Computational prediction of the ¹H and ¹³C NMR chemical shifts for protonated alkylpyrroles: electron correlation and not solvation is the salvation

TY - JOUR

T1 - Computational prediction of the 1H and 13C NMR chemical shifts for protonated alkylpyrroles

T2 - electron correlation and not solvation is the salvation

AU - Lacerda Jr., Evanildo Gomes

AU - Kamounah, Fadhil S

AU - Coutinho, Kaline

AU - Sauer, Stephan P. A.

AU - Hansen, Poul Erik

AU - Hammerich, Ole

PY - 2019/1/7

Y1 - 2019/1/7

N2 - 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.

AB - 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.

KW - Faculty of Science

KW - MP2

KW - B3LYP

KW - Solvent effects

KW - density functional theory (DFT)

KW - NMR

KW - chemical shift

KW - protonated alkylpyrroles

U2 - 10.1002/cphc.201801066

DO - 10.1002/cphc.201801066

M3 - Journal article

C2 - 30452112

SN - 1439-4235

VL - 20

SP - 78

EP - 91

JO - ChemPhysChem

JF - ChemPhysChem

IS - 1

ER -