kcal/mol. The difference in calculated free energy of the combined molecule compared to the isolated components is rather larger at +2.7 kcal/mol, but it is suggestive that such a composite model containing a modest proportion of discrete hydrogen-bonded chloroform solvation could explain the reduced experimental KIE. Another outlier apparent in the original report is the temperature variation of the KIE in dichloromethane as solvent. The original Arrhenius plot (Figure of article 9 ), recalculated below as an Eyring plot (Figure ), can be re-interpreted as showing linear behaviour for the experimental values between 250 -210K and an outlying value at 195K. In contrast, all the various computed models discussed (Tables ) above show linear behaviour across the entire temperature range. Ostensibly, the experimental value at 195K could indicate a relatively abrupt increase in tunnelling to explain the unexpectedly large value of the KIE at this temperature; a linear extrapolation would suggest the observed value should only be reached at ~172K. Only further experimental analysis exploring the KIE in the region surrounding 195-210K would resolve whether this is a fascinating real effect or an experimental artefact. More sophisticated tunnelling models involving could also help resolve this aspect. We may reasonably conclude from the clustering of the calculated isotope effects around or above the experiment points (Figure )