Condensation Reaction

∞ generated and posted on 2016.12.21 ∞

Combining of two compounds into a single compound that occurs in association with the loss of a small molecule between them.

In dehydration synthesis the small molecule that is lost is water and this is the most biologically relevant of condensation reactions. See also synthesis reaction.

Figure legend: Shown is the opposing chemical reaction going from top to bottom (dehydration synthesis, a.k.a., condensation reaction). Hydrolysis instead is shown going from bottom to top. Note the insertion of the water molecule into the central bond between subunits, also known as moieties at this point, such as in amino acid moiety.

Strictly you should view condensation reactions as reducing, that is, "condensing" the number of components over the course of a chemical reaction, though with the caveat that the number of chemical players does not actually decline in number, i.e., A-X + Y-B → A-B + X-Y strictly stays the same number-wise. Note that X-Y here is the small molecule that has been lost and that in a dehydration synthesis reaction -X could be equivalent to -OH and -Y the equivalent of -H.

Alternatively, and not necessarily how a chemist would strive to memorize this, you could consider the condensation of two reactants into a single compound as resulting in water "condensing" out of the two reactants. This does not strictly result in condensation as in the "sweating" of a cold drink on a humid day. Nonetheless, such a condensation reaction would serve to increase water concentrations which, if in vapor form and sufficiently abundant, could lead to such condensation. Just keep in mind, however, that this description should be used as mnemonic rather than as a literal description of "condensation" as it occurs during all condensation reactions.