Xylopyranose Ring‐Opening by Single and Double Proton Transfers Under Pyrolysis Conditions

This study unveils a new transition state (TS) leading to the acyclic product via synchronous double proton transfer by automatedly exploring the potential energy surface of (Formula presented.) -D-xylopyranose under pyrolysis conditions. Quantum chemistry methods with multi-path canonical variational transition state theory show that the standard activation enthalpy of the new TS (44.9 kcal (Formula presented.)) is 1.5 kcal (Formula presented.) lower than that of the well-established channel; however, the latter's rate constant ((Formula presented.) – (Formula presented.) (Formula presented.)) is higher in the 673.15–873.15 K pyrolytic range by a factor of 5–8. This gap narrows to a factor of 2 within 320–400 K, signifying that the new TS can potentially impact the acyclic product production in this low-temperature regime. This is particularly relevant for (Formula presented.) -D-xylopyranose trimers, as the interior unit bears different substituents at the C1 and C3 positions.