Finally, there’s a second type of reaction that involves two π-bonds being transformed into two σ-bonds. The difference here is that two bonds are formed (or broken) at a single atom, while in cycloaddition reactions, only one bond is made at each reactive atom. An example involving SO₂ is shown below (surprisingly this reaction isn’t named after anyone!). In this reaction both σ-bonds are made (or broken) at the sulfur atom. Compare this with the Diels-Alder reaction mentioned above, where the two new σ-bonds are connected to the two different ends of the dieneophile.