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Tormena CF. Conformational analysis of small molecules: NMR and quantum mechanics calculations. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2016; 96:73-88. [PMID: 27573182 DOI: 10.1016/j.pnmrs.2016.04.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Revised: 04/14/2016] [Accepted: 04/14/2016] [Indexed: 06/06/2023]
Abstract
This review deals with conformational analysis in small organic molecules, and describes the stereoelectronic interactions responsible for conformational stability. Conformational analysis is usually performed using NMR spectroscopy through measurement of coupling constants at room or low temperature in different solvents to determine the populations of conformers in solution. Quantum mechanical calculations are used to address the interactions responsible for conformer stability. The conformational analysis of a large number of small molecules is described, using coupling constant measurements in different solvents and at low temperature, as well as recent applications of through-space and through-hydrogen bond coupling constants JFH as tools for the conformational analysis of fluorinated molecules. Besides NMR parameters, stereoelectronic interactions such as conjugative, hyperconjugative, steric and intramolecular hydrogen bond interactions involved in conformational preferences are discussed.
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Affiliation(s)
- Cláudio F Tormena
- Institute of Chemistry, University of Campinas, PO Box 6154, 13083-970 Campinas, Sao Paulo, Brazil.
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de Melo UZ, Silva RGM, Yamazaki DAS, Pontes RM, Gauze GF, Rosa FA, Rittner R, Basso EA. NMR spectroscopy and theoretical calculations in the conformational analysis of 1-methylpyrrolidin-2-one 3-halo-derivatives. J Phys Chem A 2015; 119:2111-21. [PMID: 25679501 DOI: 10.1021/jp512378g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This study reports the results of ab initio and density functional theory (DFT) electronic structure calculations as well as (3)J(HH) experimental and calculated coupling constant data obtained in the investigation of the conformational equilibrium of 3-halo-derivatives of 1-methylpyrrolidin-2-one. The five-membered ring assumes an envelope conformation owing to the plane of formation of the O═C-N-R bond, with C4 forming the "envelope lid". When the conformation changes, the "lid" alternates between positions above and below the amide plane. The α-carbonyl halogen assumes two positions: a pseudo-axial and a pseudo-equatorial. In the gaseous phase, the calculations indicate that the pseudo-axial conformer is more stable and preferable going down the halogen family. Natural bond orbital analysis showed that electronic delocalization is significant only for the iodo derivative. In the other derivatives, the electrostatic repulsion between oxygen and the halogen determines the conformational equilibrium. When the solvated molecule was taken into account, the pseudo-equatorial conformer population increased with the relative permittivity of the solvent. This variation was strong in the fluoro derivative, and the preference was inverted. In the chlorine derivative, the two populations became closer in methanol and acetonitrile. In the bromine and iodine derivatives, the percentage of pseudo-equatorial conformer increased only slightly owing to the dipole moment of the conformation: the pseudo-equatorial conformation has a greater dipole moment and thus is stable in media with high relative permittivity.
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Affiliation(s)
- Ulisses Zonta de Melo
- Chemistry Department, State University of Maringa , Avenida Colombo, 5790, 87020-900, Maringa, Paraná, Brazil
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Lomas JS. 1H NMR spectra of ethane-1,2-diol and other vicinal diols in benzene: GIAO/DFT shift calculations. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2013; 51:32-41. [PMID: 23169263 DOI: 10.1002/mrc.3899] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Revised: 10/16/2012] [Accepted: 10/16/2012] [Indexed: 06/01/2023]
Abstract
The proton NMR spectra of several 1,2-diols in benzene have been analysed so as to associate each magnetically nonequivalent proton with its chemical shift. The shifts and coupling constants of the OH and methylene protons of ethane-1,2-diol have been determined in a wide range of solvents. The conformer distribution and the proton NMR shifts of these 1,2-diols in benzene have been computed on the basis of density functional theory. The solvent is included using the integral-equation-formalism polarizable continuum model implemented in Gaussian 09. Relative Gibbs energies for all stable conformers are calculated at the Perdew, Burke and Enzerhof (PBE)0/6-311 + G(d,p) level, and shifts are calculated using the gauge-including atomic orbital method with the PBE0/6-311 + G(d,p) geometry but using the cc-pVTZ basis set. Previous calculations on ethane-1,2-diol and propane-1,2-diol have been corrected and extended. New calculations on tert-butylethane-1,2-diol, phenylethane-1,2-diol, butane-2,3-diols (dl and meso) and cyclohexane-1,2-diols (cis and trans) are presented. Overall, the computed NMR shifts are in good agreement with experimental values for the OH protons but remain systematically high for CH protons. Some results based on the Gaussian 03 solvation model are included for comparison.
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Affiliation(s)
- John S Lomas
- ITODYS, Université Paris Diderot, Sorbonne Paris Cité, UMR 7086, F-75205, Paris, France
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Gauze GF, Basso EA, Contreras RH, Tormena CF. Effect of Sulfur Oxidation on the Transmission Mechanism of 4JHH NMR Coupling Constants in 1,3-Dithiane. J Phys Chem A 2009; 113:2647-51. [DOI: 10.1021/jp810981z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Gisele F. Gauze
- Departamento de Química, Universidade Estadual de Maringá, CEP-87020-900, Maringá, PR, Brazil, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina, and Department of Organic Chemistry, Chemistry Institute, P.O. Box 6154, University of Campinas, UNICAMP, CEP: 13084-971 Campinas, SP, Brazil
| | - Ernani A. Basso
- Departamento de Química, Universidade Estadual de Maringá, CEP-87020-900, Maringá, PR, Brazil, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina, and Department of Organic Chemistry, Chemistry Institute, P.O. Box 6154, University of Campinas, UNICAMP, CEP: 13084-971 Campinas, SP, Brazil
| | - Rubén H. Contreras
- Departamento de Química, Universidade Estadual de Maringá, CEP-87020-900, Maringá, PR, Brazil, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina, and Department of Organic Chemistry, Chemistry Institute, P.O. Box 6154, University of Campinas, UNICAMP, CEP: 13084-971 Campinas, SP, Brazil
| | - Cláudio F. Tormena
- Departamento de Química, Universidade Estadual de Maringá, CEP-87020-900, Maringá, PR, Brazil, Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina, and Department of Organic Chemistry, Chemistry Institute, P.O. Box 6154, University of Campinas, UNICAMP, CEP: 13084-971 Campinas, SP, Brazil
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