohol. The two combining molecules each contribute a single moiety (a part of portion of a molecule having a characteristic chemical property) to the eliminated molecule.

The formation of a peptide bond between two amino acids is an example of a condensation reaction, as is the manufacture of an ester (esterification).

Certain types of condensation reactions have their own name, for example the Claisen condensation. In this reaction, an ester joins with another ester, a ketone, or a nitrile. This must be carried out in the presence of sodium ethoxide that acts as a catalyst for the reaction. This type of reaction gives as its...