Theoretical calculations of 1H NMR chemical shifts for nitrogenated compounds in chloroform solution

Abstract

In this work we report DFT and MP2 1H NMR calculations using the GIAO method and TMS as reference, for a series of nitrogenated compounds in chloroform solution to assess the ability of available theoretical models to reproduce experimental 1H NMR spectra measured in CDCl3 solution, focusing on CHn and N-H proton signals which are relevant in conformational analysis studies. The Polarizable Continuum Model (PCM) may not work successfully to predict N-H chemical shifts in solution. Only when a few explicit solvent molecules are used in DFT-PCM-CHCl3 geometry optimizations a good agreement with experimental N-H chemical shifts measured in solution is reached, indicating that this is a reliable computational procedure for the prediction of the full NMR spectra of organic molecules containing N-H group. However, finding adequate DFT optimized solvated solute structures which reproduce well both N-H and CHn proton NMR signals can become a hard-computational task.