Primary tritium and deuterium isotope effects on chemical shifts of compounds having an intramolecular hydrogen bond

The primary deuterium and tritium isotope effects, delta(XH) - delta(XD/T), were measured for 55 compounds having one or more intramolecular hydrogen bonds. The primary isotope effects were measured at various temperatures. F or compounds displaying tautomerism the primary isotope effects are found t o have contributions from both intrinsic and equilibrium isotope effects. T he primary tritium isotope effect, (P)Delta(H-1, H-3), and the primary deut erium isotope effect, (P)Delta(H-1, H-2), shown to be related by (P)Delta(H-1, H-3) = 1.4(P)Delta(H-1, H-2) This finding is valid for both tautomeric compounds and compounds with loca lized hydrogen bonds. Large negative primary tritium and deuterium isotope effects were observed for compounds displaying tautomerism and having sulfu r as donor or acceptor. These isotope effects show a strong temperature dep endence, which is related to the change in equilibrium due to isotope subst itution. For the compounds with localized hydrogen bonds, the primary deute rium and tritium isotope effects correlated with the two bond deuterium iso tope effect on C-13 chemical shifts. The primary deuterium and tritium isot ope effects are therefore a measure of the hydrogen bond strength for compo unds with localized hydrogen bonds. Copyright (C) 2000 John Wiley & Sons, L td.