المؤلفون: Alexander E. Pogonin, Ivan Yu. Kurochkin, Alexey V. Eroshin, Maksim N. Zavalishin, Yuriy A. Zhabanov

المصدر: Physchem, Vol 4, Iss 2, Pp 131-145 (2024)

مصطلحات موضوعية: gas-phase electron diffraction, molecular structure, quantum chemistry, azobenzene, pseudoconformer, Physical and theoretical chemistry, QD450-801

الوصف: The geometrical re parameters of trans-azobenzene (E-AB) free molecule were refined by gas electron diffraction (GED) method using available experimental data obtained previously by S. Konaka and coworkers. Structural analysis was carried out by various techniques. First of all, these included the widely used molecular orbital constrained gas electron diffraction method and regularization method. The results of the refinements using different models were also compared—a semirigid model, three variants of one-dimensional dynamic models, and a two-dimensional pseudoconformer model. Several descriptions have been used due to the fact that E-AB has a shallow potential energy surface along the rotation coordinates of phenyl groups. Despite this, it turned out that the semirigid model is suitable for use for E-AB and allows good agreement with experimental data to be achieved. According to the results of GED structural analysis, coupled with the results of DLPNO-CCSD(T0) calculations, E-AB has a planar structure. Based only on GED data, it is impossible to unambiguously determine the rotational angle of the phenyl group due to the facts that (i) with rotation over a wide range of angles, the bonded distances in the molecule change insignificantly and (ii) potential function in a structural analysis within a dynamic model is not determined with the necessary accuracy. This work also examines the sensitivity of the GED method to structural changes caused by trans-cis isomerization. The paper also analyzes the applicability of different variants of density functional theory (DFT) calculations in GED structural analysis using E-AB as an example. There are not enough similar methodological works in the literature. This experimental and methodological information is especially important and relevant for planning and implementing GED experiments and corresponding processing of the results for azobenzene derivatives, in which the conformer and isomeric diversity are even more complicated due to the presence of different substituents.

وصف الملف: electronic resource

العلاقة: https://www.mdpi.com/2673-7167/4/2/10Test; https://doaj.org/toc/2673-7167Test

الوصول الحر: https://doaj.org/article/5c40d4364f584554804a17400f34caf4Test

المؤلفون: Noble-Eddy, Robert

المساهمون: Masters, Sarah., Rankin, David

مصطلحات موضوعية: 543, gas-phase electron diffraction, GED, phosphines, flash vacuum pyrolysis, FVP

الوصف: Gas-phase electron diffraction (GED) is the only viable technique for the accurate structural study of gas-phase molecules that contain more than ~10 atoms. Recent advances in Edinburgh have made it possible to study larger, more complex, stable molecules using the SARACEN method. This thesis is concerned with obtaining the structures of unstable species, using both standard GED techniques and by developing a new method in which ash vacuum pyrolysis is used to generate short-lived species in situ. In the first part of this thesis nine primary phosphines (R-PH2) with different substituents (R = methyl, vinyl, ethynyl, allenyl, allyl, propargyl, phenyl, benzyl and chloromethyl) are studied by GED. Vinylarsine and vinyldichloroarsine are also studied. Primary phosphines and arsines appear infrequently in the literature owing to their toxicity and high reactivity, especially of the unsaturated systems. The conformational behaviour in these molecules and trends throughout the series are rationalised. As appropriate, comparisons are made to analogous amines and the differences found are discussed. Tertiary phosphines (R3P) are routinely protected by complexation with borane (BH3) and it has been proposed that this technique could be extended to primary phosphines. As an extension of the initial investigation, the GED study of methylphosphine-borane offers an insight into structural changes that occur upon complexation, although attempts to study larger phosphine-borane complexes by GED proved dificult. The structures and bonding trends in a series of phosphineborane adducts are discussed, mainly using the results of ab initio calculations. The second part of the thesis details the implementation of a new, very high temperature nozzle, which allows the generation of short-lived species by pyrolysis. The workings of this nozzle are discussed and the study of the structure of ketene, generated from three different precursors, is detailed. The benzyl radical has also been studied, and a preliminary GED structure is presented. As a result of this work the molecular structures of Meldrum's acid and dibenzylsulfone are also presented, having been determined in the gas phase for the first time.

الوصول الحر: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.562601Test

المؤلفون: Blake, Alexander J.

مصطلحات موضوعية: dynamic models, gas-phase electron diffraction, molecular flexibility, phase transitions, X-ray diffraction

الوصف: A historical challenge: Gas-phase electron diffraction and single-crystal X-ray diffraction are both established techniques, but they were both pushed to their limits by the challenge posed by the highly flexible tetranitromethane molecule. New approaches had to be developed for the structure of the molecule to be elucidated.

العلاقة: https://nottingham-repository.worktribe.com/output/883343Test; Angewandte Chemie International Edition; Volume 56; Issue 39; Pagination 11697-11698; https://nottingham-repository.worktribe.com/file/883343/1/SBlake%20Structure%20determination%20techniques%20flex.pdfTest

الإتاحة: https://doi.org/10.1002/anie.201706526Test
https://nottingham-repository.worktribe.com/file/883343/1/SBlake%20Structure%20determination%20techniques%20flex.pdfTest
https://nottingham-repository.worktribe.com/output/883343Test

المؤلفون: Lars Zimmermann, Norbert W. Mitzel, Timo Glodde, Beate Neumann, Hans-Georg Stammler, Yury V. Vishnevskiy

المصدر: Angewandte Chemie (International Ed. in English)

مصطلحات موضوعية: gas phase electron diffraction, Materials science, Ab initio, chemistry.chemical_element, 010402 general chemistry, 01 natural sciences, Catalysis, Chalcogen Bonding, Chalcogen, chemistry.chemical_compound, σ-holes, intermolecular interactions, 010405 organic chemistry, Communication, Intermolecular force, General Chemistry, Communications, 0104 chemical sciences, Crystallography, chemistry, Electron diffraction, Intramolecular force, Tellurium, Derivative (chemistry), Natural bond orbital

الوصف: (C6F5)Te(CH2)3NMe2 (1), a perfluorophenyltellurium derivative capable of forming intramolecular N⋅⋅⋅Te interactions, was prepared and characterized. The donor‐free reference substance (C6F5)TeMe (2) and the unsupported adduct (C6F5)(Me)Te⋅NMe2Et (2 b) were studied in parallel. Molecular structures of 1, 2 and 2 b were determined by single‐crystal X‐ray diffraction and for 1 and 2 by gas‐phase electron diffraction. The structure of 1 shows N⋅⋅⋅Te distances of 2.639(1) Å (solid) and 2.92(3) Å (gas). Ab initio plus NBO and QTAIM calculations show significant charge transfer effects within the N⋅⋅⋅Te interactions and indicate σ‐hole interactions.
Willing to interact are the tellurium and nitrogen atoms of Me2N(CH2)3Te(C6F5) as was experimentally proven both in the solid state and the gas phase.

وصف الملف: application/pdf

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::afdb67aa1015d0d7cd69ad2be593d5c3Test
https://doi.org/10.1002/anie.202013480Test

المؤلفون: De Almeida, Wagner B.

المصدر: Química Nova. October 2000 23(5)

مصطلحات موضوعية: cyclooctane, conformational analysis, ab initio calculations, gas phase electron diffraction

الوصف: The determination of the molecular structure of molecules is of fundamental importance in chemistry. X-rays and electron diffraction methods constitute in important tools for the elucidation of the molecular structure of systems in the solid state and gas phase, respectively. The use of quantum mechanical molecular orbital ab initio methods offer an alternative for conformational analysis studies. Comparison between theoretical results and those obtained experimentally in the gas phase can make a significant contribution for an unambiguous determination of the geometrical parameters. In this article the determination of the molecular structure of the cyclooctane molecule by electron diffraction in the gas phase and ab initio calculations will be addressed, providing an example of a comparative analysis of theoretical and experimental predictions.

وصف الملف: text/html

الوصول الحر: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422000000500006Test

المؤلفون: Wagner B. De Almeida

المصدر: Química Nova, Vol 23, Iss 5, Pp 600-607 (2000)

مصطلحات موضوعية: cyclooctane, conformational analysis, ab initio calculations, gas phase electron diffraction, Chemistry, QD1-999

الوصف: The determination of the molecular structure of molecules is of fundamental importance in chemistry. X-rays and electron diffraction methods constitute in important tools for the elucidation of the molecular structure of systems in the solid state and gas phase, respectively. The use of quantum mechanical molecular orbital ab initio methods offer an alternative for conformational analysis studies. Comparison between theoretical results and those obtained experimentally in the gas phase can make a significant contribution for an unambiguous determination of the geometrical parameters. In this article the determination of the molecular structure of the cyclooctane molecule by electron diffraction in the gas phase and ab initio calculations will be addressed, providing an example of a comparative analysis of theoretical and experimental predictions.

وصف الملف: electronic resource

العلاقة: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-40422000000500006Test; https://doaj.org/toc/0100-4042Test; https://doaj.org/toc/1678-7064Test

الوصول الحر: https://doaj.org/article/2fcc6426ceb74229b099797a425cab80Test

المؤلفون: Aarset, Kirsten, Page, Elizabeth M., Rice, David A.

مصطلحات موضوعية: Gas phase Electron diffraction, Ab initio, 2-hydroxybenzamide, 2- methoxybenzamide, VDP::Matematikk og Naturvitenskap: 400::Kjemi: 440::Fysikalsk kjemi: 443

الوصف: The structures of 2-hydroxybenzamide (C 7 H 7 NO 2 ) and 2-methoxybenzamide (C 8 H 9 NO 2) have been determined in the gas-phase by electron diffraction using results from quantum chemical calculations to inform restraints used on the structural parameters. Theoretical methods (HF and MP2/6-311+G(d,p)) predict four stable conformers for both 2- hydroxybenzamide and 2-methoxybenzamide. For both compounds evidence for intramolecular hydrogen bonding is presented. In 2- hydroxybenzamide the observed hydrogen bonded fragment is between the hydroxyl and carbonyl groups while in 2- methoxybenzamide the hydrogen bonded fragment is between one of the hydrogen atoms of the amide group and the methoxy oxygen atom. ; Postprint version of published article

وصف الملف: application/pdf

العلاقة: The Journal of Physical Chemistry A;117(14); Aarset, K., Page, E. M., & Rice, D. A. (2013). Hydrogen Bonding in the Gas-Phase: The Molecular Structures of 2-Hydroxybenzamide (C7H7NO2) and 2-Methoxybenzamide (C8H9NO2), Obtained by Gas-Phase Electron Diffraction and Theoretical Calculations. The Journal of Physical Chemistry A, 117(14), 3034-3040.; urn:issn:1089-5639; FRIDAID 965979; https://hdl.handle.net/10642/2039Test; http://dx.doi.org/10.1021/jp311003dTest

الإتاحة: https://doi.org/10.1021/jp311003dTest
https://hdl.handle.net/10642/2039Test

المؤلفون: Natalya V. Belova, Georgiy V. Girichev, Vitaliya E. Kotova, Oleg A. Pimenov

المصدر: Journal of Molecular Structure

مصطلحات موضوعية: Pyridine-N-oxides, Substituent, Electron density distribution, 010402 general chemistry, Mass spectrometry, 01 natural sciences, Article, Analytical Chemistry, Inorganic Chemistry, chemistry.chemical_compound, Substituent effect, Atomic orbital, Pyridine, Molecule, Quantum chemical calculations, Spectroscopy, 010405 organic chemistry, Chemistry, Organic Chemistry, Gas-phase electron diffraction, 0104 chemical sciences, Bond length, Crystallography, Electron diffraction, Molecular structure, Natural bond orbital

الوصف: The molecular structure of 4-nitropyridine N-oxide, 4-NO2-PyO, has been determined by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and by quantum chemical calculations (DFT and MP2). Comparison of these results with those for non-substituted pyridine N-oxide and 4-methylpyridine N-oxide CH3-PyO, demonstrate strong substitution effects on structural parameters and electron density distribution. The presence of the electron-withdrawing –NO2 group in para-position of 4-NO2-PyO results in an increase of the ipso-angle and a decrease of the semipolar bond length r(N→O) in comparison to the non-substituted PyO. The presence of the electron-donating –CH3 group in 4-CH3-PyO leads to opposite structural changes. Electron density distribution in pyridine-N-oxide and its two substituted compounds are discussed in terms of natural bond orbitals (NBO) and quantum theory atoms in molecule (QTAIM).
Graphical abstract Image 1
Highlights • The molecular structure of 4-nitropiridine-N-oxide, 4-NO2-PyO, has been studied by GED/MS and quantum chemical calculations. • The molecule possesses C 2v molecular symmetry with the planar pyridine ring. • Obtained molecular parameters for PyO, 4-NO2-PyO, and 4-MePyO confirm the p-conjugation in the pyridine ring. • The presence of electron withdrawing -NO2 group results in a shortening of r(N→O) and decreasing the oxygen negative net charge. • N→O semipolar bond is predominantly covalent and possess the cylindrical symmetry.

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::99b7e109025cfe8acd7744890fed1fa1Test
https://pubmed.ncbi.nlm.nih.gov/32427177Test

المؤلفون: Natalya V. Belova, Georgiy V. Girichev, Nguyen Hoang Trang, Vitaliya E. Kotova, Kseniya A. Korolkova

المصدر: Journal of Molecular Structure

مصطلحات موضوعية: 0301 basic medicine, Electron density, Gas electron diffraction, 030106 microbiology, Nuclear magnetic resonance crystallography, 010402 general chemistry, Hyperconjugation, 01 natural sciences, Quantum chemistry, Article, Analytical Chemistry, 4-methylpyridine-N-oxide, Inorganic Chemistry, 03 medical and health sciences, Computational chemistry, Molecular symmetry, Molecule, Quantum chemical calculations, NBO analysis, Physics::Chemical Physics, Spectroscopy, Chemistry, Organic Chemistry, Gas-phase electron diffraction, 0104 chemical sciences, Physical chemistry, Molecular structure, Natural bond orbital

الوصف: The molecular structure of 4-methylpiridine-N-oxide, 4-MePyO, has been studied by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both, quantum chemistry and GED analyses resulted in CS molecular symmetry with the planar pyridine ring. Obtained molecular parameters confirm the hyperconjugation in the pyridine ring and the sp2 hybridization concept of the nitrogen and carbon atoms in the ring. The experimental geometric parameters are in a good agreement with the parameters for non-substituted N-oxide and reproduced very closely by DFT calculations. The presence of the electron-donating CH3 substituent in 4-MePyO leads to a decrease of the ipso-angle and to an increase of r(N→O) in comparison with the non-substituted PyO. Electron density distribution analysis has been performed in terms of natural bond orbitals (NBO) scheme. The nature of the semipolar N→O bond is discussed.
Graphical abstract Image 1
Highlights • The molecular structure of 4-methylpiridine-N-oxide has been studied by GED and quantum chemical calculations. • Electron density distribution analysis has been performed in terms of natural bond orbitals (NBO) scheme. • The molecule possesses C S symmetry with the planar pyridine ring. • Obtained molecular parameters confirm the hyperconjugation in the pyridine ring. • The presence of the electron-donating CH3 substituent in 4-MePyO results in an increase of r(N→O).

الوصول الحر: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::6bb89b619bf6abbd67758953b70aeffeTest
https://doi.org/10.1016/j.molstruc.2017.11.070Test

المؤلفون: Aarset, Kirsten, Page, Elizabeth M., Rice, David A.

مصطلحات موضوعية: GED, Gas-phase electron diffraction, Hexamethyldigermane, VDP::Medisinske Fag: 700::Basale medisinske, odontologiske og veterinærmedisinske fag: 710::Medisinsk molekylærbiologi: 711, odontologiske og veterinærmedisinske fag: 710::Medisinsk biokjemi: 726

الوصف: Gas-phase electron diffraction (GED) data together with results from ab initio molecular orbital calculations (HF and MP2/6-311+G(d,p)) have been used to determine the structure of hexamethyldigermane ((CH3)3Ge−Ge(CH3)3). The equilibrium symmetry is D3d, but the molecule has a very low-frequency, large-amplitude, torsional mode (CGeGeC) that lowers the thermal average symmetry. The effect of this large-amplitude mode on the interatomic distances was described by a dynamic model which consisted of a set of pseudoconformers spaced at even intervals. The amount of each pseudoconformer was obtained from the ab initio calculations (HF/6-311+G(d,p)). The results for the principal distances (ra) and angles (h1) obtained from the combined GED/ab initio (with estimated 1σ uncertainties) are r(Ge−Ge) = 2.417(2) Å, r(Ge−C) = 1.956(1) Å, r(C−H) = 1.097(5) Å, GeGeC = 110.5(2)°, and GeCH = 108.8(6)°. Theoretical calculations were performed for the related molecules ((CH3)3Si−Si(CH3)3 and (CH3)3C−C(CH3)3).

وصف الملف: application/pdf

العلاقة: Journal of Physical Chemistry A;114 (26); Aarset, K., Page, E.M. & Rice, D.A. (2010). The Molecular Structure of Hexamethyldigermane Determined by Gas-Phase Electron Diffraction with Theoretical Calculations for (CH3)(3)M-M(CH3)(3) Where M = C, Si, and Ge. Journal of Physical Chemistry A, 114 (26), 7187-7190; urn:issn:1089-5639; FRIDAID 367938; http://dx.doi.org/10.1021/jp1026042Test; https://hdl.handle.net/10642/641Test

الإتاحة: https://doi.org/10.1021/jp1026042Test
https://hdl.handle.net/10642/641Test