Furan solvation challenge

We wanted to kick off a medium- to long-term benchmarking challenge, starting with the methanol solvation preference of 2,5-dimethylfuran, which was recently shown to be subtle, but experimentally tractable (doi:10.1039/c6cp05413g). Furan offers a planar scaffold with many potential modification options via alkyl and other substitution. Methanol can also be easily modified by alkylation. The methanol-furan contact pair is small enough to leave some hope for future anharmonic treatments of zero point energy, but large enough to render this a major challenge for relative energy predictions on the sub-kJ/mol scale. The results of the challenge provided helpful clues in the design of future test systems.

The systems considered in this challenge were the dimers of furan/methanol, 2-methylfuran/methanol and 2,5-dimethylfuran/methanol. The complex of methanol with 2,5-dimethylfuran provided a starting point. Our experiments indicated a slight preference for oxygen coordination (doi:10.1039/c6cp05413g). Rough DFT calculations (see the supplementary information) indicated a slight trend towards carbon (or π) coordination of the methanol OH group with stepwise de-methylation of the furan scaffold.

The challenge consisted on the (blind) theoretical calculation of the trend. The goal was to present the best possible predictions for the energy difference (at 0K) between the two possible modes of binding. The first phase has been completed and the results have been published in J. Chem. Phys. 148, 014301 (2018). A second evaluation is currently taking place, with improved error bars to the experimental estimates and structural information on the furan-methanol dimer.