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Lacerda EG, Kamounah FS, Coutinho K, Sauer SPA, Hansen PE, Hammerich O. Computational Prediction of 1 H and 13 C NMR Chemical Shifts for Protonated Alkylpyrroles: Electron Correlation and Not Solvation is the Salvation. Chemphyschem 2018; 20:78-91. [PMID: 30452112 DOI: 10.1002/cphc.201801066] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Indexed: 12/18/2022]
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.
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Affiliation(s)
- Evanildo G Lacerda
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100, Copenhagen, Denmark.,Instituto de Física da Universidade de São Paulo, CP 66318, 05314-970, São Paulo, SP, Brazil
| | - Fadhil S Kamounah
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100, Copenhagen, Denmark.,Department of Science and Environment, Roskilde University, Universitetsvej 1, DK-4000, Roskilde, Denmark
| | - Kaline Coutinho
- Instituto de Física da Universidade de São Paulo, CP 66318, 05314-970, São Paulo, SP, Brazil
| | - Stephan P A Sauer
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100, Copenhagen, Denmark
| | - Poul Erik Hansen
- Department of Science and Environment, Roskilde University, Universitetsvej 1, DK-4000, Roskilde, Denmark
| | - Ole Hammerich
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100, Copenhagen, Denmark
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Djaouane L, Nessark B, Sibous L. Electrochemical synthesis and surface characterization of (pyrrole+2-methylfuran) copolymer. J Mol Struct 2017. [DOI: 10.1016/j.molstruc.2016.09.076] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Heinze J, Frontana-Uribe BA, Ludwigs S. Electrochemistry of conducting polymers--persistent models and new concepts. Chem Rev 2010; 110:4724-71. [PMID: 20557047 DOI: 10.1021/cr900226k] [Citation(s) in RCA: 632] [Impact Index Per Article: 45.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Jürgen Heinze
- Institute for Physical Chemistry, University of Freiburg, 79104 Freiburg, Germany.
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Buda M, Iordache A, Bucher C, Moutet JC, Royal G, Saint-Aman E, Sessler J. Electrochemical Syntheses of Cyclo[n]pyrrole. Chemistry 2010; 16:6810-9. [DOI: 10.1002/chem.201000043] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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E W, Ohkubo K, Sanchez-Garcia D, Zhang M, Sessler JL, Fukuzumi S, Kadish KM. Electron-Transfer Oxidation Properties of Substituted Bi-, Ter-, and Quaterpyrroles. J Phys Chem B 2007; 111:4320-6. [PMID: 17425356 DOI: 10.1021/jp068717h] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A set of open-chain fully substituted bi-, ter-, and quaterpyrroles bearing analogous substituents in the alpha- and beta-pyrrolic positions were studied as a function of their chain length, subunit number, and size of potential conjugation pathway by means of cyclic voltammetry, EPR, and UV-vis spectroelectrochemistry. A comparison of E1/2 values for the first one-electron abstraction of bipyrrole 1 (1.07 V), terpyrrole 2 (0.67 V), and quaterpyrrole 3 (0.44 V) demonstrate clearly that the longer oligopyrroles are easier to oxidize. A strong absorption band is observed in the visible region when terpyrrole 2 is subject to one-electron oxidation, growing in at 856 nm accompanied by a shoulder at 778 nm. These strong absorptions in the visible region of the spectrum are in sharp contrast with the absence of bands in the red region when the bipyrrole 1 is subject to a similar one-electron oxidation and this can be explained by the presence of a longer conjugation pathway in the singly oxidized forms of 2 as was confirmed by EPR spectroscopy. The EPR spectra of 1*+, 2*+, and 3*+ indicate that the unpaired electron is more delocalized on the pyrroles with a longer conjugation and that the more the unpaired electron is delocalized, the faster is the electron exchange rate.
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Affiliation(s)
- Wenbo E
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
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Heinze J, Rasche A, Pagels M, Geschke B. On the Origin of the So-Called Nucleation Loop during Electropolymerization of Conducting Polymers. J Phys Chem B 2007; 111:989-97. [PMID: 17266253 DOI: 10.1021/jp066413p] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
During the potentiodynamic preparation of conducting polymers, cyclic voltammograms of many pi-conjugated monomers and oligomers often show a marked crossing or loop effect. The so-called "nucleation loop" of the first cycle has been ascribed to the nucleation process requiring an activation energy provided by an overpotential. This paper presents cyclic voltammograms of pi-systems with trace crossing as well as loop effects that suggest that the homogeneous formation of oligomeric redoxactive follow-up products from the starting species is responsible for this occurrence. As the investigated species are typical starting components of resulting oligomers or polymers, all these findings are evidence that similar mechanisms also hold for the formation of many other classical polymers with a "nucleation loop" like polypyrrole, and that the true reason for the nucleation loop is the comproportionation reaction between an oligomeric follow-up product and the starting "monomer".
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Affiliation(s)
- Jürgen Heinze
- Institute of Physical Chemistry and Freiburger Materials Research Center, Albertstrasse 21, D-79104 Freiburg, Germany.
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