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Computational Prediction of 1 H and 13 C NMR Chemical Shifts for Protonated Alkylpyrroles: Electron Correlation and Not Solvation is the Salvation
Author(s) -
Lacerda Evanildo G.,
Kamounah Fadhil S.,
Coutinho Kaline,
Sauer Stephan P. A.,
Hansen Poul Erik,
Hammerich Ole
Publication year - 2019
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201801066
Subject(s) - chemical shift , solvation , chemistry , protonation , density functional theory , computational chemistry , polarizable continuum model , molecule , electronic correlation , perturbation theory (quantum mechanics) , solvent effects , proton , solvent , chemical physics , physics , quantum mechanics , organic chemistry , ion
Abstract Prediction of chemical shifts in organic cations is known to be a challenge. In this article we meet this challenge for α‐protonated alkylpyrroles, a class of compounds not yet studied in this context, and present a combined experimental and theoretical study of the 13 C and 1 H chemical shifts in three selected pyrroles. We have investigated the importance of the solvation model, basis set, and quantum chemical method with the goal of developing a simple computational protocol, which allows prediction of 13 C and 1 H chemical shifts with sufficient accuracy for identifying such compounds in mixtures. We find that density functional theory with the B3LYP functional is not sufficient for reproducing all 13 C chemical shifts, whereas already the simplest correlated wave function model, Møller–Plesset perturbation theory (MP2), leads to almost perfect agreement with the experimental data. Treatment of solvent effects generally improves the agreement with experiment to some extent and can in most cases be accomplished by a simple polarizable continuum model. The only exception is the NH proton, which requires inclusion of explicit solvent molecules in the calculation.