Long-range intrinsic and equilibrium deuterium isotope effects on F-19 chemical shifts

Deuterium isotope effects on F-19 chemical shifts caused by deuteriation at OH or NH groups have been determined for intramolecularly hydrogen bonded compounds including fluorinated o-hydroxyacyl aromatics, enaminones, o-hydroxyazo and hydrate compounds. The o-hydroxyazo and hydrate compounds represent tautomeric and non-tautomeric cases. Deuterium isotope effects on fluorine chemical shifts for o-hydroxyacyl aromatics are found to parallel deuterium isotope effects at the carbon ipso to fluorine. For the azo and hydrate compounds very long-range effects are seen formally over ten bonds. Through-space effects are observed in the case of spatially close nuclei like 2-fluorobenzamide-N-alpha. The isotope effects on F-19 chemical shifts can, in p-fluorophenyl substituted cases, be used to monitor the change in equilibrium upon deuteriation and therefore to estimate the importance of hydrogen bonds.