6.03 | Conservation of Symmetry in Electrocyclic Reactions

Sunday August 18th, 2024 | In this last lecture of Advanced Organic Chemistry, we discussed the conservation of symmetry in electrocyclic reactions. We stated in class the 4n+2 (electron) reaction will undergo ring-closing or ring-opening in a disrotatory fashion, while 4n (electron) reaction will undergo the ring-opening or ring-closing reaction in a conrotatory reaction. These rules are evident by analyzing the the HOMO of the conjugated π-system, or even better, by drawing orbital correlation diagrams. By doing so, we indeed visualized that the ground-state electronic configuration of cyclobutadiene leads to the ground-state configuration of cyclobutene, when the electrocyclic ring-closing reaction is conrotatory (4n). However, we also observed that if we would irradiate the reaction, the excite state of the reaction would lead to an excited-state of the product, when the ring-opening occurs in a disrotatory fashion. As such we established that for 4n (electron) reactions in a conrotatory fashion are thermally allowed, while 4n (electron) reaction in a disrotatory fashion are photochemically allowed.

The link to the video can be found below