Reduction in the cavity is more pronounced in water with a change in cavity volume from RS to post-TS of -60 Å³ compared to methanol (-40 Å³). The decrease in cavity volume is entropically unfavourable as it implies the formation of a more ordered solvent structure. However, at the same time, it is enthalpically favourable due to the formation of HBs among solvent-solvent (rather than solvent-solute) molecules, resulting in a decrease in ∆G ‡ . The importance of HB formation is supported by analysing the average number of HBs per solvent molecule at increasing distances from the solute. The distance was measured between the oxygen atom of the solvent and the centre of mass (CoM) of the RS, intermediate, and PS. Since the reaction passes the TS very quickly, the intermediate was chosen for analysis instead.