jp8b06722_si_001.pdf (2.09 MB)
Conformational Equilibrium of Cinchonidine in C6D12 Solution. Alternative NMR/DFT Approach
journal contribution
posted on 2018-09-21, 19:45 authored by Sergey Molchanov, Tomasz Rowicki, Adam Gryff-Keller, Wiktor Koźmiński1H NMR and 13C NMR chemical shifts as well
as conformation dependent vicinal 1H–1H spin–spin coupling constants for cinchonidine in a dilute
C6D12 solution have been measured. These data
have been interpreted in detail exploiting the results of the extensive
quantum chemistry calculations of molecular geometry and NMR parameters
of the molecule, performed using the density functional theory (DFT)
B3LYP/6-311++G(2d,p) polarizable continuum model (PCM) level of theory.
The experimental values of NMR parameters for cinchonidine have been
reproduced very well in terms of parameters calculated for key conformers
of this molecule. Simultaneously, the analysis has provided us with
a lot of information on conformational equilibrium of cinchonidine
in the investigated solution. These findings remain in general agreement
with the conclusions of other works, based on NOESY spectra or other
physicochemical data. Thus, a careful quantitative interpretation
of easily measurable NMR chemical shifts can be an independent and
valuable source of structural information even in such complex cases
as cinchonidine in solution.