Kinetic measurements for alkene epoxidation reactions with H 2 O 2 provide an ideal method to examine the catalytic consequences of the structure and dynamics of intraporous H 2 O, because these reactions exhibit rates that depend strongly on the density of (SiOH) x and size of the confining pore. 18,39,40 Figure shows rates of 1-alkene epoxidation are 10 -400-fold greater in zeolites that contain significant densities of (SiOH) x (i.e., are hydrophilic) than the analogous structures with far fewer (SiOH) x . The rates of 1-alkene epoxidation are ~10-fold greater in Ti-FAU-OH than Ti-FAU-F (Fig. ) and depend weakly on the chain length of the 1-alkene. Turnover rates for 1-hexene epoxidation are 60-times higher within Ti-BEA-OH in comparison to Ti-BEA-F (Fig. ), and the difference between rates in hydrophilic and hydrophobic variants increases with 1-alkene chain length to a difference of 150-fold for 1-decene. Finally, the ratio of epoxidation rates within Ti-MFI-OH to those in Ti-MFI-F increase from a ratio of 100x to 400x as the 1-alkene is changed from 1-hexene to 1-decene (Fig. ). These differences in turnover rates among Ti-zeolites and 1-alkenes do not reflect differences in the mechanism for epoxidation or differences in the electronic properties of the active sites. Rather, vast range of epoxidation rates among Ti-zeolite with distinct topologies and (SiOH) x densities reflects differences between the structures of solvent molecules that solvate reactive intermediates and transition states at Ti active sites and that recognize the shape, size, and polarity of the surrounding voids. Silanol functions that neighbor Ti active sites nucleate structures of H 2 O that reorganize in response to the individual elementary steps during epoxidation catalysis. The extent by which solvent molecules must restructure depends on the dimensions of the reactive intermediates, the initial structure of the solvent molecules (that depend on zeolite topology and polarity), and the type and strength of specific interactions between the solvent and reactive species. Consequently, the size of the 1-alkene correlates to the average number of hydrogen bonds and solvent molecules disturbed to accommodate the surface intermediates and transition states for epoxidation. Under reaction conditions where the concentration of H 2 O 2 exceeds that of the 1-alkene, pools of Ti-OOH and Ti-(η 2 -O 2 ) intermediates comprise the most abundant reactive intermediate (MARI; collectively denoted as Ti-OOH) which leads to the following rate expression for alkene epoxidation