Structural studies on Mannich bases of 2-Hydroxy-3,4,5,6-tetrachlorobenzene. An UV, IR, NMR and DFT study. A mini-review

•Prediction of OH stretching frequencies based on simple DFT calculations.•Deuterium isotope effects on 13C chemical shifts to reveal tautomerism.•Prediction of isotope effects based on calculated OH bond lengths.

Mannich bases of 2-Hydroxy-3,4,5,6-tetrachlorobenzene are chosen as an exemplary case for tautomeric Mannich bases. Molecular structures are calculated. OH stretching frequencies are rationalized based on DFT calculations. Intrinsic deuterium isotope effects on 13C chemical shifts in the M-form are estimated based on OH bond lengths. The observed deuterium isotope effects on 13C chemical shifts are demonstrated to be largely of equilibrium type except at ambient temperatures.

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