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Yuan FY, Tang ZY, Huang D, Li W, Wu SQ, Huang JL, Yan XL, Fan RZ, Tang GH, Yin S. Tigliane and rhamnofolane glycosides from Euphorbia wallichii prevent oxidative stress-induced neuronal death in PC-12 cells. Bioorg Chem 2022; 128:106103. [PMID: 35998520 DOI: 10.1016/j.bioorg.2022.106103] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 08/05/2022] [Accepted: 08/15/2022] [Indexed: 11/02/2022]
Abstract
Tigliane and rhamnofolane diterpenoids bearing glycosyl substituents are rarely found in nature. In the current study, seven new tigliane glycosides, euphorwallsides A - G (1-7), and five new rhamnofolane glycosides, euphorwallsides H - L (8-12), were isolated from the whole plants of Euphorbia wallichii. Their structures were elucidated by a combination of spectroscopic, computational, and chemical means. The aglycones of 1-5 represent a rare class of 13-deoxygenated tiglianes, while those of 8-12 represent the first examples of 4-deoxygenated rhamnofolanes. 2, 3, 5, 7, 8, and 12 showed significant neuroprotective effects on sodium nitroprusside (SNP)-induced neuronal death in pheochromocytoma cell line PC-12 at 10 μM, being more active than the clinical drug, edaravone. Mechanistic study revealed that the most active compound, 3, could inhibit reactive oxygen species (ROS) accumulation and restore the mitochondrial membrane potential via modulating the Nrf2 signaling pathway in PC-12 cells.
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Affiliation(s)
- Fang-Yu Yuan
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Zhuo-Ya Tang
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Dong Huang
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Wei Li
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Shu-Qi Wu
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Jia-Luo Huang
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Xue-Long Yan
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Run-Zhu Fan
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Gui-Hua Tang
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China
| | - Sheng Yin
- School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China.
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2
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Krivdin LB. Theoretical calculations of carbon-hydrogen spin-spin coupling constants. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2018; 108:17-73. [PMID: 30538048 DOI: 10.1016/j.pnmrs.2018.10.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Revised: 10/09/2018] [Accepted: 10/11/2018] [Indexed: 06/09/2023]
Abstract
Structural applications of theoretical calculations of carbon-hydrogen spin-spin coupling constants are reviewed covering papers published mainly during the last 10-15 years with a special emphasis on the most notable studies of hybridization, substitution and stereoelectronic effects together with the investigation of hydrogen bonding and intermolecular interactions. The wide scope of different applications of calculated carbon-hydrogen couplings in the structural elucidation of particular classes of organic and bioorganic molecules is reviewed, concentrating mainly on saturated, unsaturated, aromatic and heteroaromatic compounds and their functional derivatives, as well as on natural compounds and carbohydrates. The review is dedicated to Professor Emeritus Michael Barfield in view of his invaluable pioneering contribution to this field.
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Affiliation(s)
- Leonid B Krivdin
- A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, Favorsky St. 1, 664033 Irkutsk, Russia.
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3
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Ghosh A, Chaudhuri P. NMR spin–spin coupling constants in microhydrated ortho-aminobenzoic acid. Mol Phys 2015. [DOI: 10.1080/00268976.2014.955065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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4
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Santos MF, Braga CB, Rozada TC, Basso EA, Fiorin BC. Rotational isomerism of some chloroacetamides: theoretical and experimental studies through calculations, infrared and NMR. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2014; 129:148-156. [PMID: 24727174 DOI: 10.1016/j.saa.2014.02.124] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Revised: 02/04/2014] [Accepted: 02/19/2014] [Indexed: 06/03/2023]
Abstract
The geometries involved in the conformational equilibria of 2,2-dichloro-N-cyclohexyl-N-methyl-acetamide (DCCMA) and 2-chloro-N,N-dicyclohexylacetamide (CDCA) were investigated. Theoretical calculations at the B3LYP/cc-pVDZ level of theory showed that gauche forms (ClCCO) are the most stable and the predominant conformers in isolated phase. Both compounds had the conformational behavior in solvents of different polarities estimated from theoretical calculations with the PCM (Polarizable Continuum Model), at the same level of theory, using infrared data from deconvolution of the carbonyl absorption bands and (13)C NMR spectra. Their IR spectra showed two carbonyl absorptions and that the conformer with the highest dipole moment had its population increased when the most polar solvents were used, in accordance with the theoretical calculation in solution. (1)JCH coupling constants were obtained from their NMR spectra, and revealed that there was population variation of conformers with solvent exchange. Experimental data (NMR and IR) as well as calculations including the solvent effects followed the same trend.
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Affiliation(s)
- Marcela F Santos
- Departamento de Química, Universidade Estadual de Ponta Grossa/UEPG, Av. General Carlos Cavalcanti 4748, 84030-900 Ponta Grossa, PR, Brazil
| | - Carolyne B Braga
- Departamento de Química, Universidade Estadual de Ponta Grossa/UEPG, Av. General Carlos Cavalcanti 4748, 84030-900 Ponta Grossa, PR, Brazil
| | - Thiago C Rozada
- Departamento de Química, Universidade Estadual de Maringá/UEM, Av. Colombo 5790, 87020-900 Maringá, PR, Brazil
| | - Ernani A Basso
- Departamento de Química, Universidade Estadual de Maringá/UEM, Av. Colombo 5790, 87020-900 Maringá, PR, Brazil
| | - Barbara C Fiorin
- Departamento de Química, Universidade Estadual de Ponta Grossa/UEPG, Av. General Carlos Cavalcanti 4748, 84030-900 Ponta Grossa, PR, Brazil.
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Garcías-Morales C, Martínez-Salas SH, Ariza-Castolo A. The effect of the nitrogen non-bonding electron pair on the NMR and X-ray in 1,3-diazaheterocycles. Tetrahedron Lett 2012. [DOI: 10.1016/j.tetlet.2012.04.077] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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7
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Ramalho TC, Pereira DH, Thiel W. Thermal and solvent effects on NMR indirect spin-spin coupling constants of a prototypical Chagas disease drug. J Phys Chem A 2011; 115:13504-12. [PMID: 21995614 DOI: 10.1021/jp201576u] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
NMR J-couplings across hydrogen bonds reflect the static and dynamic character of hydrogen bonding. They are affected by thermal and solvent effects and can therefore be used to probe such effects. We have applied density functional theory (DFT) to compute the NMR (n)J(N,H) scalar couplings of a prototypical Chagas disease drug (metronidazole). The calculations were done for the molecule in vacuo, in microsolvated cluster models with one or few water molecules, in snapshots obtained from molecular dynamics simulations with explicit water solvent, and in a polarizable dielectric continuum. Hyperconjugative and electrostatic effects on spin-spin coupling constants were assessed through DFT calculations using natural bond orbital (NBO) analysis and atoms in molecules (AIM) theory. In the calculations with explicit solvent molecules, special attention was given to the nature of the hydrogen bonds formed with the solvent molecules. The results highlight the importance of properly incorporating thermal and solvent effects into NMR calculations in the condensed phase.
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Affiliation(s)
- Teodorico C Ramalho
- Department of Chemistry, Federal University of Lavras, Lavras, Minas Gerais, Brazil.
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Anizelli PR, Favaro DC, Contreras RH, Tormena CF. Effect of Electronic Interactions on NMR 1JCF and 2JCF Couplings in cis- and trans-4-t-Butyl-2-fluorocyclohexanones and Their Alcohol Derivatives. J Phys Chem A 2011; 115:5684-92. [DOI: 10.1021/jp202592c] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Pedro R. Anizelli
- Chemistry Institute, University of Campinas, Post Office Box 6154, 13084-971 Campinas, SP, Brazil
| | - Denize C. Favaro
- Chemistry Institute, University of Campinas, Post Office Box 6154, 13084-971 Campinas, SP, Brazil
| | - Rubén H. Contreras
- Department of Physics, FCEyN, University of Buenos Aires and IFIBA-CONICET, Buenos Aires, Argentina
| | - Cláudio F. Tormena
- Chemistry Institute, University of Campinas, Post Office Box 6154, 13084-971 Campinas, SP, Brazil
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Contreras RH, dos Santos FP, Ducati LC, Tormena CF. Difference between ²JC2H3 and ²JC3H2 spin-spin couplings in heterocyclic five- and six-membered rings as a probe for studying σ-ring currents: a quantum chemical analysis. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2010; 48 Suppl 1:S151-S158. [PMID: 21104760 DOI: 10.1002/mrc.2669] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Adequate analyses of canonical molecular orbitals (CMOs) can provide rather detailed information on the importance of different σ-Fermi contact (FC) coupling pathways (FC term transmitted through the σ-skeleton). Knowledge of the spatial distribution of CMOs is obtained by expanding them in terms of natural bond orbitals (NBOs). Their relative importance for transmitting the σ-FC contribution to a given spin-spin coupling constants (SSCCs) is estimated by resorting to the expression of the FC term given by the polarisation propagator formalism. In this way, it is possible to classify the effects affecting such couplings in two different ways: delocalisation interactions taking place in the neighbourhood of the coupling nuclei and 'round the ring' effects. The latter, associated with σ-ring currents, are observed to yield significant differences between the FC terms of (2)J(C2H3) and (2)J(C3H2) SSCCs which, consequently, are taken as probes to gauge the differences in σ-ring currents for the five-membered rings (furan, thiophene, selenophene and pyrrol) and also for the six-membered rings (benzene, pyridine, protonated pyridine and N-oxide pyridine) used in the present study.
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Affiliation(s)
- Rubén H Contreras
- Department of Physics, FCEyN, University of Buenos Aires and IFIBA-CONICET, Buenos Aires, Argentina
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Kadlecek S, Emami K, Ishii M, Rizi R. Optimal transfer of spin-order between a singlet nuclear pair and a heteronucleus. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2010; 205:9-13. [PMID: 20427216 PMCID: PMC2885468 DOI: 10.1016/j.jmr.2010.03.004] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2010] [Revised: 02/26/2010] [Accepted: 03/03/2010] [Indexed: 05/12/2023]
Abstract
Intramolecular spin-order transfer is a useful technique for signal enhancement of insensitive and low-concentration molecular species. We present a closed-form, optimized pulse sequence which maximizes the efficiency of transfer between a singlet (para) nuclear pair and a vicinal heteronucleus. Neglecting the decay of coherences while the nuclei are in the transverse plane, the scheme is unity efficient for all combinations of internuclear scalar couplings. Efficiency loss due to T2-like decay is also minimized by keeping the sequence as short as possible. We expect this result to be useful for hyperpolarization experiments in which the spin-order originates in parahydrogen, as well as studies of singlet state decay aimed at longer-term storage of spin-order in hyperpolarized Magnetic Resonance Imaging.
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Affiliation(s)
- Stephen Kadlecek
- Department of Radiology, University of Pennsylvania, B-1 Stellar-Chance Labs, 422 Curie Blvd., Philadelphia, PA, USA, 19104, 215-662-6775
| | - Kiarash Emami
- Department of Radiology, University of Pennsylvania, B-1 Stellar-Chance Labs, 422 Curie Blvd., Philadelphia, PA, USA, 19104, 215-662-6775
| | - Masaru Ishii
- Department of Otolaryngology, Johns Hopkins University, 601 N. Caroline St., 6 floor, Baltimore, MD, USA, 21287, 410-955-1080
| | - Rahim Rizi
- Department of Radiology, University of Pennsylvania, B-1 Stellar-Chance Labs, 422 Curie Blvd., Philadelphia, PA, USA, 19104, 215-662-6775
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Contreras RH, Provasi PF, dos Santos FP, Tormena CF. Stereochemical dependence of NMR geminal spin-spin coupling constants. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2009; 47:113-120. [PMID: 18991325 DOI: 10.1002/mrc.2359] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
In this work it was sought to explore the versatility of geminal spin-spin coupling constants, (2)J(XY) SSCCs, as probes for stereochemical studies. A set of compounds, where their experimental (2)J(XY) SSCCs through the X-C-Y molecular fragment are predicted to be sensitive to hyperconjugative interactions involving either bonding or antibonding orbitals containing the C carbon atom ('coupling pathway'), were analyzed. SSCC calculations were performed for some selected examples using the second order polarization propagator approximation (SOPPA) method or within the DFT-B3LYP framework. Hyperconjugative interactions were calculated within the Natural Bond Orbital (NBO) approach. Results are condensed in two qualitative rules: Rule I(M)-hyperconjugative interactions transferring charge into the coupling pathway yield a positive increase to the Fermi contact (FC), contribution to (2)K(XY) reduced spin-spin coupling constants (RSSCC), and Rule II(M)-hyperconjugative interactions transferring charge from the coupling pathway yield a negative increase to the FC contribution to (2)K(XY) RSSCC.
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Affiliation(s)
- Rubén H Contreras
- Department of Physics, FCEyN, University of Buenos Aires and CONICET, Buenos Aires, Argentina
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Relationship between calculated NMR data and intermolecular hydrogen bond properties in X-pyridine⋯HF. Chem Phys 2009. [DOI: 10.1016/j.chemphys.2008.11.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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13
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Cybulski H, Sadlej J. A computational study of the nuclear magnetic resonance parameters for double proton exchange pathways in the formamide–formic acid and formamide–formamidine complexes. Phys Chem Chem Phys 2009; 11:11232-42. [DOI: 10.1039/b913947h] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Pedersoli S, Tormena CF, dos Santos FP, Contreras RH, Rittner R. Stereochemical behavior of 1JCH and 2JCH NMR coupling constants in α-substituted acetamides. J Mol Struct 2008. [DOI: 10.1016/j.molstruc.2008.04.040] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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15
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Pérez C, Suardíaz R, Ortiz PJ, Crespo-Otero R, Bonetto GM, Gavín JA, García de la Vega JM, San Fabián J, Contreras RH. On the unusual 2J(C2-H(f)) coupling dependence on syn/anti CHO conformation in 5-X-furan-2-carboxaldehydes. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2008; 46:846-850. [PMID: 18566984 DOI: 10.1002/mrc.2268] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A remarkable difference for (2)J(C(2)-H(f)) coupling constant in syn and anti conformers of 5-X-furan-2-carboxaldehydes (X = CH(3), Ph, NO(2), Br) and a rationalization of this difference are reported. On the basis of the current knowledge of the Fermi-contact term transmission, a rather unusual dual-coupling pathway in the syn conformer is presented. The additional coupling pathway resembles somewhat that of the J(H-H) in homoallylic couplings, which are transmitted by hyperconjugative interactions involving the pi(C=C) electronic system. The homoallylic coupling pathway can be labeled as sigma*(C-H) <-- pi(C=C) --> sigma*(C-H). In the present case, this additional coupling pathway, using an analogous notation, can be labeled as sigma*(C(2)-C(C)) <-- LP(1)(O(1))...LP(2)(O(C)) --> sigma*(C(C)-H(f)) (sigma*(C(2)-C(C))) where O(1) and O(C) stand for the ring and carbonyl O atoms, respectively. This additional coupling pathway is not activated in the anti conformers since both oxygen lone pairs do not overlap.
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Affiliation(s)
- Carlos Pérez
- Departamento de Química Física, Facultad de Química, Universidad de La Habana, La Habana 10400, Cuba.
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Contreras RH, Suardíaz R, Pérez C, Crespo-Otero R, San Fabián J, García de la Vega JM. Karplus Equation for 3JHH Spin−Spin Couplings with Unusual 3J(180°) < 3J(0°) Relationship. J Chem Theory Comput 2008; 4:1494-500. [DOI: 10.1021/ct800145h] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- R. H. Contreras
- Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and CONICET, Buenos Aires, Argentina, Departamento de Química Física, Facultad de Química, Universidad de la Habana, La Habana 10400, Cuba, and Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - R. Suardíaz
- Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and CONICET, Buenos Aires, Argentina, Departamento de Química Física, Facultad de Química, Universidad de la Habana, La Habana 10400, Cuba, and Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - C. Pérez
- Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and CONICET, Buenos Aires, Argentina, Departamento de Química Física, Facultad de Química, Universidad de la Habana, La Habana 10400, Cuba, and Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - R. Crespo-Otero
- Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and CONICET, Buenos Aires, Argentina, Departamento de Química Física, Facultad de Química, Universidad de la Habana, La Habana 10400, Cuba, and Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - J. San Fabián
- Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and CONICET, Buenos Aires, Argentina, Departamento de Química Física, Facultad de Química, Universidad de la Habana, La Habana 10400, Cuba, and Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - J. M. García de la Vega
- Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and CONICET, Buenos Aires, Argentina, Departamento de Química Física, Facultad de Química, Universidad de la Habana, La Habana 10400, Cuba, and Departamento de Química Física Aplicada, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049 Madrid, Spain
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Suardíaz R, Pérez C, García de la Vega JM, Fabián JS, Contreras RH. Theoretical Karplus relationships for vicinal coupling constants around χ1 in Valine. Chem Phys Lett 2007. [DOI: 10.1016/j.cplett.2007.05.049] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Tormena CF, Vilcachagua JD, Karcher V, Rittner R, Contreras RH. Experimental and theoretical investigation of NMR 2JHH coupling constant on six-membered ring systems containing oxygen or sulfur atoms. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2007; 45:590-4. [PMID: 17534874 DOI: 10.1002/mrc.2014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Theoretical and experimental 2JHH coupling constants for six-membered rings containing oxygen or sulfur atoms were studied to investigate whether the 2JHH coupling constant can be used for stereoelectronic studies in heterocyclohexanes, instead of 1JCH, because it is well known that experimental measurements of 2JHH coupling constants at low temperature are much easier to determine than the corresponding 1JCH couplings. For all compounds studied here, the 2JHH coupling constants are affected by sigma*C-H antibonding occupancy together with bond angle effects. For cyclohexane and oxygen-containing compounds, the influence on the geminal coupling for Hax-C2-Heq and for X1-C2-X3 (X=O and C), bond angles are more pronounced than for the sulfur derivatives.
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Affiliation(s)
- Cláudio F Tormena
- Chemistry Institute, State University of Campinas, Caixa Postal 6154 CEP:13084-971, Campinas, São Paulo, Brazil.
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Investigation of the stereoelectronic properties in 1,2-difluorocyclopropane and 1,2-difluorocyclohexane: Evaluation of the gauche effect. ACTA ACUST UNITED AC 2007. [DOI: 10.1016/j.theochem.2006.12.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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20
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Gauze GF, Tormena R, Basso EA, Tormena CF. Stereoelectronic interactions and their effects on conformational preference for 1,3-dithiane-1-oxide and 1,4-dithiane-1-oxide. A theoretical and experimental study. Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.05.075] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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21
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Contreras RH, Esteban ÁL, DÍez E, Head NJ, Della EW. Transmission mechanisms of NMR long-range J(13C,19F) scalar couplings in 1-F,4-X-cubanes: a DFT and experimental study. Mol Phys 2006. [DOI: 10.1080/00268970500276499] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Gupta N, Shah KK, Garg R. Substituent-dependent anomeric effects as a source of conformational preference in pyridinium methylides. J Org Chem 2006; 71:1344-50. [PMID: 16468781 DOI: 10.1021/jo051852q] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
A systematic density functional theory level investigation of differently substituted pyridinium methylides was carried out to determine the role of C(ylidic) lone-pair-associated hyperconjugative and negative hyperconjugative interactions in deciding conformational preferences. Deviation from the coplanar orientation of the carbanionic center with the pyridine ring and its substituent dependence has been found to correlate well with the relative opportunities for conjugative and negative hyperconjugative interactions of a ylidic moiety with different substituent groups present at the ylidic carbon. The contribution of individual n-->pi* conjugative, n-->sigma* negative hyperconjugative, and sigma-->pi* hyperconjugative interactions in a particular conformation of pyridinium dichlorophosphinomethylides was assessed from donor-acceptor stabilization energies, as obtained from natural bond orbital (NBO) analysis. The relative extent of conjugative and negative hyperconjugative interactions with the substituents present at the ylidic carbon plays an important role in permitting the delocalization of ylidic charge into the pyridine ring, thereby controlling the relative orientation of the latter with the carbanionic plane.
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Affiliation(s)
- Neelima Gupta
- Department of Chemistry, University of Rajasthan, Jaipur-302 004, India.
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Taurian OE, De Kowalewski DG, Pérez JE, Contreras RH. NMR J(13C,13C) spin–spin coupling constants in pyridine-carboxaldehydes. Experimental and DFT-B3LYP studies. J Mol Struct 2005. [DOI: 10.1016/j.molstruc.2005.06.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Tormena CF, Dias LC, Rittner R. Orbital Interactions and Their Effects on 13C NMR Chemical Shifts for 4,6-Disubstituted-2,2-dimethyl-1,3-dioxanes. A Theoretical Study. J Phys Chem A 2005; 109:6077-82. [PMID: 16833944 DOI: 10.1021/jp052048a] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A theoretical study is employed to describe the orbital interactions involved in the conformers' stability, the energies for the stereoelectronic interactions, and the corresponding effects of these interactions on the molecular structure (bond lengths) for cis- and trans-4,6-disubstituted-2,2-dimethyl-1,3-dioxanes. For cis-4,6-disubstituted-2,2-dimethyl-1,3-dioxanes, two LPO --> sigma*C(2)-Me(8) interactions are extremely important and the energies involved in these interactions are in the range 6.81-7.58 kcal mol(-1) for the LP(O)(1) --> sigma*C(2)-Me(8) and 7.58-7.71 kcal mol(-1) for the LP(O)(3) --> sigma*C(2)-Me(8) interaction. These two LP(O) --> sigma*C(2)-Me(8) interactions cause an upfield shift, indicating an increased shielding (increased electron density) of the ketal carbon C(2) as well as the axial Me(8) group in the chair conformation. These LP(O) --> sigma*C(2)-Me(8) hyperconjugative anomeric type interactions can explain the 13C NMR chemical shifts at 19 ppm for the axial methyl group "Me(8)" and 98.5 ppm for the ketal carbon "C(2)". The observed results for the trans derivatives showed that for compounds 2a-c (R = -CN, -C[triple bond]CH, and -CHO, respectively) the chair conformation is predominant, whereas for 2d,f-h [-CH3, -Ph, -C6H4(p-NO2), -C6H4(p-OCH3), respectively] the twist-boat is the most stable compound and for 2e [-C(CH3)3] is the only form.
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Affiliation(s)
- Claudio F Tormena
- Departamento de Química, Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Universidade de São Paulo (USP), Av. Bandeirantes, 3900, 14040-901, Ribeirão Preto SP, Brazil.
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Theoretical NMR nJ(13C,13C) Scalar Couplings as Probes to Study Diamagnetic Ring Currents in Fullerenes. ADVANCES IN QUANTUM CHEMISTRY 2005. [DOI: 10.1016/s0065-3276(05)48009-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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