Electrocyclic reactions are a type of organic reaction where a conjugated system undergoes a ring closure or ring opening in response to heat or light. These reactions typically involve the formation or breaking of sigma bonds while maintaining a cyclic structure, often resulting in the conversion of a linear molecule into a cyclic one or vice versa. The mechanism of electrocyclic reactions is governed by the Woodward-Hoffmann rules, which predict the stereochemistry and feasibility of the reaction based on the number of π electrons involved. These rules help chemists understand how the reaction proceeds under different conditions, such as thermal or photochemical activation.