Conformational Equilibrium of Cinchonidine in C₆D₁₂ Solution. Alternative NMR/DFT Approach

Area of Science:

• Organic Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Cinchonidine is a complex organic molecule with significant applications.
• Understanding its conformational behavior in solution is crucial for its effective utilization.
• Previous studies utilized NOESY spectra and other physicochemical data.

Purpose of the Study:

• To measure and interpret Nuclear Magnetic Resonance (NMR) parameters for cinchonidine in solution.
• To utilize quantum chemistry calculations to support experimental NMR data.
• To elucidate the conformational equilibrium of cinchonidine.

Main Methods:

• Proton Nuclear Magnetic Resonance (¹H NMR) and Carbon-13 Nuclear Magnetic Resonance (¹³C NMR) spectroscopy.
• Measurement of conformation-dependent vicinal ¹H-¹H spin-spin coupling constants.
• Quantum chemistry calculations using Density Functional Theory (DFT) at the B3LYP/6-311++G(2d,p) level with a polarizable continuum model (PCM).

Main Results:

• Experimental NMR chemical shifts and coupling constants for cinchonidine were accurately reproduced by DFT calculations for key conformers.
• Detailed information on the conformational equilibrium of cinchonidine in C₆D₁₂ solution was obtained.
• The findings align with previous research using NOESY spectra and other data.

Conclusions:

• Quantitative analysis of NMR chemical shifts provides reliable structural insights for complex molecules like cinchonidine.
• NMR spectroscopy, combined with computational methods, offers an independent and valuable approach to structural determination in solution.
• This study validates the power of NMR spectroscopy in characterizing molecular conformations.