Intramolecular OH⋅⋅⋅fluorine hydrogen bonding in saturated, acyclic fluorohydrins : the γ-fluoropropanol motif

Fluorination is commonly exercised in compound property optimization. However, the influence of fluorination on hydrogen-bond (HB) properties of adjacent functional groups, as well as the HB-accepting capacity of fluorine itself, is still not completely understood. Although the formation of OH center dot center dot center dot F intramolecular HBs (IMHBs) has been established for conformationally restricted fluorohydrins, such interaction in flexible compounds remained questionable. Herein is demonstrated for the first time-and in contrast to earlier reports-the occurrence of OH center dot center dot center dot F IMHBs in acyclic saturated g-fluorohydrins, even for the parent 3-fluoropropan-1-ol. The relative stereochemistry is shown to have a crucial influence on the corresponding (h1)J(OH center dot center dot center dot F) values, as illustrated by syn- and anti-4-fluoropentan-2-ol (6.6 and 1.9 Hz). The magnitude of OH center dot center dot center dot F IMHBs and their strong dependence on the overall molecular conformational profile, fluorination motif, and alkyl substitution level, is rationalized by quantum chemical calculations. For a given alkyl chain, the "rule of shielding" applies to OH center dot center dot center dot F IMHB energies. Surprisingly, the predicted OH center dot center dot center dot F IMHB energies are only moderately weaker than these of the corresponding OH center dot center dot center dot OMe. These results provide new insights of the impact of fluorination of aliphatic alcohols, with attractive perspectives for rational drug design.Fluorination is commonly exercised in compound property optimization. However, the influence of fluorination on hydrogen-bond (HB) properties of adjacent functional groups, as well as the HB-accepting capacity of fluorine itself, is still not completely understood. Although the formation of OH center dot center dot center dot F intramolecular HBs (IMHBs) has been established for conformationally restricted fluorohydrins, such interaction in flexible compounds remained questionable. Herein is demonstrated for the first time-and in contrast to earlier reports-the occurrence of OH center dot center dot center dot F IMHBs in acyclic saturated g-fluorohydrins, even for the parent 3-fluoropropan-1-ol. The relative stereochemistry is shown to have a crucial influence on the corresponding (h1)J(OH center dot center dot center dot F) values, as illustrated by syn- and anti-4-fluoropentan-2-ol (6.6 and 1.9 Hz). The magnitude of OH center dot center dot center dot F IMHBs and their strong dependence on the overall molecular conformational profile, fluorination motif, and alkyl substitution level, is rationalized by quantum chemical calculations. For a given alkyl chain, the "rule of shielding" applies to OH center dot center dot center dot F IMHB energies. Surprisingly, the predicted OH center dot center dot center dot F IMHB energies are only moderately weaker than these of the corresponding OH center dot center dot center dot OMe. These results provide new insights of the impact of fluorination of aliphatic alcohols, with attractive perspectives for rational drug design.A