One design feature commonly leveraged is the confinement and rigidity of the binding pocket. Similar to the dirhodium(II) catalysts, a more hindered CPA binding site is often connected to higher enantioselectivity. The dependence of CPA performance on 3,3' substitution was assessed by Goodman, showing that the positioning of steric bulk around the phosphoric acid controls reactivity by directing substrate orientation. From this model of reactivity it was hypothesized that SMART descriptors could aid in the comparison and selection of sterically hindered CPA structures.