Journal
JOURNAL OF PHYSICAL CHEMISTRY A
Volume 112, Issue 37, Pages 8767-8774Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jp802894f
Keywords
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Funding
- Argentinian Research Council for Science and Technology [PIP 5119/2004]
- Argentinian Agency for Promotion of Science and Technology [PICT 21604/2004, PAE 22592/2004]
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Both NMR spectroscopic parameters are calculated as a function of the distance d(N-H) of the O center dot center dot center dot H center dot center dot center dot N subsystem of (un- or Z-) substituted ortho-hydroxyaryl Schiff bases, with Z = 4-OMe and 5-Cl. Typical patterns for NMR J couplings and magnetic shieldings, sigma(N) (or the chemical shift delta(N)), are obtained showing that they are reliable sensors from which one can get a deeper insight on the intramolecular proton transfer mechanism. An inflection point is found by representing each NMR spectroscopic parameter as a function of d(N-H) or when the correlation between both parameters is depicted. The analysis of these (cubic) functions shows whether the proton is bound to the oxygen or to the nitrogen atom or is shared by both atoms. In line with these findings, it is possible to predict the position of the proton in the bridge. These theoretical findings are supported by previous experimental measurements. It is shown that nitrogen chemical shift is quite sensitive to substituent effects though (1)J((NH)-N-15) is not. This last parameter depends on d(NH). When correlating both spectroscopic parameters, a previous delta(N) vs (1)J((NH)-N-15) linear dependence is generalized to a cubic dependence which seems to be more reliable. Calculations are based on two state of the art methodologies: DFT-B3LYP and polarization propagators at second order of approach (SOPPA) with large enough basis sets.
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