1
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Modeling through space magnetic shielding over the tetrafluoroborate (BF4−) and tetrachloroborate (BCl4−) anions. J Mol Model 2020; 26:97. [DOI: 10.1007/s00894-020-4351-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Accepted: 03/11/2020] [Indexed: 10/24/2022]
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2
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Ab initio calculation of through-space magnetic shielding of linear polycyclic aromatic hydrocarbons (acenes): Extent of aromaticity. J Mol Graph Model 2009; 27:689-92. [DOI: 10.1016/j.jmgm.2008.10.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2008] [Revised: 09/09/2008] [Accepted: 10/27/2008] [Indexed: 11/20/2022]
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3
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Cyclobutadiene dianion derivatives – Planar 4c,6e or three-dimensional 6c,6e aromaticity? ACTA ACUST UNITED AC 2008. [DOI: 10.1016/j.theochem.2008.05.027] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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4
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Kleinpeter E, Koch A, Seidl PR. Visualization and Quantification of the Anisotropic Effect of C═C Double Bonds on 1H NMR Spectra of Highly Congested Hydrocarbons-Indirect Estimates of Steric Strain. J Phys Chem A 2008; 112:4989-95. [DOI: 10.1021/jp801063t] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Erich Kleinpeter
- Chemisches Institut, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Golm, Germany, and Universidade Federal do Rio de Janeiro, Escola de Química, Centro de Tecnologia, Bloco E, CEP 21949-900, Rio de Janeiro, RJ, Brazil
| | - Andreas Koch
- Chemisches Institut, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Golm, Germany, and Universidade Federal do Rio de Janeiro, Escola de Química, Centro de Tecnologia, Bloco E, CEP 21949-900, Rio de Janeiro, RJ, Brazil
| | - Peter R. Seidl
- Chemisches Institut, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Golm, Germany, and Universidade Federal do Rio de Janeiro, Escola de Química, Centro de Tecnologia, Bloco E, CEP 21949-900, Rio de Janeiro, RJ, Brazil
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5
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Kleinpeter E, Koch A, Sahoo HS, Chand DK. Anisotropic effect of the nitrate anion—manifestation of diamagnetic proton chemical shifts in the 1H NMR spectra of NO3− coordinated complexes. Tetrahedron 2008. [DOI: 10.1016/j.tet.2008.03.063] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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6
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Trisannelated benzenes – Aromatic molecules or 1,3,5-cyclohexatriene derivatives subjected to magnetic properties. ACTA ACUST UNITED AC 2008. [DOI: 10.1016/j.theochem.2008.02.013] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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7
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Martin NH, Floyd RM, Woodcock HL, Huffman S, Lee CK. Computation of through-space NMR shielding effects in aromatic ring π-stacked complexes. J Mol Graph Model 2008; 26:1125-30. [DOI: 10.1016/j.jmgm.2007.10.004] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2007] [Accepted: 10/03/2007] [Indexed: 11/25/2022]
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8
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Kleinpeter E, Klod S, Koch A. Endohedral and External Through-Space Shieldings of the Fullerenes C50, C60, C60-6, C70, and C70-6Visualization of (Anti)Aromaticity and Their Effects on the Chemical Shifts of Encapsulated Nuclei. J Org Chem 2008; 73:1498-507. [DOI: 10.1021/jo702316h] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Erich Kleinpeter
- Chemisches Institut, Universität Potsdam, P.O. Box 60 15 53, D-14415 Potsdam, Germany
| | - Sabrina Klod
- Chemisches Institut, Universität Potsdam, P.O. Box 60 15 53, D-14415 Potsdam, Germany
| | - Andreas Koch
- Chemisches Institut, Universität Potsdam, P.O. Box 60 15 53, D-14415 Potsdam, Germany
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9
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Kleinpeter E, Klod S, Koch A. Visualization of through space NMR shieldings of aromatic and anti-aromatic molecules and a simple means to compare and estimate aromaticity. ACTA ACUST UNITED AC 2007. [DOI: 10.1016/j.theochem.2007.02.049] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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10
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Martin NH, Main KL, Pyles AK. Computation of through-space NMR shielding effects by aromatic ring–cation complexes: Substantial synergistic effect of complexation. J Mol Graph Model 2007; 25:806-12. [PMID: 16959511 DOI: 10.1016/j.jmgm.2006.08.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2006] [Accepted: 08/01/2006] [Indexed: 11/23/2022]
Abstract
The HF-GIAO method in Gaussian 03 was employed to calculate the NMR isotropic shielding values of a diatomic hydrogen probe and to predict the through-space proton NMR shielding increment surfaces above benzene complexed with ammonium, lithium, sodium, potassium, magnesium or calcium ion. The sum of the calculated isotropic shielding values for the proximal hydrogen of a diatomic hydrogen probe over benzene and those calculated at appropriate positions relative to cations were subtracted from the isotropic shielding values calculated for the complexes. The result is a shielding increment for complexation. Complexation results in a synergistic effect on NMR shielding. Enhanced shielding was observed over the pi electron cloud of benzene upon complexation with the cations, more than the sum of the separate effects of the aromatic ring and the charge. The results are interpreted in terms of polarization of the pi cloud of benzene by the cation and its consequences.
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Affiliation(s)
- Ned H Martin
- Department of Chemistry and Biochemistry, University of North Carolina Wilmington, 601 S. College Road, Wilmington, NC 28403-5932, USA.
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11
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Subramaniam G, Karimi S, Phillips D. Solution conformation of longifolene and its precursor by NMR and ab initio calculations. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2006; 44:1118-21. [PMID: 17001750 DOI: 10.1002/mrc.1908] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
We describe the conformation and stereospecific 1H and 13C chemical shift assignments of longifolene 1 and its penultimate precursor 2 through the combined use of ab initio calculations and experimental NMR techniques. The predicted stable conformation for both compounds was similar and adopts a twisted chair conformation at the seven-membered ring where C4 lies on top of the exocyclic double bond. The calculated chemical shifts for the stable conformation agree well with the experimental values.
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Affiliation(s)
- Gopal Subramaniam
- Department of Chemistry and Biochemistry, Queens College of CUNY, Flushing, NY 11367, USA.
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12
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Martin NH, Loveless DM, Main KL, Wade DC. Computation of through-space NMR shielding effects by small-ring aromatic and antiaromatic hydrocarbons. J Mol Graph Model 2006; 25:389-95. [PMID: 16574447 DOI: 10.1016/j.jmgm.2006.02.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2006] [Revised: 02/20/2006] [Accepted: 02/20/2006] [Indexed: 10/25/2022]
Abstract
The GIAO-HF method in Gaussian 03 was employed to calculate the isotropic NMR shielding values of a diatomic hydrogen probe above simple small-ring aromatic and antiaromatic hydrocarbons, including neutral and ionic examples. Subtraction of the isotropic shielding of diatomic hydrogen by itself allowed the prediction of through-space proton NMR shielding increment surfaces for these systems. Substantial shielding was observed above the center of aromatic rings, regardless of whether the ring was pi-aromatic or sigma-aromatic, and also regardless of the charge. In sharp contrast, deshielding was observed above the center of antiaromatic rings, regardless of whether the ring was pi-aromatic or sigma-aromatic, and also regardless of the charge. Shielding increment values at 2.5 angstrom above the ring centers were compared to NICS values at the same position. The shielding effects predicted by using diatomic hydrogen as a computational probe are diagnostic of whether a structure possesses aromaticity or antiaromaticity.
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Affiliation(s)
- Ned H Martin
- Department of Chemistry and Biochemistry, University of North Carolina Wilmington, 601 S. College Road, Wilmington, NC 28403-5932, USA.
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13
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Martin NH, Loveless DM, Main KL, Pyles AK. Computation of through-space NMR shielding effects by functional groups common to peptides. J Mol Graph Model 2006; 25:1-9. [PMID: 16300978 DOI: 10.1016/j.jmgm.2005.10.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2005] [Revised: 10/18/2005] [Accepted: 10/18/2005] [Indexed: 10/25/2022]
Abstract
The GIAO-HF method in Gaussian 03 was employed to calculate the isotropic shielding values of a covalently bonded hydrogen probe and to predict the through-space proton NMR shielding increment surfaces near models of simple structures containing functional groups common to peptides. The functional groups examined include the carboxylate anion, carboxylic acid, amide, amino, ammonium and guanidinium groups. Our previously developed methodology involving the use of diatomic hydrogen as a probe of through-space shielding effects was employed. Substantial shielding or deshielding effects were observed only in the cases of the charged (ionic) groups, each of which displayed shielding or deshielding effects of greater than 1 ppm at distances comparable to those observed in peptides. Equations for predicting the shielding increments of these groups as a function of the Cartesian coordinate position of the affected proton were determined. The validity of using simple structures as models of shielding by comparable functional groups in peptides was confirmed by computing the shielding effects at selected positions above a model of glycylglycylglycine and its hydrogen-bonded dimer. Knowledge of these through-space shielding effects should aid in the tertiary structure determination of peptides by NMR.
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Affiliation(s)
- Ned H Martin
- Department of Chemistry and Biochemistry, University of North Carolina Wilmington, 601 S. College Road, Wilmington, NC 28403-5932, USA
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14
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Martin NH, Loveless DM, Wade DC. A comparison of calculated NMR shielding probes. J Mol Graph Model 2004; 23:285-90. [PMID: 15530824 DOI: 10.1016/j.jmgm.2004.09.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2004] [Revised: 09/20/2004] [Accepted: 09/20/2004] [Indexed: 11/26/2022]
Abstract
In a strong magnetic field, covalently bonded hydrogen nuclei located over the plane of an anisotropic pi bond-containing functional group experience magnetic shielding (or deshielding) that results from the combined effect of the magnetic anisotropy of the functional group and other nearby covalent bonds plus other intramolecular shielding effects. These effects can now be calculated with reasonable accuracy using ab initio methods. We have investigated several computational probes of the magnetic shielding surface near anisotropic functional groups and compared the results to previous reports of experimental observations in example structures. GIAO-HF in Gaussian 03 was employed to calculate isotropic shielding values and to predict the net NMR shielding increment for several computational probes: methane, diatomic hydrogen, a hydrogen atom, a helium atom, or a ghost atom, each held in various positions over simple test molecules (ethene, ethyne, benzene and HCN) that contain the functional groups studied. Also, the effect of performing single point calculations versus constrained geometry-optimized calculations was examined. In addition, the effect of the angle of the orientation of the probe molecule (in the case of CH(4) and H(2)) relative to the pi bond in the test molecule was studied. Finally, the atomic charges in the molecular probes (CH(4) and H(2)) were computed to investigate the nature of the interaction of the probe with the test molecule. The optimal, most economical computational results were obtained using single point calculations of a diatomic hydrogen probe oriented perpendicular to the surface (or axis) of the test molecule.
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Affiliation(s)
- Ned H Martin
- Department of Chemistry and Biochemistry, University of North Carolina at Wilmington, Wilmington, NC 28403-5932, USA.
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15
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Martin NH, Allen NW, Brown JD, Kmiec DM, Vo L. An NMR shielding model for protons above the plane of a carbonyl group. J Mol Graph Model 2003; 22:127-31. [PMID: 12932783 DOI: 10.1016/s1093-3263(03)00152-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Covalently bonded hydrogen nuclei located over the plane of a carbonyl group in a strong magnetic field experience magnetic shielding (or deshielding) that results from the combined effect of the magnetic anisotropy of the carbon-oxygen double bond and various other intramolecular shielding effects. GIAO-HF in Gaussian 98 was employed to calculate isotropic shielding values and to predict the net proton NMR shielding increment for a simple model system: the proximate proton of methane held in various positions over formaldehyde. The net shielding increments of the proximate proton of methane, plotted against its Cartesian coordinates relative to the center of the carbon-oxygen double bond, led to the development of a single empirical equation for predicting the NMR shielding experienced by a covalently bonded proton over the plane of a carbonyl group. The predictive capability of this equation has been validated by calculating the shielding increments of protons over the plane of a carbonyl group in known structures, using this as a correction to the chemical shift estimated by subtituent effects and comparing the result to experimentally observed chemical shifts. Shielding is predicted by this equation for protons located in the region from over the center of the carbon-oxygen double bond to beyond the carbon atom; deshielding is predicted for protons located above and beyond the oxygen atom. This prediction differs from those made by the long-held "shielding cone" model found in nearly every textbook on NMR, but is consistent with experimental observations. The algorithm for predicting the shielding increment for a proton over a carbonyl group can be used in a spreadsheet or incorporated into software that estimates chemical shifts using additive substituent constants or a database of structures. Its use can improve the accuracy of the estimated chemical shift of a proton in the vicinity of a carbon-oxygen double bond, and thus assist in spectral assignments and in correct structure determination.
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Affiliation(s)
- Ned H Martin
- Department of Chemistry, University of North Carolina at Wilmington, Wilmington, NC 28403-5932, USA.
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Packer MJ, Zonta C, Hunter CA. Complexation-induced chemical shifts--ab initio parameterization of transferable bond anisotropies. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2003; 162:102-112. [PMID: 12762987 DOI: 10.1016/s1090-7807(03)00037-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Complexation-induced changes in proton chemical shifts provide a potent tool for conformational analysis, being highly dependent on intermolecular orientation. An important contribution to these shifts arises from the molecular magnetisability anisotropy, or more specifically from the anisotropy of certain groups, such as aromatic rings and unsaturated bonds. While the influence of aromatic rings has been well characterised via the ring current effect, unsaturated bonds have received much less attention and prediction of complexation shifts is hampered by the lack of accurate anisotropy parameters for these bonds. We have therefore used ab initio calculations at the HF/aug-cc-pVDZ level to obtain bond anisotropies for C-H, N-H, C=O, C=C, C triple bond N, N=N, C triple bond C, and C triple bond N. Fitting the anisotropies to bond magnetic dipoles (the McConnell equation) gives non-transferable values for C-H and N-H bonds. We have therefore expanded in terms of bond magnetic dipoles, quadrupoles, and octopoles for double and triple bonds only, obtaining highly accurate shielding surfaces in all cases. The transferable nature of the anisotropies is confirmed by comparing with shifts obtained in larger molecules containing unsaturated bonds.
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Affiliation(s)
- Martin J Packer
- Department of Chemistry, Krebs Institute for Biomolecular Science, University of Sheffield, Sheffield, S3 7HF, England, UK.
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Martin NH, Nance KH. Modeling through-space magnetic shielding over ethynyl, cyano, and nitro groups. J Mol Graph Model 2002; 21:51-6. [PMID: 12413031 DOI: 10.1016/s1093-3263(02)00120-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In a strong magnetic field, covalently bonded hydrogen nuclei located over a pi bonded functional group experience magnetic shielding (or deshielding) that results from the combined effect of the magnetic anisotropy of the pi bond and various other intramolecular shielding effects. Gauge including atomic orbital (GIAO)-HF in Gaussian 98 was employed to calculate isotropic shielding values and to predict the net through-space proton NMR shielding increment for a simple model system: the proximate proton of methane held in various positions over simple molecules that contain a carbon-carbon triple bond, a carbon-nitrogen triple bond, or a nitro group. These net shielding increments of the proximate proton of methane, plotted against their Cartesian coordinates, led to the development of a single empirical equation for predicting the NMR shielding experienced by a covalently bonded proton over each group. The predictive capability of each equation has been validated by calculating shielding increments of protons over the functional group in known structures. These shielding increments are then used to adjust predicted chemical shifts for through-space shielding effects, and the adjusted values are compared to experimentally observed chemical shifts. The algorithms for predicting the shielding increment for a proton over these functional groups can be used in a spreadsheet or incorporated into software that estimates chemical shifts using additive substituent constants or a database of structures. Their use can substantially improve the accuracy of the estimated chemical shift of a proton in the vicinity of these functional groups, and thus assist in spectral assignments and in correct structure determination.
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Affiliation(s)
- Ned H Martin
- Department of Chemistry, University of North Carolina at Wilmington, 28403-5932, USA.
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Martin NH, Brown JD, Nance KH, Schaefer HF, Schleyer PR, Wang ZX, Woodcock HL. Analysis of the origin of through-space proton NMR deshielding by selected organic functional groups. Org Lett 2001; 3:3823-6. [PMID: 11720545 DOI: 10.1021/ol016500u] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
GIAO-HF and IGLO-DFT computations of isotropic magnetic shieldings were used to map the NMR shielding environments of small molecules exemplifying selected organic functional groups. Two different probes were employed: a methane molecule and NICS (nucleus-independent chemical shifts) based on computed absolute isotropic shieldings. The reason for the different results obtained using these two probes is perturbation of the wave function by the proximity of methane to the pi bond, as analyzed by the localized orbital contributions to the shieldings. [structure: see text]
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Affiliation(s)
- N H Martin
- Department of Chemistry, University of North Carolina at Wilmington, Wilmington, NC 28403-5932, USA.
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A New Graphical Model for Proton NMR (De)shielding over a Carbon-Carbon Double Bond to Replace the Shielding Cone Model. Int J Mol Sci 2000. [DOI: 10.3390/ijms1040084] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Martin NH, Allen NW, Moore JC. An algorithm for predicting the NMR shielding of protons over substituted benzene rings. J Mol Graph Model 2000; 18:242-6, 300-1. [PMID: 11021540 DOI: 10.1016/s1093-3263(00)00031-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In a strong magnetic field, hydrogen nuclei located over an aromatic ring experience a reduced magnetic field as a result of the induced magnetic field associated with circulating pi electrons. We used GIAO-SCF, an ab initio subroutine in Gaussian 94 to calculate isotropic shielding values and to determine the proton nuclear magnetic resonance (NMR) shielding increment for a simple model system: methane held at various positions over a substituted benzene ring. The NMR shielding increments experienced by the proximal protons of methane have been mapped as a function of their position X, Y, and Z relative to the center of aniline and, separately, nitrobenzene. A mathematical function of the same form has been fit to the three-dimensional shielding increment surface at each of five distances from the face of each aromatic ring. In addition, a single mathematical equation has been developed for predicting the shielding caused by either substituted aromatic ring. The chemical shifts predicted by using the results of this equation in conjunction with additive substituent increments are compared to observed values.
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Affiliation(s)
- N H Martin
- Department of Chemistry, University of North Carolina at Wilmington, 28403-3297, USA.
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