Secondary Isotope Effects on C-13 and N-15 Chemical Shifts of Schiff Bases Revisited

作者：Filarowski Alexander; Hansen Poul Erik^*

来源：Zeitschrift fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics, 2013, 227(6-7): 917-927.

DOI：10.1524/zpch.2013.0378

• Secondary Deuterium Isotope Effects
• Chemical Shifts
• Schiff Bases
• DFT Calculations
• Intramolecular Hydrogen Bonding

An analysis is presented of secondary deuterium isotope effects on N-15 and C-13 chemical shifts of the methylamine Schiff base of 4,6-dimethoxysalicylaldehyde. It is shown that for this compound existing as an equilibrium between an OH and a NH-form, the secondary isotope effects depend on the OH/NH ratio giving a function with a maximum and a minimum.
Secondary deuterium isotope effects on C-13 and N-15 chemical shifts are compared in a broader range of compounds and the above trend is confirmed. Changes in the dielectric constants of the medium with temperature are found to be rather unimportant for the change in equilibrium. Equilibrium isotope effects on chemical shifts are shown to be important. The magnitudes of the isotope effects are correlated both to intrinsic and equilibrium isotope effects. The latter correlate to the shape of the two-potential well, the energy difference and the difference in chemical shifts of the two tautomers.

• 出版日期2013