The electronic activity along a reaction coordinate $$\xi$$ ξ can be rationalized in terms of the reaction electronic flux [REF, $$J(\xi )$$ J ( ξ ) ]. In this paper, its symmetry-adapted extension, $$J_{\rm s}(\xi )$$ J s ( ξ ) , is used to characterize the mechanism of two Diels–Alder reactions: butadiene plus ethylene to produce cyclohexene following a reaction path of $$C_{\rm s}$$ C s symmetry, and acetylene plus diacetylene to form o-benzyne in a $$C_{2v}$$ C 2 v reaction path. In the case of the former reaction, the electronic activity is captured in terms of the symmetry-adapted REF (SA-REF) according to irreducible representations $$A'$$ A ′ and $$A''$$ A ′ ′ . $$J_{A' }(\xi )$$ J A ′ ( ξ ) characterizes the electronic activity due to $$\pi$$ π electronic reordering, while $$J_{A''}(\xi )$$ J A ′ ′ ( ξ ) encompasses the formation of the new $$\sigma$$ σ bonds. The more complex o-benzyne formation displays four SA-REFs associated with each of the irreducible representation of the $$C_{2v}$$ C 2 v group. Results show that SA-REFs appear to be very useful for identifying electronic activity that displays an specific symmetry character. In the first reaction, the $$\pi$$ π electronic activity drives the formation of cyclohexene, whereas in the second reaction, the in-plane electronic activity drives the formation of o-benzyne.