Verifying that the structures of synthetic alkaloids match those of natural products is often challenging due to changes in <sup>1</sup>H and <sup>13</sup>C chemical shifts at different pHs of solutions used for recording NMR spectra. We are developing a computational method to determine the degree of protonation for alkaloids in solution by comparing the theoretical chemical shifts for the ammonium and free base forms of alkaloids to the experimental shifts. While combining the theoretical shifts for the two forms of the alkaloids into a weighted average for comparison against the experimental shifts at a given pH creates a new set of chemical shifts closer to the experimental data, predicted shifts were not accurate enough to describe the experimental data. Thus, additional methods of modelling the protonated alkaloids were investigated. DFT calculations were performed at the mPW1PW91/6-311+G(2d,p) (GIAO; PCM, chloroform)//B3LYP-D3(BJ)/6-31G+(d,p) level of theory.

Computational determination of alkaloid chemical shifts with pH change

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.