The relative rates of rotation to ring closure were calculated by equations derived by Bartlett and co-workers with a correction by Orfanopoulos and co-workers . See the Supporting Information for details of the method and calculations. Using product distributions from trans,trans-diene 5 and the cis,cis-diene 6 Orfanopoulos and coworkers calculated k rot /k clos = ~18 . Repeating this calculation gave 18.4 in agreement. However, as shown in Figure , this analysis requires intermediates 13 and 16 to be interconverted by rotation about a single bond, which cannot occur as 13 is a trans-1-propenyl intermediate and 16 is a cis-1-propenyl intermediate.