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

Abstract

The primary deuterium and tritium isotope effects, δ(XH) − δ(XD/T), were measured for 55 compounds having one or more intramolecular hydrogen bonds. The primary isotope effects were measured at various temperatures. For compounds displaying tautomerism the primary isotope effects are found to have contributions from both intrinsic and equilibrium isotope effects. The primary tritium isotope effect, PΔ(1H,3H), and the primary deuterium isotope effect, PΔ (1H,2H), are shown to be related by This finding is valid for both tautomeric compounds and compounds with localized hydrogen bonds. Large negative primary tritium and deuterium isotope effects were observed for compounds displaying tautomerism and having sulfur as donor or acceptor. These isotope effects show a strong temperature dependence, which is related to the change in equilibrium due to isotope substitution. For the compounds with localized hydrogen bonds, the primary deuterium and tritium isotope effects correlated with the two bond deuterium isotope effect on 13C chemical shifts. The primary deuterium and tritium isotope effects are therefore a measure of the hydrogen bond strength for compounds with localized hydrogen bonds. Copyright © 2000 John Wiley & Sons, Ltd.

A Spectroscopic Overview of Intramolecular Hydrogen Bonds of NH…O,S,N Type

“…Similar values were found for a 4,5-CH2OC as well as the one in which the methyl groups are changed to ethyl groups 2,7-substituted derivatives the values are much smaller, dichloro, dibromo amino, dimethoxy and ditrimethylsilyl gave values of 0.30, 0.23, 0.34, 0.31 [85] The much smaller values in these derivatives were ascribed to a bu leading to a shorter N…N distance [86]. These data and more together with [84] are plotted in Figure 24. Interesting points falling in-between at chemi and 14.84 ppm are N-phenyl derivatives, so these chemical shifts must b ring current effects.…”

“…These data and more together with data from Ref. [ 84 ] are plotted in Figure 24 . Interesting points falling in-between at chemical shifts 14.03 and 14.84 ppm are N-phenyl derivatives, so these chemical shifts must be corrected for ring current effects.…”

“…P ∆ 1 H(ND), and P ∆ 1 H(NT), in which the NH is replaced by either deuterium or tritium may also be used to gauge intramolecular hydrogen bonding. Only a few examples are available [84]. Protonated DMAN's (DMANH + ) (Figure 2) show tautomerism.…”

Isotope Effects on Chemical Shifts in the Study of Intramolecular Hydrogen Bonds

“…A plot including tautomeric compounds like phleichrome [ 75 ], isophleichrome [ 75 ], 2-pivaloylindane-1,3-dione [ 76 ], 5-acetyl-1,3-dimethyl-2,4,6-trioxo-1,3-diazane, 5-acetyl-2,2-dimethyl-4,6-dioxo-1,3-dioxane [ 76 ] and oxo-(2-oxo-cyclohexyl)-acetic acid ethyl ester [ 77 ] but also β-thioxoketones [ 78 ] show that the primary isotope effects may be large and negative ( Figure 20 ). This is typical for a tautomeric system with the two different heavy atoms like O and S as found in β-thioxoketones.…”

H/D isotope effects on the low-temperature NMR parameters and hydrogen bond geometries of (FH)2F−and (FH)3F−dissolved in CDF3/CDF2Cl

“…In particular, the sign of zero-bond (or primary) isotope effect, i.e., the difference between the deuteron and proton hydrogen bond chemical shifts, provides information about the single-or double-well character of the potential function describing the proton motion. [4][5][6][7][8] One-bond isotope effects on the 15 N NMR chemical shifts have been connected to the proton locations in hydrogen-bonded systems of the NÁ Á ÁHÁ Á ÁN type. 9 On the other hand, long-range 13 C isotope shifts have been rationalized in terms of proton transfer equilibria, e.g.…”