Ketene Structure Research Articles

Exploring the metallurgical coke thermal properties in viewpoint of experiment and molecular simulation

The Chinese standard method of GB/T 4000–2017 was unable to accurately measure the coke thermal properties in the large blast furnace. Therefore, the coke compressive strength (CCS) test at a high temperature was designed to examine the coke thermal properties. Then, the large-scale coke model (sp2C17421sp3C6579) was established. After, the ReaxFF molecular dynamics simulations were implemented to mimic the coke solution loss (CSL) and the CCS at the high temperature. It was found that the adsorption energy and the diffusion energy of micropores were greater than those of mesopores and macropores, indicating that the CSL reaction mainly happened in the coke micropore. It was discovered that the CSL reaction mechanism was the sp3 C oxidization mechanism with the transient state of ketene structure. And, it was detected that the CCS process was divided into the plastic deformation, the instantaneous fracture and the elastic deformation and yield, which was caused by the local reconstruction, the overall folding and the center stretching of carbon layer, respectively. By comparing simulated results with experiments, it was proved that obtained mechanisms were valid. The proposed experimental and simulated methods provided a novel method to measure and understand the coke thermal properties.

Improved semi-experimental equilibrium structure and high-level theoretical structures of ketene.

The millimeter-wave rotational spectrum of ketene (H2C=C=O) has been collected and analyzed from 130 to 750GHz, providing highly precise spectroscopic constants from a sextic, S-reduced Hamiltonian in the Ir representation. The chemical synthesis of deuteriated samples allowed spectroscopic measurements of five previously unstudied ketene isotopologues. Combined with previous work, these data provide a new, highly precise, and accurate semi-experimental (reSE) structure for ketene from 32 independent moments of inertia. This reSE structure was determined with the experimental rotational constants of each available isotopologue, together with computed vibration-rotation interaction and electron-mass distribution corrections from coupled-cluster calculations with single, double, and perturbative triple excitations [CCSD(T)/cc-pCVTZ]. The 2σ uncertainties of the reSE parameters are ≤0.0007 Å and 0.014° for the bond distances and angle, respectively. Only S-reduced spectroscopic constants were used in the structure determination due to a breakdown in the A-reduction of the Hamiltonian for the highly prolate ketene species. All four reSE structural parameters agree with the "best theoretical estimate" (BTE) values, which are derived from a high-level computed re structure [CCSD(T)/cc-pCV6Z] with corrections for the use of a finite basis set, the incomplete treatment of electron correlation, relativistic effects, and the diagonal Born-Oppenheimer breakdown. In each case, the computed value of the geometric parameter lies within the statistical experimental uncertainty (2σ) of the corresponding semi-experimental coordinate. The discrepancies between the BTE structure and the reSE structure are 0.0003, 0.0000, and 0.0004 Å for rC-C, rC-H, and rC-O, respectively, and 0.009° for θC-C-H.

Gas-Phase Structures of Ketene and Acetic Acid from Acetic Anhydride Using Very-High-Temperature Gas Electron Diffraction.

The gas-phase molecular structure of ketene has been determined using samples generated by the pyrolysis of acetic anhydride (giving acetic acid and ketene), using one permutation of the very-high-temperature (VHT) inlet nozzle system designed and constructed for the gas electron diffraction (GED) apparatus based at the University of Canterbury. The gas-phase structures of acetic anhydride, acetic acid, and ketene are presented and compared to previous electron diffraction and microwave spectroscopy data to show improvements in data extraction and manipulation with current methods. Acetic anhydride was modeled with two conformers, rather than a complex dynamic model as in the previous study, to allow for inclusion of multiple pyrolysis products. The redetermined gas-phase structure of acetic anhydride (obtained using the structure analysis restrained by ab initio calculations for electron diffraction method) was compared to that from the original study, providing an improvement on the description of the low vibrational torsions compared to the dynamic model. Parameters for ketene and acetic acid (both generated by the pyrolysis of acetic anhydride) were also refined with higher accuracy than previously reported in GED studies, with structural parameter comparisons being made to prior experimental and theoretical studies.

ChemInform Abstract: Catalytic Asymmetric Ketene [2+2] and [4+2] Cycloadditions

AbstractReview: 242 refs.

Direct Observation of Metal Ketenes Formed by Photoexcitation of a Fischer Carbene using Ultrafast Infrared Spectroscopy

Fischer carbenes are commonly used as reagents in the synthesis of new carbon–carbon bonds, a reaction made possible by the unique chemistry of the formal metal–carbon double bond. Nevertheless, the photoinduced reactions of these complexes are relatively poorly understood. For instance, it has been postulated but not confirmed that visible irradiation leads to photocarbonylation, in which a CO ligand inserts into the metal–carbon bond to form a metal ketene intermediate. Here, we report the first direct observation of this intermediate following 400 nm photoexcitation of the model group 6 Fischer carbene Cr(CO)5[CCH3(OCH3)]. Using ultrafast time-resolved infrared spectroscopy (TRIR), we observe the formation of three distinct metal ketene structures, which we assign as a singlet and two isoenergetic triplet excited-state structures. The singlet relaxes to the ground state on a time scale of ∼35 ps, whereas the two triplets are long-lived (>2 ns). TRIR of the tungsten analogue yields no evidence for a metal ketene structure, consistent with the limited reactivity of this complex. The results directly elucidate the fundamental role of triplet metal ketenes in the photoreactivity of Fischer carbene complexes.

When Does Carbonylation of Carbenes Yield Ketenes? A Theoretical Study with Implications for Synthesis

Quantum-chemical calculations using DFT and ab initio methods have been carried out for 32 carbenes RR'C which comprise different classes of compounds and the associated ketenes RR'C═C═O. The calculated singlet-triplet gaps ΔE(S-T) of the carbenes exhibit a very high correlation with the bond dissociation energies (BDEs) of the ketenes. An energy decomposition analysis of the RR'C-CO bond using the triplet states of the carbene and CO as interacting fragments supports the assignment of ΔE(S-T) as the dominant factor for the BDE but also shows that the specific interactions of the carbene may sometimes compensate for the S/T gap. The trend of the interaction energy ΔE(int) values is mainly determined by the Pauli repulsion between the carbene and CO. The stability of amino-substituted ketenes strongly depends on the destabilizing conjugation between the nitrogen lone-pair orbital and the ketene double bonds. There is a ketene structure of the unsaturated N-heterocyclic carbene parent compound NHC1 with CO as a local energy minimum on the potential-energy surface. However, the compound NHC1-CO is thermodynamically unstable toward dissociation. The saturated homologue NHC2-CO has only a very small bond dissociation energy of D(e) = 3.2 kcal/mol. The [3]ferrocenophane-type compound FeNHC-CO has a BDE of D(e) = 16.0 kcal/mol.

Mecanisme De Decarbonylation De Pyrazolides Ionises Par Impact Electronique

Electron impact ionization of 1-acryloylpyrazole [1] induces a unimolecular loss of CO forming ionized 1-vinylpyrazole [2] as shown by metastable ion characteristics and neutralization-reionization data. This CO loss implies a rate-determining isomerization process into a pyrazolylmethyl ketene structure 1a+. These ketene ions have been synthetized in the ion source by dissociative ionization of pyrazolylpropionylpyrazoles. Flash-vacuum pyrolysis of these compounds also affords the expected neutral ketenes in the gas phase, which are however readily converted into the acryloyl isomers by an intramolecular nucleophilic process.

ChemInform Abstract: Synthesis and Reactivities of Novel η2-(C,O) Alkylphenylketene Complexes of Nickel. Coordination-Mode Switching Reaction of the Ketene Ligand.

Abstract A series of bis(tertiary phosphine)(alkylphenylketene)nickel complexes, Ni[(C 6 H 5 (R)CCO)L 2 [R  CH 3 ( a ), C 2 H 5 ( b ); L  P(C 6 H 5 ) 3 ( 1 ), P(C 6 H 5 ) 2 ( p -CH 3 C 6 H 4 ) ( 2 )], were isolated from the reaction of bis(1,5-cyclooctadiene)nickel with alkylphenylketene in the presence of the corresponding tertiary phosphines. The spectroscopic analyses of 1 and 2 suggest η 2 -(C,O) to be a ketene structure close to the structure of oxanickelacyclopropane. Based on their chemical reactivities and fluxional behaviors in 1 H and 13 C NMR, the ketene moieties of 1 and 2 switch their coordination-mode from η 2 -(C,O) to η 2 -(C,C) type via an associative process involving binuclear μ-ketene intermediates prior to undergoing further reactions.

Infrared spectra and quantum chemical characterization of weakly bound clusters of the benzoyl cation with Ar and H2O

Weakly-bound clusters of the closed-shell benzoyl cation (C(6)H(5)CO(+), PhCO(+)) with Ar and H(2)O are investigated by infrared (IR) spectroscopy, mass spectrometry, and quantum chemical calculations in order to characterize the interaction of a closed shell aromatic cation with a nonpolar and a polar ligand. PhCO(+)-L dimers are produced by electron ionization of benzaldehyde in a supersonic plasma expansion. IR photodissociation (IRPD) spectra of PhCO(+)-L with L = Ar and H(2)O are analyzed in the C-O, C-H, and O-H stretch ranges (2000-3900 cm(-1)). The potential energy surface of the PhCO(+)-L dimers is characterized at the MP2/6-311++G(2df,2pd) level to locate the various minima and determine their energetic and vibrational properties. PhCO(+)-Ar prefers intermolecular π-bonding to the aromatic ring with a bond energy of D(0) = 6 kJ mol(-1). The weak interaction implies that the IRPD spectrum of PhCO(+)-Ar is very close to the IR spectrum of bare PhCO(+). The detection of the C-H and C-O stretch fundamentals provides valuable information about the C-O and C-H bond strengths in this prototypical aromatic acylium ion. Moreover, a variety of weak combination and overtone bands are assigned. The global minimum on the PhCO(+)-H(2)O potential has a planar charge-dipole configuration with D(0) = 41 kJ mol(-1) (with only the two H(2)O protons being out-of-plane), in which the lone pairs of H(2)O interact with the positive partial charges on the carbonyl carbon atom and the proton of the CH group in ortho position. The experimental IRPD spectra are in accord with the calculated global minima. The analysis of the charge distribution shows that the PhCO(+) cation is best represented as an oxocarbenium ion (Ph-C(+)[double bond, length as m-dash]O) with smaller contributions of the ketene structure (Ph(+)[double bond, length as m-dash]C[double bond, length as m-dash]O). This view is supported by the geometrical and vibrational properties of PhCO(+) as well as the shape of the intermolecular PhCO(+)-L dimer potentials.

Structure of ketene – Revisited re (equilibrium) and rm (mass-dependent) structures

The structure of ketene has been revisited on the basis of five new investigated isotopologues which, added to the existing six, rise their number to eleven. This gives an useful basis for new discussions about the structure. The quadratic, cubic and semi-diagonal quartic force field of ketene has been calculated at the MP2 level of theory employing a basis set of triple- ζ quality. A semi-experimental equilibrium structure has been derived from experimental ground state rotational constants and rovibrational interaction parameters calculated from the ab initio force field. This structure is in excellent agreement with the ab initio structure calculated at the CCSD(T) level of theory using a basis set of quintuple- ζ quality and a core correlation correction. The empirical structures including the mass-dependent r m structures have also been determined and their accuracy is discussed. The r m ( 1 r L ) method is the most stable under several testing conditions. However, the results are still not fully satisfactory. This is mainly due to the small coordinate of the keto-carbon.

The ketene intermediate in the photochemistry of ortho-nitrobenzaldehyde

The first intermediate of the photochemical transformation of ortho-nitrobenzaldehyde to ortho-nitrosobenzoic acid in acetonitrile solvent has been characterized by femtosecond spectroscopy and time-dependent density functional theory (TDDFT) calculations. Femtosecond stimulated Raman spectroscopy (FSRS) indicates that this intermediate adopts a ketene structure. This assignment is supported by the TDDFT results. A kinetic analysis of FSRS and transient absorption data points to two channels for the formation of the ketene. For the predominating first channel the formation takes 0.4 ps. For the second channel it is much slower and takes 220 ps. We assign the first channel to a reaction via an excited singlet state. The second one might involve a triplet state.

Bent Cyclopenta-2,4-dienylideneketene: Spectroscopic and ab initio Study of Reactive Intermediate

Results of an experimental and theoretical study of cyclopenta-2,4-dienylideneketene (3), a highly unstable reactive intermediate, are reported. The ketene was prepared, under matrix isolation conditions at 4.2 or 10 K, by laser photocarbonylation of 1,2-didehydrobenzene (1) photogenerated earlier from phthalic anhydride (2). FTIR polarization measurements performed on partially photooriented samples of 3 immobilized in solid neon or argon provide infrared transition moment directions for most of the observed vibrations. Experimental results confirm that the ketene is bent, as predicted by ab initio calculations. Utilizing two isotopically modified 3, 3b and 3c, on the basis of the infrared absorption spectrum alone, we have analyzed and assigned its vibrations in a way, which leaves no doubt about the bent ketene structure. This work was motivated by a long standing confusion surrounding the assignments of the vibrations in 1,2-didehydrobenzene (1), especially of its "triple" bond stretch.

The anharmonic force field and equilibrium molecular structure of ketene

A comprehensive anharmonic vibrational analysis of isotopic ketenes has been performed on the basis of a complete ab initio quartic force field constructed by means of second-order Mo/ller–Plesset perturbation theory (MP2) and the coupled-cluster singles and doubles (CCSD) approach, augmented for structural optimizations by a contribution for connected triple excitations [CCSD(T)]. The atomic-orbital basis sets of the study entailed C,O(10s6p/5s4p) and H(6s/4s) spaces multiply polarized in the valence region to give QZ(2d,2p) and QZ(2d1f,2p1d) sets. An iterative anharmonic vibrational refinement of a limited set of quadratic scaling parameters on 27 fundamentals of H2CCO, HDCCO, D2CCO, and H2C13CO generates a final quartic force field which reproduces the empirical νi data with an average absolute error of only 1.1 cm−1. This force field yields a complete and self-consistent set of Coriolis (ζij), vibrational anharmonic (χij), vibration–rotation interaction (αi), and quartic and sextic centrifugal distortion constants, providing a critical assessment of the assorted spectroscopic constants determined over many years and also facilitating future computations of vibrational state densities for detailed tests of unimolecular dissociation theories. The harmonic frequencies ascertained for H2CCO (in cm−1), with associated anharmonicities in parentheses, are ω1(a1)=3202.2(−129.2), ω2(a1)=2197.2(−44.4), ω3(a1)=1415.2(−25.9), ω4(a1)=1146.0(−29.7), ω5(b1)=581.9(+7.1), ω6(b1)=502.6(+26.3), ω7(b2)=3308.2(−141.3), ω8(b2)=996.0(−17.9), and ω9(b2)=433.6(+5.0). The large positive anharmonicity for the ν6(b1) C=C=O bending mode, which is principally a Coriolis effect, warrants continued investigation. Explicit first-order treatments of the strong Fermi interactions within the (ν4,2ν5,ν5+ν6,2ν6) manifold reveal resonance shifts for ν4(H2CCO, HDCCO, D2CCO) of (−12.1, −10.0, +12.2) cm−1, in order. The experimental assignments for this Fermi tetrad are confirmed to be problematic. From high-precision empirical rotational constants of six isotopomers and the theoretical anharmonic force field, the equilibrium structure of ketene is derived: re(C=O)=1.160 30(29) Å, re(C=C)=1.312 12(30) Å, re(C–H)=1.075 76(7) Å, and θe(H–C–H)=121.781(12)°. A natural bond orbital (NBO) analysis shows that the unusually large methylene angle is attributable to extensive in-plane π delocalization.

Silylated bisketenes: Accessible and reactive organic intermediates

Abstract

Synthesis and reactivities of novel η 2-(C,O) alkylphenylketene complexes of nickel. Coordination-mode switching reaction of the ketene ligand

A series of bis(tertiary phosphine)(alkylphenylketene)nickel complexes, Ni[(C 6H 5(R)CCO)L 2 [R  CH 3 ( a), C 2H 5 ( b); L  P(C 6H 5) 3 ( 1), P(C 6H 5) 2( p-CH 3C 6H 4) ( 2)], were isolated from the reaction of bis(1,5-cyclooctadiene)nickel with alkylphenylketene in the presence of the corresponding tertiary phosphines. The spectroscopic analyses of 1 and 2 suggest η 2-(C,O) to be a ketene structure close to the structure of oxanickelacyclopropane. Based on their chemical reactivities and fluxional behaviors in 1H and 13C NMR, the ketene moieties of 1 and 2 switch their coordination-mode from η 2-(C,O) to η 2-(C,C) type via an associative process involving binuclear μ-ketene intermediates prior to undergoing further reactions.

Substituent effects on ketene structure and stability: an ab initio study

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSubstituent effects on ketene structure and stability: an ab initio studyLeyi Gong, Michael A. McAllister, and Thomas T. TidwellCite this: J. Am. Chem. Soc. 1991, 113, 16, 6021–6028Publication Date (Print):July 1, 1991Publication History Published online1 May 2002Published inissue 1 July 1991https://doi.org/10.1021/ja00016a014RIGHTS & PERMISSIONSArticle Views718Altmetric-Citations96LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (957 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

ChemInform Abstract: Microwave Spectrum of Ketene

Abstract A new Stark-modulated submillimeter-wave spectrometer is described. This spectrometer has been used to analyze the microwave spectrum of three isotopomers (heavy atoms) of ketene. The rotational constants determined have been used to calculate the structure of ketene using a variety of methods. The question of planarity of ketene is also addressed. High-resolution microwave measurements have been used to determine the spin-rotation interaction in CH 2 13 CO.

Microwave spectrum of ketene

A new Stark-modulated submillimeter-wave spectrometer is described. This spectrometer has been used to analyze the microwave spectrum of three isotopomers (heavy atoms) of ketene. The rotational constants determined have been used to calculate the structure of ketene using a variety of methods. The question of planarity of ketene is also addressed. High-resolution microwave measurements have been used to determine the spin-rotation interaction in CH 2 13CO.

Synthesis and Reactivities of Novel η2-(C,O) Methylphenylketene Complex of Nickel

Abstract Bis(triphenylphosphine)(methylphenylketene)nickel complex (1) was cleanly isolated from the reaction of bis(1,5-cyclooctadiene)nickel with methylphenylketene in the presence of triphenylphosphine. The spectroscopic analyses of 1 suggest to be η2-(C,O) ketene structure being close to oxanickelacyclopropane structure. Based on the chemical reactivities of 1, it is proposed that the ketene moiety of 1 switches its coordination mode from η2-(C,O) to η2-(C,C) type prior to undergoing further reactions.

ChemInform Abstract: The Ground State Average Structure of Ketene.

Abstract The recently determined empirical/ab initio general harmonic force field of ketene is used to correct existing ground state rotational constants over five isotopic species of ketene to their zero-point average values. The latter determine structure parameters of high precision for this fundamentally important molecule. A marked asymmetrical change in the zero-point CH 2 group structure on partial deuteration is both predicted and found, such that the CH bond shortens and the CD bond lengthens, an effect contributed to by the significant amplitude of the very low frequency bending coordinates On complete deuteration, a small but “normal” zero-point CH bond shortening is determined and predicted. Equilibrium structure parameters are estimated to be r e (CH) = 1.0753(17) A, r e (CC) = 1.3142(5) A, r e (CO) = 1.1609(4) A, ∠ e (HCH) = 121.76(33)°.