Side reaction
A side reaction is a chemical reaction that occurs at the same time as the actual main reaction, but to a lesser extent. It leads to the formation of by-product, so that the yield of main product is reduced: {A} + B ->[{k_1}] P1 {A} + C ->[{k_2}] P2 P1 is the main product if k1> k2. The by-product P2 is generally undesirable and must be separated from the actual main product (usually in a costly process). In organic synthesis B and C from the above equations usually represent different compounds. However, they could also just be different positions in the same molecule. A side reaction is also referred to as competing reaction when different compounds (B, C) compete for another reactant (A). If the side reaction occurs about as often as the main reaction, it is spoken of parallel reactions (especially in the kinetics, see below). Also there may be more complicated relationships: Compound A could reversibly but quickly react to substance B (with speed k1) or irreversible but slow (k1> k−1 >> k2) to substance C: B <=> A ->[{k_2}] C Assuming that the reaction to substance C is irreversible, as it is thermodynamically very stable. In this