As illustrated in the partial space-filling models of the ring-opening transition states for different azetidine and oxetane derivatives, 1a induces high enantioselectivity even as the size of the activated fragments (OH, OTMS, NR2, Vfrag. = 34-400Å 3 ) and the percent buried volume of the activated heteroatom (Vburr. = 44-85%) varies substantially (Figure ). In contrast, the electrostatic topology of the transition states is largely conserved across the series (Figure ). The reactions producing 3a and 4b -those computed to proceed through the most and least voluminous transition states, respectively -were performed with six different catalysts (1a-1g). A comparison of the enantioselectivity in the two reactions (plotted as ΔΔG ‡ ) revealed a linear free correlation (R 2 = 0.94) (Figure 3E, top). Similarly good linear free-energy correlations were obtained in comparisons of each of the four model reactions (Figure 3E, bottom). These results are most consistent with a mechanism of enantioinduction ) and enantioselectivity (ΔΔG ‡ , calculated as -RTln(enantiomer ratio)) for formation of 3aa with catalysts 1a-g. C. partial space-filling models of transition states that lead to products 3a, 3aa, 4a, and 4b with their activated fragments represented as electron density iso-surfaces. All calculations performed with pcm(Et2O)-B3LYP-D3BJ/6-311+G(d,p)//pcm(Et2O)-B3LYP-/6-31G (d). D. Electron density isosurfaces colored by electrostatic potential for transition states that lead to products 3a, 3aa, 4a, and 4b (with catalyst 1a omitted for clarity). E. Linear free energy correlation of enantioselectivity (expressed as ΔΔG ‡ ) for formation of 3a and 3aa with catalysts 1a-g (top) and correlations for reactions yielding 3a, 3aa, 4a, and 4b with catalysts 1a-g (bottom).