2D Exchange Spectroscopy

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Luis Sánchez - One of the best experts on this subject based on the ideXlab platform.

  • determination of syn anti isomerism in dcnqi derivatives by 2D Exchange Spectroscopy theoretical underpinning
    European Journal of Organic Chemistry, 2000
    Co-Authors: Fernando P. Cossío, Pilar De La Cruz, Antonio De La Hoz, Fernando Langa, Nazario Martín, Pilar Prieto, Luis Sánchez
    Abstract:

    The dynamic syn/anti isomerism resulting from the inversion of the cyano group at the C=N double bond in a series of substituted DCNQIs has been investigated in solution by two-dimensional Exchange Spectroscopy (2D EXSY). The isomers formed were characterised by 1H NMR at 223 K to slow down the inversion process of the cyanoimine group as well as by H,H COSY spectra. Whereas compounds 6, 7, 9 and 10 show only one isomer, compounds 8 and 11 show two isomers with two inversion processes and compounds 12 and 13 show three isomers and four inversion processes. The energy barrier for the syn/anti isomerization of the NCN groups has been estimated from the rate constants determined from the 2D EXSY spectra, and very close values (13.16−13.93 kcal/mol for a single inversion) were found for all compounds. Isomerizations involving two NCN groups (compounds 12 and 13) exhibited higher activation free energy values (13.41−14.40 kcal/mol). Theoretical calculations of these free energy barriers are in excellent agreement with the experimental values, especially when solvent effects are taken into account. Theoretical calculations at B3LYP/6−31G* level predict planar geometries for the DCNQI derivatives studied (6 and 8), in particular when solvent effects are considered. This is in perfect agreement with the experimental data. Two-electron stabilizing interactions, as well as solvent effects, are related to the relative energies of the different stereoisomers. The relative equilibrium populations of the different isomers have been calculated using semiempirical energies and Boltzmann’s distribution. Although the most stable isomer as determined by AM1 method is in qualitative agreement with that deduced from NMR experiments in all DCNQI derivatives studied, better quantitative correlations are obtained at the B3LYP(L1A1)/6−31G* calculation level. Comparison of both semiempirical and ab initio calculations reveal that in these DCNQI systems AM1 is the method of choice for those larger systems whose size prevents energy calculations at higher levels.

  • Determination of syn/anti Isomerism in DCNQI Derivatives by 2D Exchange Spectroscopy: Theoretical Underpinning
    European Journal of Organic Chemistry, 2000
    Co-Authors: Fernando P. Cossío, Pilar De La Cruz, Antonio De La Hoz, Fernando Langa, Nazario Martín, Pilar Prieto, Luis Sánchez
    Abstract:

    The dynamic syn/anti isomerism resulting from the inversion of the cyano group at the C=N double bond in a series of substituted DCNQIs has been investigated in solution by two-dimensional Exchange Spectroscopy (2D EXSY). The isomers formed were characterised by 1H NMR at 223 K to slow down the inversion process of the cyanoimine group as well as by H,H COSY spectra. Whereas compounds 6, 7, 9 and 10 show only one isomer, compounds 8 and 11 show two isomers with two inversion processes and compounds 12 and 13 show three isomers and four inversion processes. The energy barrier for the syn/anti isomerization of the NCN groups has been estimated from the rate constants determined from the 2D EXSY spectra, and very close values (13.16−13.93 kcal/mol for a single inversion) were found for all compounds. Isomerizations involving two NCN groups (compounds 12 and 13) exhibited higher activation free energy values (13.41−14.40 kcal/mol). Theoretical calculations of these free energy barriers are in excellent agreement with the experimental values, especially when solvent effects are taken into account. Theoretical calculations at B3LYP/6−31G* level predict planar geometries for the DCNQI derivatives studied (6 and 8), in particular when solvent effects are considered. This is in perfect agreement with the experimental data. Two-electron stabilizing interactions, as well as solvent effects, are related to the relative energies of the different stereoisomers. The relative equilibrium populations of the different isomers have been calculated using semiempirical energies and Boltzmann’s distribution. Although the most stable isomer as determined by AM1 method is in qualitative agreement with that deduced from NMR experiments in all DCNQI derivatives studied, better quantitative correlations are obtained at the B3LYP(L1A1)/6−31G* calculation level. Comparison of both semiempirical and ab initio calculations reveal that in these DCNQI systems AM1 is the method of choice for those larger systems whose size prevents energy calculations at higher levels.

Antonio De La Hoz - One of the best experts on this subject based on the ideXlab platform.

  • Microwave‐Assisted Synthesis and Dynamic Behaviour of N2,N4,N6‐Tris(1H‐pyrazolyl)‐1,3,5‐triazine‐2,4,6‐triamines
    QSAR & Combinatorial Science, 2005
    Co-Authors: Angel Díaz-ortiz, Antonio De La Hoz, José Elguero, Andrés Moreno, Sergio Moreno, Agustín Jiménez, Ana Sánchez-migallón
    Abstract:

    A series of N 2 ,N 4 ,N 6 -tris(1H-pyrazolyl)-1,3,5-triazine-2,4,6-triamines has been synthesised under microwave irradiation in solvent-free conditions. By reaction of pyrazolylamines with cyanuric chloride and 2-chloro-4,6-diamino-1,3,5-triazines under microwave irradiation, l,3,5-triazine-2,4,6-triamies with symmetrical and asymmetrical substitution, respectively, can be obtained. In the latter case, the procedure can be easily adapted by addition of a small amount of Dimethyl Sulfoxide (DMSO) for the preparation of polymer-supported triazines, with application in supramolecular combinatorial synthesis. At low temperature, the presence of two or four conformers has been detected for symmetrically and asymmetrically substituted derivatives respectively. ID- and 2D-Exchange Spectroscopy studies in various solvents and at different temperatures have been used to determine the equilibrium constants and the activation free energies of the restricted rotation about the amino - triazine bond. A plot of the activation free energy versus temperature shows a good linear correlation and confirms that the same process is present in all of the compounds under investigation.

  • Synthesis, structural determination and dynamic behavior of 2-chloro-4,6-bis(pyrazolylamino)-1,3,5-triazines
    Organic & biomolecular chemistry, 2003
    Co-Authors: Angel Díaz-ortiz, Antonio De La Hoz, José Elguero, Concepción Foces-foces, Andrés Moreno, Sergio Moreno, Ana Sánchez-migallón, Gema Valiente
    Abstract:

    A series of 2-chloro-4,6-bis(pyrazolylamino)-1,3,5-triazines with applications in crystal engineering have been prepared. At low temperature, the presence of two or three isomers has been detected and these assigned to 4,6-diamino-1,3,5-triazine structures on the basis of comparison with model compounds. 2D-Exchange Spectroscopy studies in various solvents and at different temperatures have been used to determine the equilibrium constants and the activation free energies of the restricted rotation about the amino–triazine bond. A plot of the activation free energy versus temperature showed a good linear correlation and confirmed that the same process is present in all of the compounds under investigation. Comparison with model compounds also confirmed both the occurrence of the restricted rotation and the 4,6-diamino-1,3,5-triazine tautomerism for triazines 1–4 in solution. The structure of compound 1 has been determined in the solid state by X-ray crystallography and consists of a 4,6-diamino-1,3,5-triazine structure stabilized by intra and intermolecular hydrogen bonds.

  • determination of syn anti isomerism in dcnqi derivatives by 2D Exchange Spectroscopy theoretical underpinning
    European Journal of Organic Chemistry, 2000
    Co-Authors: Fernando P. Cossío, Pilar De La Cruz, Antonio De La Hoz, Fernando Langa, Nazario Martín, Pilar Prieto, Luis Sánchez
    Abstract:

    The dynamic syn/anti isomerism resulting from the inversion of the cyano group at the C=N double bond in a series of substituted DCNQIs has been investigated in solution by two-dimensional Exchange Spectroscopy (2D EXSY). The isomers formed were characterised by 1H NMR at 223 K to slow down the inversion process of the cyanoimine group as well as by H,H COSY spectra. Whereas compounds 6, 7, 9 and 10 show only one isomer, compounds 8 and 11 show two isomers with two inversion processes and compounds 12 and 13 show three isomers and four inversion processes. The energy barrier for the syn/anti isomerization of the NCN groups has been estimated from the rate constants determined from the 2D EXSY spectra, and very close values (13.16−13.93 kcal/mol for a single inversion) were found for all compounds. Isomerizations involving two NCN groups (compounds 12 and 13) exhibited higher activation free energy values (13.41−14.40 kcal/mol). Theoretical calculations of these free energy barriers are in excellent agreement with the experimental values, especially when solvent effects are taken into account. Theoretical calculations at B3LYP/6−31G* level predict planar geometries for the DCNQI derivatives studied (6 and 8), in particular when solvent effects are considered. This is in perfect agreement with the experimental data. Two-electron stabilizing interactions, as well as solvent effects, are related to the relative energies of the different stereoisomers. The relative equilibrium populations of the different isomers have been calculated using semiempirical energies and Boltzmann’s distribution. Although the most stable isomer as determined by AM1 method is in qualitative agreement with that deduced from NMR experiments in all DCNQI derivatives studied, better quantitative correlations are obtained at the B3LYP(L1A1)/6−31G* calculation level. Comparison of both semiempirical and ab initio calculations reveal that in these DCNQI systems AM1 is the method of choice for those larger systems whose size prevents energy calculations at higher levels.

  • Determination of syn/anti Isomerism in DCNQI Derivatives by 2D Exchange Spectroscopy: Theoretical Underpinning
    European Journal of Organic Chemistry, 2000
    Co-Authors: Fernando P. Cossío, Pilar De La Cruz, Antonio De La Hoz, Fernando Langa, Nazario Martín, Pilar Prieto, Luis Sánchez
    Abstract:

    The dynamic syn/anti isomerism resulting from the inversion of the cyano group at the C=N double bond in a series of substituted DCNQIs has been investigated in solution by two-dimensional Exchange Spectroscopy (2D EXSY). The isomers formed were characterised by 1H NMR at 223 K to slow down the inversion process of the cyanoimine group as well as by H,H COSY spectra. Whereas compounds 6, 7, 9 and 10 show only one isomer, compounds 8 and 11 show two isomers with two inversion processes and compounds 12 and 13 show three isomers and four inversion processes. The energy barrier for the syn/anti isomerization of the NCN groups has been estimated from the rate constants determined from the 2D EXSY spectra, and very close values (13.16−13.93 kcal/mol for a single inversion) were found for all compounds. Isomerizations involving two NCN groups (compounds 12 and 13) exhibited higher activation free energy values (13.41−14.40 kcal/mol). Theoretical calculations of these free energy barriers are in excellent agreement with the experimental values, especially when solvent effects are taken into account. Theoretical calculations at B3LYP/6−31G* level predict planar geometries for the DCNQI derivatives studied (6 and 8), in particular when solvent effects are considered. This is in perfect agreement with the experimental data. Two-electron stabilizing interactions, as well as solvent effects, are related to the relative energies of the different stereoisomers. The relative equilibrium populations of the different isomers have been calculated using semiempirical energies and Boltzmann’s distribution. Although the most stable isomer as determined by AM1 method is in qualitative agreement with that deduced from NMR experiments in all DCNQI derivatives studied, better quantitative correlations are obtained at the B3LYP(L1A1)/6−31G* calculation level. Comparison of both semiempirical and ab initio calculations reveal that in these DCNQI systems AM1 is the method of choice for those larger systems whose size prevents energy calculations at higher levels.

Fernando P. Cossío - One of the best experts on this subject based on the ideXlab platform.

  • determination of syn anti isomerism in dcnqi derivatives by 2D Exchange Spectroscopy theoretical underpinning
    European Journal of Organic Chemistry, 2000
    Co-Authors: Fernando P. Cossío, Pilar De La Cruz, Antonio De La Hoz, Fernando Langa, Nazario Martín, Pilar Prieto, Luis Sánchez
    Abstract:

    The dynamic syn/anti isomerism resulting from the inversion of the cyano group at the C=N double bond in a series of substituted DCNQIs has been investigated in solution by two-dimensional Exchange Spectroscopy (2D EXSY). The isomers formed were characterised by 1H NMR at 223 K to slow down the inversion process of the cyanoimine group as well as by H,H COSY spectra. Whereas compounds 6, 7, 9 and 10 show only one isomer, compounds 8 and 11 show two isomers with two inversion processes and compounds 12 and 13 show three isomers and four inversion processes. The energy barrier for the syn/anti isomerization of the NCN groups has been estimated from the rate constants determined from the 2D EXSY spectra, and very close values (13.16−13.93 kcal/mol for a single inversion) were found for all compounds. Isomerizations involving two NCN groups (compounds 12 and 13) exhibited higher activation free energy values (13.41−14.40 kcal/mol). Theoretical calculations of these free energy barriers are in excellent agreement with the experimental values, especially when solvent effects are taken into account. Theoretical calculations at B3LYP/6−31G* level predict planar geometries for the DCNQI derivatives studied (6 and 8), in particular when solvent effects are considered. This is in perfect agreement with the experimental data. Two-electron stabilizing interactions, as well as solvent effects, are related to the relative energies of the different stereoisomers. The relative equilibrium populations of the different isomers have been calculated using semiempirical energies and Boltzmann’s distribution. Although the most stable isomer as determined by AM1 method is in qualitative agreement with that deduced from NMR experiments in all DCNQI derivatives studied, better quantitative correlations are obtained at the B3LYP(L1A1)/6−31G* calculation level. Comparison of both semiempirical and ab initio calculations reveal that in these DCNQI systems AM1 is the method of choice for those larger systems whose size prevents energy calculations at higher levels.

  • Determination of syn/anti Isomerism in DCNQI Derivatives by 2D Exchange Spectroscopy: Theoretical Underpinning
    European Journal of Organic Chemistry, 2000
    Co-Authors: Fernando P. Cossío, Pilar De La Cruz, Antonio De La Hoz, Fernando Langa, Nazario Martín, Pilar Prieto, Luis Sánchez
    Abstract:

    The dynamic syn/anti isomerism resulting from the inversion of the cyano group at the C=N double bond in a series of substituted DCNQIs has been investigated in solution by two-dimensional Exchange Spectroscopy (2D EXSY). The isomers formed were characterised by 1H NMR at 223 K to slow down the inversion process of the cyanoimine group as well as by H,H COSY spectra. Whereas compounds 6, 7, 9 and 10 show only one isomer, compounds 8 and 11 show two isomers with two inversion processes and compounds 12 and 13 show three isomers and four inversion processes. The energy barrier for the syn/anti isomerization of the NCN groups has been estimated from the rate constants determined from the 2D EXSY spectra, and very close values (13.16−13.93 kcal/mol for a single inversion) were found for all compounds. Isomerizations involving two NCN groups (compounds 12 and 13) exhibited higher activation free energy values (13.41−14.40 kcal/mol). Theoretical calculations of these free energy barriers are in excellent agreement with the experimental values, especially when solvent effects are taken into account. Theoretical calculations at B3LYP/6−31G* level predict planar geometries for the DCNQI derivatives studied (6 and 8), in particular when solvent effects are considered. This is in perfect agreement with the experimental data. Two-electron stabilizing interactions, as well as solvent effects, are related to the relative energies of the different stereoisomers. The relative equilibrium populations of the different isomers have been calculated using semiempirical energies and Boltzmann’s distribution. Although the most stable isomer as determined by AM1 method is in qualitative agreement with that deduced from NMR experiments in all DCNQI derivatives studied, better quantitative correlations are obtained at the B3LYP(L1A1)/6−31G* calculation level. Comparison of both semiempirical and ab initio calculations reveal that in these DCNQI systems AM1 is the method of choice for those larger systems whose size prevents energy calculations at higher levels.

Ben L. Feringa - One of the best experts on this subject based on the ideXlab platform.

  • Toward a switchable molecular rotor. Unexpected dynamic behavior of functionalized overcrowded alkenes
    The Journal of Organic Chemistry, 1997
    Co-Authors: Anne Marie Schoevaars, Wim H. Kruizinga, Robert W. J. Zijlstra, Nora Veldman, A.l. Spek, Ben L. Feringa
    Abstract:

    In an approach toward a photochemically bistable molecular rotor the synthesis of cis-1a and trans-1b isomers of 2-(2,6-dimethylphenyl)-9-(2‘,3‘-dihydro-1‘H-naphtho[2,1-b]thiopyran-1‘-ylidene)-9H-thioxanthene (1), being sterically overcrowded alkenes functionalized with an o-xylyl group as a rotor, is described. The key steps in the synthesis are a Suzuki coupling to attach the xylyl moiety and a diazo-thioketone coupling with subsequent desulfurization to introduce the central olefinic bond in 1. The X-ray structure of cis-1a revealed an anti-folded helical conformation. Dynamic NMR studies on both isomers were performed, to elucidate the kinetics of their rotation processes and to investigate the possibility to control the biaryl rotation by photochemical cis-trans isomerization. A rotation barrier was found by coalescence Spectroscopy for cis-1a:  ΔGc⧧ = 22 ± 1 kcal mol-1 in DMSO-d6. 2D Exchange Spectroscopy (EXSY) showed barriers for cis-1a:  ΔG303⧧ 19.0 ± 0.2 kcal mol-1 and trans-1b:  ΔG303⧧ = 19.7 ±...

Maili Liu - One of the best experts on this subject based on the ideXlab platform.

  • Probing dynamics and mechanism of Exchange process of quaternary ammonium dimeric surfactants, 14-s-14, in the presence of conventional surfactants.
    The journal of physical chemistry. B, 2012
    Co-Authors: Jun Liu, Yan Jiang, Hong Chen, Shizhen Mao, Maili Liu
    Abstract:

    In this Article, we investigated effects of different types of conventional surfactants on Exchange dynamics of quaternary ammonium dimeric surfactants, with chemical formula C14H29N+(CH3)(2)-(CH2)(5)-N+(CH3)(2)C14H29 center dot 2Br(-), or 14-s-14 for short. Two nonionic surfactants, TritonX-100 (TX-100) and polyethylene glycol (23) laurylether (Brij-35), and one cationic surfactant, n-tetradecyltrimethyl ammonium bromide (TTAB), and one ionic surfactant, sodium dodecyl sulfate (SDS) were chosen as typical conventional surfactants. Exchange rates of 14-s-14 (s = 2, 3, and 4) between the micelle form and monomer in solution were detected by two NMR methods: one-dimensional (1D) line shape analysis and two-dimensional (2D) Exchange Spectroscopy (EXSY). Results show that the nonionic surfactants (TX-100 and Brij-35), the cationic surfactant (TTAB), and the ionic surfactant (SDS) respectively accelerated, barely influenced, and slowed the Exchange rate of 14-s-14. The effect mechanism was investigated by the self-diffusion experiment, relaxation time measurements (T-2/T-1), the fluorescence experiment (I-1/I-3) and observed chemical shift variations. Results reveal that, nonionic conventional surfactants (TX-100 and Brij-35) loosened the molecule arrangement and decreased hydrophobic interactions in the micelle, and thus accelerated the Exchange rate of 14-s-14. The cationic conventional surfactant (TTAB) barely changed the molecule arrangement and thus barely influenced the Exchange rate of 14-s-14. The ionic conventional surfactant (SDS) introduced the electrostatic attraction effect, tightened the molecule arrangement, and increased hydrophobic interactions in the micelle, and thus slowed down the Exchange rate of 14-s-14. Additionally, the two-step Exchange mechanism of 14-s-14 in the mixed solution was revealed through interesting variation tendencies of Exchange rates of 14-s-14.

  • NMR study of the dynamics of cationic gemini surfactant 14-2-14 in mixed solutions with conventional surfactants.
    The journal of physical chemistry. B, 2009
    Co-Authors: Yan Jiang, Hong Chen, Shizhen Mao, Maili Liu, Ping-ya Luo
    Abstract:

    Three kinds of conventional surfactants, namely, two nonionic surfactants [polyethylene glycol (23) lauryl ether (Brij-35) and Triton X-100 (TX-100)], one cationic surfactant [n-tetradecyltrimethyl ammonium bromide (TTAB)], and an anionic surfactant [sodium n-dodecyl sulfate (SDS)}, were mixed into the quaternary ammonium gemini surfactant [C(14)H(29)N(+)(CH(3))(2)](2)(CH(2))(2)center dot 2Br(-) (14-2-14) in aqueous solution. The Exchange rate constants between 14-2-14 molecules in the mixed micelles and those in the bulk solution were detected using two nuclear magnetic resonance (NMR) methods: one-dimensional (I D) line shape analysis and two-dimensional (2D) Exchange Spectroscopy (EXSY). The results obtained from these two methods were consistent. Both showed that mixing a nonionic conventional surfactant, either Brij-35 or TX-100, enhanced the Exchange process between the 14-2-14 molecules in the mixed micelles and those in the bulk solution. In contrast, the anionic surfactant SDS and the cationic surfactant TTAB slowed the process slightly.