An improved statistical approach for conformational analysis from 13C NMR chemical shifts

Abstract In this article we propose an improved statistical approach for the estimation of the mole fraction of each conformer in a given conformational equilibrium from the measured averaged 13C NMR chemical shifts. As each compound has a different number of conformers, an iterative process of fitting (backfitting type) is necessary. In each iteration, two estimates are made, i) fitting to a ridge regression model with equality and inequality constraints and selection of variables for each compound and ii) re-fitting for all compounds. This new procedure leads to consistent results, with low standard error and good p-values, allowing the estimation of the conformational composition for small molecules with a reduced number of conformers.