or disrotatory electrocyclic reactions." In other words, a chemical reaction is torquoselective if the groups of atoms that hang from a ring of atoms are more likely to have rotated in a particular direction during the reaction (instead of being equally likely to rotate in both possible directions.) Torquoselectivity is different from the normal diastereoselectivity of pericyclic reactions. Instead it is more selectivity beyond the Woodward–Hoffmann rules. The name comes from the idea that the substituents in an electrocyclization appear to rotate during the reaction. The reaction produces a single product because only one direction of rotation was allowed (that is, the direction of rotation on the substituents was favored). The concept was originally developed by Kendall N. Houk.