The Experts below are selected from a list of 480 Experts worldwide ranked by ideXlab platform
Rui Fausto - One of the best experts on this subject based on the ideXlab platform.
-
Missing conformers. Comparative study of conformational cooling in cyanoacetic acid and Methyl Cyanoacetate isolated in low temperature inert gas matrixes
Chemical Physics Letters, 2003Co-Authors: Igor Reva, Stepan G. Stepanian, Ludwik Adamowicz, Rui FaustoAbstract:Abstract A comparative conformational study of two related systems, Methyl Cyanoacetate (MCA) and cyanoacetic acid (CAA), is presented. Ab initio calculations predicted that both systems have two nearly isoenergetic conformers separated by similar low energy barriers (about 3 kJ mol −1 ). In xenon matrixes deposited at temperatures above 40 K for MCA and above 20 K for CAA only one conformer was observed for each of the two systems. However, below those temperatures two MCA and two CAA conformers were trapped into the matrixes. Conformational cooling was found responsible for this behavior. Factors contributing to this effect are discussed.
-
Conformational isomerism in Methyl Cyanoacetate: A combined matrix-isolation infrared spectroscopy and molecular orbital study
Physical Chemistry Chemical Physics, 2001Co-Authors: Igor Reva, Sonia Ilieva, Rui FaustoAbstract:Study of the conformational isomerism of Methyl Cyanoacetate (NCCH2COOCH3, MCA) aided for the first time by matrix-isolation infrared spectroscopy is reported. The conformational isomerization processes in MCA in the temperature range from 10 to 70 K were studied in detail in argon and xenon matrixes. During annealing of the matrixes direct interconversion of the gauche into the syn conformer has been registered. A similar, but more pronounced, gauche → syn interconversion effect was observed in a series of experiments in which matrixes were deposited at increased substrate temperature. The experiment is supported by theoretical predictions undertaken at different levels of approximation (MP2 and DFT/B3LYP). It is shown that, for the single molecule in vacuum, the syn conformer (C–C–CO dihedral angle equal to 0°) corresponds to the conformational ground state, with the doubly degenerated by symmetry gauche conformer (C–C–CO dihedral angle equal to ± 139.9°) being only slightly less stable than the most stable form (MP2/6-31G** ΔE(gauche → syn) = 0.174 kJ mol−1). In the matrixes, the energy gap between the syn and gauche conformers increases, with ΔE(gauche → syn) estimated to be about 1.4 kJ mol−1 in xenon. The predicted energy barriers for conformer interconversion were found to be significantly low: the MP2/6-31G** calculated ΔE(syn → gauche) energy barrier is ca. 3.65 kJ mol−1, while the calculated energy barrier separating the two symmetrically equivalent gauche conformers stays only 0.196 kJ mol−1 above the energy of these forms. In the matrixes, ΔE(syn → gauche) energy barrier increases to at least 17–18 kJ mol−1, while the ΔE(gauche → gauche) energy barrier is, with all probability, still lower than in the gaseous phase. The matrix isolation spectroscopic data indicate that interconversion between the gauche conformers occurs even in the low temperature matrixes.
-
molecular structure and vibrational spectra of Methyl Cyanoacetate an ft ir raman and ab initio molecular orbital study
Journal of Molecular Structure, 1998Co-Authors: Joao Miguel F Neta, Rui FaustoAbstract:Abstract The results of a combined vibrational and structural study of Methyl Cyanoacetate undertaken by Raman and infrared spectroscopy, and ab initio SCF-MO calculations are presented. It is shown that for the isolated molecule situation, as well as in the liquid phase, Methyl Cyanoacetate exists as a mixture of two main conformers of similar energies, differing by the relative orientation of the NCCCO axis (the syn and skew forms, having a NCCCO dihedral angle equal to 0° and in the ± 140° region, respectively). In the crystalline state, only the thermodynamically most stable syn conformer remains. The ab initio SCF-MO optimized geometries of the various possible conformers, their relative stabilities, dipole moments and harmonic force-fields are presented, and the conformational dependence of some relevant structural parameters is used to characterise the most important intramolecular interactions present in the various forms studied. Finally, results of a normal mode analysis based on the ab initio calculated vibrational spectra are used to help interpret the experimental vibrational data, enabling a detailed assignment of both Raman and infrared spectra.
Jae Nyoung Kim - One of the best experts on this subject based on the ideXlab platform.
-
construction of 1 2 5 tricarbonyl compounds using Methyl Cyanoacetate as a glyoxylate anion synthon combined with copper i iodide catalyzed aerobic oxidation
ChemInform, 2012Co-Authors: Se Hee Kim, Ko Hoon Kim, Jae Nyoung KimAbstract:A variety of α-cyano-δ-ketocarboxylates (I) and (III), obtained by conjugate addition of Cyanoacetate towards α,β-unsaturated ketones, is efficiently oxidized to the corresponding α,δ-diketo esters (II) and (IV), respectively.
-
facile regiocontrolled three step synthesis of poly substituted furans pyrroles and thiophenes consecutive michael addition of Methyl Cyanoacetate to α β enone cui mediated aerobic oxidation and acid catalyzed paal knorr synthesis
Bulletin of The Korean Chemical Society, 2012Co-Authors: Se Hee Kim, Jin Woo Lim, Cheol Hee Lim, Jae Nyoung KimAbstract:E-mail: kimjn@chonnam.ac.krReceived December 6, 2011, Accepted December 19, 2011An efficient synthesis of poly-substituted furans, pyrroles, and thiophenes was carried out in a regiocontrolledmanner via a three-step process; (i) conjugate addition of Methyl Cyanoacetate derivatives to α,β-enones, (ii)CuI-mediated aerobic oxidation, and (iii) Paal-Knorr type synthesis of five-membered heterocycles. Key Words : Furans, Pyrroles, Thiophenes, CuI, Paal-Knorr synthesisIntroductionRecently, we reported an efficient synthesis of 2,5-diketo-esters via a conjugate addition of Methyl Cyanoacetate toα,β-unsaturated ketone and a following CuI-mediated aerobicoxidation.
-
construction of 1 2 5 tricarbonyl compounds using Methyl Cyanoacetate as a glyoxylate anion synthon combined with copper i iodide catalyzed aerobic oxidation
Advanced Synthesis & Catalysis, 2011Co-Authors: Se Hee Kim, Ko Hoon Kim, Jae Nyoung KimAbstract:A practical and efficient synthesis of various 1,2,5-tricarbonyl compounds is described. The synthesis has been carried out by a conjugate addition of Methyl Cyanoacetate to the β-position of α,β-unsaturated carbonyl compounds and a subsequent copper(I) iodide-catalyzed aerobic oxidation. In addition, various α-aryl- and α-alkyl-α-keto esters have been synthesized using a similar approach.
Igor Reva - One of the best experts on this subject based on the ideXlab platform.
-
Missing conformers. Comparative study of conformational cooling in cyanoacetic acid and Methyl Cyanoacetate isolated in low temperature inert gas matrixes
Chemical Physics Letters, 2003Co-Authors: Igor Reva, Stepan G. Stepanian, Ludwik Adamowicz, Rui FaustoAbstract:Abstract A comparative conformational study of two related systems, Methyl Cyanoacetate (MCA) and cyanoacetic acid (CAA), is presented. Ab initio calculations predicted that both systems have two nearly isoenergetic conformers separated by similar low energy barriers (about 3 kJ mol −1 ). In xenon matrixes deposited at temperatures above 40 K for MCA and above 20 K for CAA only one conformer was observed for each of the two systems. However, below those temperatures two MCA and two CAA conformers were trapped into the matrixes. Conformational cooling was found responsible for this behavior. Factors contributing to this effect are discussed.
-
Conformational isomerism in Methyl Cyanoacetate: A combined matrix-isolation infrared spectroscopy and molecular orbital study
Physical Chemistry Chemical Physics, 2001Co-Authors: Igor Reva, Sonia Ilieva, Rui FaustoAbstract:Study of the conformational isomerism of Methyl Cyanoacetate (NCCH2COOCH3, MCA) aided for the first time by matrix-isolation infrared spectroscopy is reported. The conformational isomerization processes in MCA in the temperature range from 10 to 70 K were studied in detail in argon and xenon matrixes. During annealing of the matrixes direct interconversion of the gauche into the syn conformer has been registered. A similar, but more pronounced, gauche → syn interconversion effect was observed in a series of experiments in which matrixes were deposited at increased substrate temperature. The experiment is supported by theoretical predictions undertaken at different levels of approximation (MP2 and DFT/B3LYP). It is shown that, for the single molecule in vacuum, the syn conformer (C–C–CO dihedral angle equal to 0°) corresponds to the conformational ground state, with the doubly degenerated by symmetry gauche conformer (C–C–CO dihedral angle equal to ± 139.9°) being only slightly less stable than the most stable form (MP2/6-31G** ΔE(gauche → syn) = 0.174 kJ mol−1). In the matrixes, the energy gap between the syn and gauche conformers increases, with ΔE(gauche → syn) estimated to be about 1.4 kJ mol−1 in xenon. The predicted energy barriers for conformer interconversion were found to be significantly low: the MP2/6-31G** calculated ΔE(syn → gauche) energy barrier is ca. 3.65 kJ mol−1, while the calculated energy barrier separating the two symmetrically equivalent gauche conformers stays only 0.196 kJ mol−1 above the energy of these forms. In the matrixes, ΔE(syn → gauche) energy barrier increases to at least 17–18 kJ mol−1, while the ΔE(gauche → gauche) energy barrier is, with all probability, still lower than in the gaseous phase. The matrix isolation spectroscopic data indicate that interconversion between the gauche conformers occurs even in the low temperature matrixes.
Paul Burrow - One of the best experts on this subject based on the ideXlab platform.
-
Electron attachment to dye-sensitized solar cell components: cyanoacetic acid.
The journal of physical chemistry. A, 2011Co-Authors: Alberto Modelli, Paul BurrowAbstract:The energies of electron attachment associated with temporary occupation of the lower-lying virtual orbitals of cyanoacetic acid (CAA), proposed as a possible component of dye-sensitized solar cells, and its derivative Methyl Cyanoacetate (MCA) are measured in the gas phase with electron transmission spectroscopy (ETS). The corresponding orbital energies of the neutral molecule, supplied by B3LYP/6-31G(d) calculations and scaled using an empirically calibrated linear equation, are compared with the experimental vertical attachment energies (VAEs). The vertical and adiabatic electron affinities are also evaluated at the B3LYP/6-31+G(d) level as the anion/neutral total energy difference. Dissociative electron attachment spectroscopy (DEAS) is used to measure the total anion current as a function of the incident electron energy in the 0-4 eV energy range, and the negative fragments generated through the dissociative decay channels of the molecular anion are detected with a mass filter. In both compounds only two intense fragment anion currents are observed, that due to loss of a hydrogen atom from the molecular anion ([M - H](-)) and that due to formation of CN(-). In CAA the former signal displays a very sharp feature at 0.68 eV, assigned to a vibrational Feshbach resonance arising from coupling between a dipole bound anion state and a temporary σ* anion state.
Se Hee Kim - One of the best experts on this subject based on the ideXlab platform.
-
construction of 1 2 5 tricarbonyl compounds using Methyl Cyanoacetate as a glyoxylate anion synthon combined with copper i iodide catalyzed aerobic oxidation
ChemInform, 2012Co-Authors: Se Hee Kim, Ko Hoon Kim, Jae Nyoung KimAbstract:A variety of α-cyano-δ-ketocarboxylates (I) and (III), obtained by conjugate addition of Cyanoacetate towards α,β-unsaturated ketones, is efficiently oxidized to the corresponding α,δ-diketo esters (II) and (IV), respectively.
-
facile regiocontrolled three step synthesis of poly substituted furans pyrroles and thiophenes consecutive michael addition of Methyl Cyanoacetate to α β enone cui mediated aerobic oxidation and acid catalyzed paal knorr synthesis
Bulletin of The Korean Chemical Society, 2012Co-Authors: Se Hee Kim, Jin Woo Lim, Cheol Hee Lim, Jae Nyoung KimAbstract:E-mail: kimjn@chonnam.ac.krReceived December 6, 2011, Accepted December 19, 2011An efficient synthesis of poly-substituted furans, pyrroles, and thiophenes was carried out in a regiocontrolledmanner via a three-step process; (i) conjugate addition of Methyl Cyanoacetate derivatives to α,β-enones, (ii)CuI-mediated aerobic oxidation, and (iii) Paal-Knorr type synthesis of five-membered heterocycles. Key Words : Furans, Pyrroles, Thiophenes, CuI, Paal-Knorr synthesisIntroductionRecently, we reported an efficient synthesis of 2,5-diketo-esters via a conjugate addition of Methyl Cyanoacetate toα,β-unsaturated ketone and a following CuI-mediated aerobicoxidation.
-
construction of 1 2 5 tricarbonyl compounds using Methyl Cyanoacetate as a glyoxylate anion synthon combined with copper i iodide catalyzed aerobic oxidation
Advanced Synthesis & Catalysis, 2011Co-Authors: Se Hee Kim, Ko Hoon Kim, Jae Nyoung KimAbstract:A practical and efficient synthesis of various 1,2,5-tricarbonyl compounds is described. The synthesis has been carried out by a conjugate addition of Methyl Cyanoacetate to the β-position of α,β-unsaturated carbonyl compounds and a subsequent copper(I) iodide-catalyzed aerobic oxidation. In addition, various α-aryl- and α-alkyl-α-keto esters have been synthesized using a similar approach.