Lack of intramolecular hydrogen bonding in glucopyranose: Vicinal hydroxyl groups exhibit negative cooperativity

Abstract

Stable conformers of glucopyranose in the gas-phase have their vicinal hydroxyl groups arranged in an apparent O A–H D⋯O A acceptor–donor–acceptor sequence. Notwithstanding this, there is no evidence of intramolecular hydrogen bonding based on the absence of (3, −1) bond critical points between the putative donors and acceptors. Moreover, these hydroxy groups show negative cooperativity (synergy) based on changes in O–H bond length, σ ∗ antibonding orbital occupancies, orbital overlap integrals, and IR blue-shifts compared to ethane-1,2-diol, rather than positive cooperativity as would be expected if intramolecular hydrogen bonding was present, suggesting that this interaction is on balance repulsive rather than attractive.