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3-Center-4-Electron Bonding in [(silox)2Mo=NtBu]2(μ-Hg) Controls Reactivity while Frontier Orbitals Permit a Dimolybdenum π-Bond Energy Estimate
This article discusses 3-center-4-electron bonding. Abstract: Na/Hg reduction of (silox)2Cl2Mo=NtBu (3) afforded C2h [(silox)2Mo=NtBu]2(μ-Hg) (12-Hg), which consists of two distorted trigonal monoprisms with Hg at the each apex (d(MoHg) = 2.6810(5)Å). Calculations reveal 3c4e bonding in the linear MoHgMo linkage that renders 12-Hg susceptible to nucleophilic cleavage. Exposure to PMe3 and pyridine rapidly (<5 min) affords (silox)2(tBuN)MoLn (L = PMe3, n = 1 (1-PMe3); py, n = 2 (1-py2)), while poorer nucleophiles (L = C2H4, 2-butyne) yield adducts (e.g., 1-C2H4 and 1-C2Me2) after prolonged heating. The HOMO and LUMO of 12-Hg are "stretched" π and π* orbitals from which four states arise: 1Ag (GS), 3Bu, 1Bu, and 1Ag. ∆E = E(1Bu) - E(3Bu) = 2K, where K is the exchange energy. Magnetic studies indicate E(3Bu) - E(1Ag) ≈ 550 cm-1 (calcd 1744 cm-1), and a UV-vis absorption at 10 000 cm-1 is assigned to 1Ag → 1Bu, permitting K to be evaluated as 4725 cm-1. With the π → π* transition in Schrock's [Mo(NAr)(CH2tBu)(OC6F5)]2 (4) assigned at 528 nm, this estimation places its π-bond energy as {E(π2 → π-1 → π*1 in 4) - E(1Ag → 1Bu in 12-Hg)} + E(1Ag → 3Bu in 12-Hg) = 27 kcal/mol. digital.library.unt.edu/ark:/67531/metadc77136/
The 2011 Beta Eta Spring Banquet. Celebration of Rediscovery of the Elements
Article describing an Eta Beta celebration of the completion of James and Virginia Marshall's "Rediscovery of the Elements." Photographs from the event are included. Three separate articles appear on the right side of the page. digital.library.unt.edu/ark:/67531/metadc111260/
Abraham model correlations for solute partitioning into o-xylene, m-xylene and p-xylene from both water and the gas phase
This article discusses Abraham model correlations for solute partitioning into o-xylene, m-xylene and p-xylene from both water and the gas phase. Abstract: Experimental data have been compiled from the publisher literature on the partition coefficients of solutes and vapors into o-xylene, m-xylene and p-xylene at 298 K. The logarithms of the water-to-xylene partition coefficients, log P, and gas-to-xylene partition coefficients, log K, were correlated with the Abraham solvation parameter model. The derived mathematical expressions described the observed log P and log K data for the three xylene isomers to within average deviations of 0.14 log units or less. digital.library.unt.edu/ark:/67531/metadc155635/
Abraham Model Correlations for Transfer of Neutral Molecules and Ions to Sulfolane
This article discusses Abraham model correlations for the transfer of neutral molecules and ions to sulfolane. Data have been compiled from the published literature on the partition coefficients of solutes and vapors into anhydrous sulfolane. The logarithms of the water-to-sulfolane partition coefficients, log P, and gas-to-sulfolane partition coefficients, log K, were correlated with the Abraham solvation parameter model. The derived correlations described the observed log P and log K values for solutes dissolved in sulfolane to within average standard deviations of 0.14 log units or less. The log P correlation was extended to include the partition of ions by inclusion of a cation-solvent and an anion-solvent term. digital.library.unt.edu/ark:/67531/metadc157293/
Accurate Enthalpies of Formation of Alkali and Alkaline Earth Metal Oxides and Hydroxides: Assessment of the Correlation Consistent Composite Approach (ccCA)
This article discusses accurate enthalpies of formation of alkali and alkaline earth metal oxides and hydroxides. Abstract: Computing the enthalpies of formation for alkali metal and alkaline earth metal oxides (MₓO) and hydroxides [M(OH)n] using the Gaussian-n (Gn) and Weismann-n (Wn) ab initio model chemistries is difficult due to an improper treatment of core-valence electron correlation effects. Using a new model chemistry called the correlation consistent Composite Approach (ccCA), enthalpies of formation were determined for eight different alkali/alkaline earth metal oxides and hydroxides. Unlike the Gn and Wn model chemistries, which must be modified to properly account for core-valence electron correlation, the standard implementations of the ccCA provide acceptable results, and all enthalpies of formation obtained with the ccCA are within the accepted range of recommended values. digital.library.unt.edu/ark:/67531/metadc77173/
Activation of Carbon-Hydrogen and Hydrogen-Hydrogen Bonds by Copper-Nitrenes: A Comparison of Density Functionality Theory with Single- and Multireference Correlation Consistent Composite Approaches
This article discusses a comparison of density functional theory with single- and multireference correlation consistent composite approaches. Abstract: The kinetics and thermodynamics of copper-mediated nitrene insertion into C-H and H-H bonds (the former of methane) have been studied using several levels of theory: B3LYP/6-311++G(d,p), B97-1/cc-pVTZ, PBE1KCIS/cc-pVTZ, and ccCA (correlation consistent Composite Approach). The results show no significant difference among the DFT methods. All three DFT methods predict the ground state of the copper-nitrene model complex, L'Cu(NH), to be a triplet, while single reference ccCA predicts the singlet to be the ground state. The contributions to the total ccCA energy indicate that the singlet state is favored at the MP2/CBS level of theory, while electron correlation beyond this level (CCSD(T)) favors a triplet state, resulting in a close energetic balance between the two states. A multireference ccCA method is applied to the nitrene active species and supports the assignment of a singlet ground state. In general, the largest difference in the model reaction cycles between DFT and ccCA methods is for processes involving radicals and bond dissociation. digital.library.unt.edu/ark:/67531/metadc107767/
Activation of Carbon-Hydrogen Bonds via 1,2-Addition across M-X (X = OH or NH2) Bonds of d6 Transition Metals as a Potential Key Step in Hydrocarbon Functionalization: A Computational Study
This article discusses the activation of carbon-hydrogen bonds. Abstract: Recent reports of 1,2-addition of C-H bonds across Ru-X(X = amido, hydroxo) bonds of TpRu-(PMe₃)X fragments {Tp = hydridotris(pyrazolyl)borate} suggest opportunities for the development of new catalytic cycles for hydrocarbon functionalization. In order to enhance understanding of these transformations, computational examinations of the efficacy of model d6 transition metal complexes of the form [(Tab)M-(PH3)2X]q (Tab = tris-azo-borate; X = OH, NH2; q = -1 to +2; M = Tc(I), Re(I), Ru(II), Co(III), Ir(III), Ni(IV) Pt(IV) for the activation of benzene C-H bonds, as well as the potential for their incorporation into catalytic functionalization cycles, are presented. For the benzene C-H activation reaction steps, kite-shaped transition states were located and found to have relatively little metal-hydrogen interaction. The C-H activation process is best described as a metal-mediated proton transfer in which the metal center and ligand X function as an activating electrophile and intramolecular base, respectively. While the metal plays a primary role in controlling the kinetics and thermodynamics of the reaction coordinate for C-H activation/functionalization, the ligand X also influences the energetics. On the basis of three thermodynamic criteria characterizing salient energetic aspects of the proposed catalytic cycle and the detailed computational studies reported herein, late transition metal complexes (e.g., Pt, Co, etc.) in the d6 electron configuration {especially the TabCo(PH3)2(OH)+ complex and related Co(III) systems} are predicted to be the most promising for further catalyst investigation. digital.library.unt.edu/ark:/67531/metadc77141/
Activation of water on the TiO2 (110) surface: The case of Ti adatoms
This article discusses the activation of water on the TiO2 (110) surface. Abstract: Using first-principles calculations the authors have studied the reactions of water over Ti adatoms on the (110) surface of rutile TiO2. The authors' results provide fundamental insights into the microscopic mechanisms that drive this reaction at the atomic level and assess the possibility of using this system to activate the water dissociation reaction. In particular, the authors show that a single water molecule dissociates exothermically with a small energy barrier of 0.17 eV. After dissociation, both H⁺ and OH⁻ ions bind strongly to the Ti adatom, which serves as an effective reactive center on the TiO2 surface. Finally, clustering of Ti adatoms does not improve the redox activity of the system and results in a slightly higher energy barrier for water dissociation. digital.library.unt.edu/ark:/67531/metadc132989/
Application of the Correlation Consistent Composite Approach (ccCA) to Third-Row (Ga-Kr) Molecules
This article discusses the application of the correlation consistent composite approach (ccCA). Abstract: The correlation consistent composite approach (ccCA) has been applied to the G3/05 training set of 51 energetic properties for the atoms and molecules that contain the 4p elements, Ga-Kr. When atomic and molecular first-order spin orbit coupling corrections are added to open shell atoms and molecules, the ccCA has a mean absolute deviation from experiment (MAD) of 0.95 kcal mol-1, an improvement of 0.10 kcal mol-1 over G3 and G3X model chemistries. The performance of the ccCA on third-row-containing atoms and molecules is, therefore, commensurate in accuracy with previous studies on lighter main group elements H-Ar. While the typical methods used to compute theoretical molecular spin orbit corrections may go against the spirit of "black box" model chemistries, such corrections may be necessary for molecules containing heavy elements such as Ga-Kr. For example, when second-order spin orbit corrections are added to the atomic and molecular energies, the ccCA MAD is reduced to 0.88 kcal mol-1. digital.library.unt.edu/ark:/67531/metadc75422/
Aromatic C-H Activation and Catalytic Hydrophenylation of Ethylene by TpRu{P(OCH2)3CEt} (NCMe)Ph
This article discusses aromatic C-H activation and catalytic hydrophenylation of ethylene by TpRu{P(OCH2)3CEt} (NCMe)Ph. Abstract: The complexes TpRu{P(OCH2)3CEt}(L)R {L = PPh3 or NCMe; R = Cl, OTf (OTf = trifluoromethane-sulfonate), or Ph; Tp = hydridotris(pyrazolyl)borate} and TpRu{P(OCH2)3CEt} (ɳ3-C3H4Me) were synthesized and isolated. TpRu{P(OCH2)3CEt} (NCMe)Ph was found to initiate C-H activation of benzene and to catalyze the hydrophenylation of ethylene to produce ethylbenzene. Ethylene C-H activation to ultimately produce TpRu{P(OCH2)3CEt} (ɳ3-C3H4Me) kinetically competes with the catalytic hydrophenylation of ethylene. Computational studies were undertaken on reactions in the proposed catalytic ethylene hydrophenylation cycle as well as key side reactions. digital.library.unt.edu/ark:/67531/metadc77190/
Arylpalladium Phosphonate Complexes as Reactive Intermediates in Phosphorus-Carbon Bond Forming Reactions
This article discusses arylpalladium phosphonate complexes as reactive intermediates in phosphorus-carbon bond forming reactions. Abstract: Phosphorus-carbon bond formation from discrete transition metal complexes have been investigated through a combination of synthetic, spectroscopic, crystallographic, and computational methods. Reactive intermediates of the type (diphosphine)Pd(aryl)P(O)(OEt)2) have been prepared, characterized, and studied as possible intermediates in metal-mediated coupling reactions. Several of the reactive intermediates were characterized crystallographically, and a discussion of the solid state structures is presented. In contrast to other carbon-heteroelement bond forming reactions, palladium complexes containing electron-donating substituents on the aromatic fragment exhibited faster rates of reductive elimination. Large bit angle diphosphine ligands induced rapid rates of elimination, while bipyridine and small bite angle diphosphine ligands resulted in much slower rates of elimination. An investigation of the effect of typical impurities on the elimination reaction was carried out. While excess diphosphine, pyridine, and acetonitrile had little effect on the observed rate, the addition of water slowed the phosphorus-carbon bond forming reaction. Coordination of water to the complex was observed spectroscopically and crystallographically. Computational studies were utilized to probe the reaction pathways for P-C bond formation via Pd catalysis. digital.library.unt.edu/ark:/67531/metadc77191/
The Biological and Toxicological Activity of Gases and Vapors
This article discusses the biological and toxicological activity of gases and vapors. Abstract: A large amount of data on the biological and toxicological activity of gases and vapors has been collected from the literature. Processes include sensory irritation thresholds, the Alarie mouse test, inhalation anasthesia, etc. It is shown that a single equation using only five descriptors (properties of the gases and vapors) plus a set of indicator variables for the given processes can correlate 643 biological and non-lethal toxicological activities of 'non-reactive' compounds with a standard deviation of 0.36 log unit. The equation is scaled to sensory irritation thresholds obtained by the procedure of Cometto-Muñiz, and Cain, and provides a general equation for the prediction of sensory irritation thresholds in man. It is suggested that differences in biological/toxicological activity arise primarily from transport from the gas phase to a receptor phase or area, except for odor detection thresholds where interaction with a receptor(s) is important. digital.library.unt.edu/ark:/67531/metadc152441/
Bonding and Structure of Copper Nitrenes
This article discusses bonding and structure of copper nitrenes. Abstract: Copper nitrenes are of interest as intermediates in the catalytic aziridination of olefins and the amination of C-H bonds. However, despite advances in the isolation and study of late-transition-metal multiply bonded complexes, a bona fide structurally characterized example of a terminal copper nitrene has, to our knowledge, not been reported. In anticipation of such a report, terminal copper nitrenes are studied from a computational perspective. The nitrene complexes studied here are of the form (ß-diketiminate)Cu(NPh). Density functional theory (DFT), complete active space self-consistent-field (CASSCF) electronic structure techniques, and hybrid quantum mechanical/molecular mechanical (QM/MM) methods are employed to study such species. While DFT methods indicate that a triplet (S + 1) is the ground state, CASSCF calculations indicate the a singlet (S = 0) is the ground state, with only a small energy gap between the singlet and triplet. Moreover, the ground-state (open-shell) singlet copper nitrene is found to be highly multiconfigurational (i.e., biradical) and to possess a bent geometry about the nitrene nitrogen, contrasting with the linear nitrene geometry of the triplet copper nitrenes. CASSCF calculations also reveal the existence of a closed-shell singlet state with some degree of multiple bonding character for the copper-nitrene bond. digital.library.unt.edu/ark:/67531/metadc77132/
The Butterfly Dimer [(tBu3SiO)Cr]2 (μ-OSitBu3)2 and Its Oxidative Cleavage to (tBu3SiO)2 Cr(=N-N=CPh2)2 and (tBu3SiO)2 Cr=N(2,6-Ph2-C6H3)
This article discusses the butterfly dimer. Abstract: Treatment of CrCl2(THF)2 with NaOSitBu3 afforded the butterfly dimer [(tBu3SiO)Cr]2 (μ-OSitBu3)2 (1 2), whose d(CrCr) of 2.658(31) Å and magnetism were indicative of strong antiferromagnetic coupling. A Boltzmann distribution of low-energy 1A1, 3B1, 5A1, 7B1, and 9A1 states obtained from calculations on [(HO)2Cr]2(μOH)2 (1'2) were used to provide a reasonable fit of the μeff vs T data. Cleavage of 1 2 with various L (L=4-picoline, p-tolunitrile, tBuCN, tBuNC, Ph2CO, and PMe3) generated (tBu3SiO)2CrL2(1-L2). The dimer was oxidatively severed by Ph2CN2 to give (tBu3SiO)2Cr(N2CPh2)2 (2) and by RN3 at 23 ˚C to afford (silox)2Cr=NR (3-R) for bulky R (adamantyl (Ad), 2,6-iPr2-C6H3, 2,4,6-Me3-C6H2 = Mes, 2,6-Ph2-C6H3) and (tBu3SiO)2Cr(=NR)2 (4-R) for smaller substituents (R = 1-Naph, 2-Anth). X-ray structural studies were conducted on 1 2, square planar 1-(OCPh2)2, pseudo-Td 2 and pseudotrigonal 3-(2,6-Ph2-C6H3), whose S = 1 ground state was discussed on the basis of calculations of (H3SiO)2Cr = NPh (3"-Ph). digital.library.unt.edu/ark:/67531/metadc75425/
C-H Functionalization Reactivity of a Nickel-Imide
This article discusses C-H functionalization reactivity of a Nickel-Imide. Abstract: We report report bifunctional reactivity of the β-diketiminato Ni(III)-imide [Me₃NN]Ni=NAd (1), which undergoes H-atom abstraction (HAA) reactions with benzylic substrates R-H (indane, ethylbenzene, toluene). Nickel-imide 1 competes with the nickel-amide HAA product [Me₃NN]Ni-NHAd (2) for the resulting hydrocarbyl radical R• to give the nickel-amide [Me₃NN]Ni-N(CHMePh)Ad (3) (R-H = ethylbenzene) or aminoalkyl tautomer [Me₃NN]Ni(ɳ²-CH(Ph)NHAd) (4) (R-H = toluene). A significant amount of functionalized amine R-NHAd is observed in the reaction of 1 with indane along with the dinickel imide {[Me₃NN]Ni}₂(μ-NAd) (5). Kinetic and DFT analyses point to rate-limiting HAA from R-H by 1 to give R•, which may add to either imide 1 or amide 2, each featuring significant N-based radical character. Thus, these studies illustrate a fundamental competition possible in C-H amination systems that proceed via a HAA/radical rebound mechanism. digital.library.unt.edu/ark:/67531/metadc107790/
Calculation of a Methane C-H Oxidative Addition Trajectory: Comparison to Experiment and Methane Activation by High-Valent Complexes
This article discusses the calculation of a methane C-H oxidative addition trajectory. Abstract: An effective core potential (ECP), parallel supercomputing study of methane activation by 14-electron, Ir(PH₃)₂(X) complexes (X = H, Cl) is presented. Considerable weakening of the coordinated methane C-H bond occurs upon formation of an ɳ²-CH coordinated (X)(PH₃)₂Ir•••HCH₃ adduct. A more strongly bound adduct (with greater weakening of the coordinated C-H bond) occurs when X = Cl versus X = H. The calculated Ir(PH₃)₂(H) + CH₄ → Ir(PH₃)₂(H)₂(Me) reaction enthalpy is -12.8 kcal mol⁻¹, and -41.6 kcal mol⁻¹ for the chloro analogue. The intrinsic reaction coordinate is calculated and compared to an experimental trajectory. Analysis of the wave function along the intrinsic reaction coordinate (IRC) suggests that although donation of electron density from methane to metal is essential for adduct formation, it is not until backdonation to σ* сʜ increases that the C-H bond is activated and cleaved. The electronic and molecular structure of the reacting system along the IRC suggest a two-stage mechanism: substrate to complex donation is important in the early part of the reaction (electrophilic stage) while complex to substrate backdonation is necessary later on (nucleophilic stage) for C-H scission. Finally, comparison of IRCs for low- and high-valent methane-activating complexes shows similar topology in the early portion of the activation event; differentiation between oxidative addition and σ-bond metathesis occurs at the point at which there is a shift from the electrophilic to nucleophilic stage of the reaction. digital.library.unt.edu/ark:/67531/metadc107777/
Calculations of the Relative Energies of the 2B1g and 2A2u States of Cyclobutanetetraone Radical Cation and Radical Anion Provide Further Evidence of a 3B2u Ground State for the Neutral Molecule: A Proposed Experimental Test of the Prediction of a Triplet Ground State for (CO)4
This article discusses ground states. Abstract: B3LYP, CCSD(T), and CASPT2 calculations with the 6-311+G(2df) basis set have been performed on the radical anion and radical cation of cyclobutanetetraone (1). The very similar energies computed for the 2B1g and 2A2u states of both 1·+ and 1·- indicate that the singly occupied b1g and a2u MOs in these two states of the radical cation and anion have nearly the same energies, thus supporting the previously made prediction that neutral 1 has a 3B2u ground state. Reaction of squaric acid with O.(-), followed by negative ion photoelectron spectroscopy (NIPES) on the 1.(-) thus formed, is proposed as an experimental test of the startling prediction that tetraketone (1), a molecule that would be expected to be a closed-shell singlet, actually has a triplet ground state. digital.library.unt.edu/ark:/67531/metadc71812/
Calculations Predict a Large Inverse H/D Kinetic Isotope Effect on the Rate of Tunneling in the Ring Opening of Cyclopropylcarbinyl Radical
This article discusses calculations that predict a large inverse H/D kinetic isotope effect. Abstract: Tunneling rates are expected to decrease exponentially with the square root of the effective tunneling mass. Therefore, on substitution of a heavier for a lighter isotope, the observation of a large kinetic isotope effect (KIE), involving a substantial decrease in rate constant, is a commonly used diagnostic for a large contribution from quantum mechanical tunneling to a reaction. However, in this communication, the authors report the results of calculations that make the opposite prediction about some of the KIEs on the ring opening of cyclopropylcarbinyl radical (1) to 3-butene-1-y1 radical (2) by tunneling at cryogenic temperatures. Substitution of a heavier for a lighter isotope at the radical center (C1) of 1 is calculated to accelerate the rate of tunneling, giving KIEs at this carbon that are inverse. Of particular note is the authors' prediction that substitution of deuterium for both hydrogens at C1 will lead to a nearly 3-fold increase in the rate of reaction at temperatures so low that ring opening proceeds exclusively by tunneling from the lowest vibrational level. digital.library.unt.edu/ark:/67531/metadc71808/
Calculations Predict That Carbon Tunneling Allows the Degenerate Cope Rearrangement of Semibullvalene to Occur Rapidly at Cryogenic Temperatures
This article discusses carbon tunneling. Abstract: Calculations on the role of tunneling in the degenerate Cope rearrangements of semibullvalene (1) and barbaralane (3) predict that, at temperatures below 40 K, tunneling from the lowest vibrational level should make the temperature-independent rate constants k = 1.43 x 10(-3) s(-1) and k = 7.28 x 10(-9) s(-1), respectively. An experiment, using semibullvalene-2(4)-d1, is proposed to test the prediction of rapid tunneling by 1 at cryogenic temperatures. digital.library.unt.edu/ark:/67531/metadc71814/
Carbon-Hydrogen Bond Activation by Titanium Imido Complexes. Computational Evidence for the Role of Alkane Adducts in Selective C-H Activation
This article discusses carbon-hydrogen bond activation by Titanium imido complexes. Abstract: This paper reports calculations that probe the role of R (hydrocarbon) and R' (ligand substituent) effects on the reaction coordinate for C-H activation: Ti(OR')₂(=NR') + RH → adduct → transition state → (OR')₂Ti(N(H)R')(R). Compounds with R = H, Me, Et, Vy, cPr, Ph, Cy, Bz, and cubyl are studied using quantum (R' = H, SiH₃, SiMe₃) and classical (R' = SiᵗBu₃) techniques. Calculated geometries are in excellent agreement with data for experimental models. There is little variability in the calculated molecular structure of the reactants, products, and most interestingly, transition states as R and R' are changed. Structural flexibility is greatest in the adducts Ti(OR')₂(=NR')•••HR. Despite the small structural changes observed for Ti(OR')₂(=NR') with different R', significant changes are manifested in calculated electronic properties (the Mulliken charge on Ti becomes more positive and the Ti=N bond order decreases with larger R'), changes that should facilitate C-H activation. Substantial steric modification of the alkane complex is expected from R-R' interactions, given the magnitude of ∆Gadd and the conformational flexibility of the adduct. Molecular mechanics simulations of Ti(OSiᵗBu₃)₂(=NSiᵗBu₃)•••isopentane adducts yield an energy ordering as a function of the rank of the C-H bond coordinated to Ti that is consistent with experimental selectivity patterns. Calculated elimination barriers compare very favorably with experiment; larger SiH₃ and TMS ligand substituents generally yield better agreement with experiment, evidence that the modeling of the major contributions to the elimination barrier (N-H and C-H bond making) is ostensibly correct. Calculations indicate that weakening the C-H bond of the hydrocarbon yields a more strongly bound adduct. Combining the different conclusions, the present computational research points to the adduct, specifically the structure and energetics of the substrate/Ti-imido interaction, as the main factor in determining the selectivity of hydrocarbon (R) C-H activation. digital.library.unt.edu/ark:/67531/metadc107781/
Carbon-Oxygen Bond Formation via Organometallic Baeyer-Villiger Transformations: A Computational Study on the Impact of Metal Identity
This article discusses a computational study on the impact of metal identity. Abstract: Metal-mediated formation of C-O bonds is an important transformation that can occur by a variety of mechanisms. Recent studies suggest that oxygen-atom insertion into metal-hydrocarbyl bonds in a reaction that resembles the Baeyer-Villiger transformation is a viable process. In an effort to identify promising new systems, this study is designed to assess the impact of metal identity on such O-atom insertions for the reaction [(bpy)ₓM(Me)(OOH)]ⁿ → [(bpy)ₓM(OMe)(OH)]ⁿ (x = 1 or 2; bpy = 2,2'-bipyridyl; n is varied to maintain the d-electron count at d⁶ or d⁸). Six d⁸-square-planar complexes (M = Ptᴵᴵ, Pdᴵᴵ, Niᴵᴵ, Irᴵ, Rhᴵ, and Coᴵ) and eight d⁶-octahedral systems (M = Irᴵᴵᴵ, Rhᴵᴵᴵ, Coᴵᴵᴵ, Feᴵᴵ, Ruᴵᴵ, Osᴵᴵ, Mnᴵ, and Tcᴵ) are studied. Using density functional theory calculations, the structures and energies of ground-state and transition-state species are elucidated. This study shows clear trends in calculated ∆G‡'s for the O-atom insertions. The organometallic Baeyer-Villiger insertions are favored by lower coordination numbers (x = 1 versus x = 2), earlier transition metals, and first-row (3d) transition metals. digital.library.unt.edu/ark:/67531/metadc107789/
Catalytic Synthesis of Arylisocyanates from Nitroaromatics. A Computational Study
This article discusses catalytic synthesis of arylisocyanates from nitroaromatics. Abstract: Several conclusions of interest have emerged from a computational study of copper-catalyzed phenylisocyanate synthesis from nitrobenzene and carbon monoxide. Nitrobenzene complexes coordinate in a κ1-N fashion. With regard to thermodynamics, differences were observed for neutral (amidate, amidinate, β-diketiminate) versus cationic (diimine, NHC) complexes, although discernible trends were less evident for calculated kinetic barriers. The deoxygenation of the nitroso oxygen of the nitrosobenzene complex to form a copper-nitrene intermediate is postulated to be the rate-determining step. For the mechanism assumed in eqs 2 through 5, each step is exothermic. These individual steps are also calculated to possess reasonable kinetic barriers. Hence, copper-based complexes deserve consideration as potential catalysts for the phosgene-free synthesis of arylisocyanates from nitroaromatics. digital.library.unt.edu/ark:/67531/metadc77188/
Catalytic Tuning of a Phosphinoethane Ligand for Enhanced C-H Activation
This article discusses catalytic tuning of a phosphinoethane ligand for enhanced C-H activation. Abstract: Hydrogen atom abstraction (HAA) from 1,4-cyclohexadiene (CD-H) by (dtbpe)Ni(NAr) to form a Niǀ-amide, (dtbpe)Ni(NHAr), and cyclohexadienyl radical is calculated to be thermodynamically reasonable, ∆Hʜᴀᴀ(dtbpe) = -1.3 kcal/mol, dtbpe = bis(di-tert-butylphosphino)ethane, Ar = 2,6-diisopropylphenyl. However, radical rebound to form a metal-bound amine is highly endothermic (∆Hreb(dtbpe) = +25.1 kcal/mol). Analysis of bond enthalpies indicates that weakening of the Ni-N bond (Ni-amide→Ni-amine) upon radical rebound is not compensated by the weak C-N bond formed. Hence, a ligand was sought that would enhance the metal-amine bond strength while diminishing the metal-amide bond strength. Reaction of (dfmpe)Ni(NAr) with CD-H was thus analyzed, dfmpe = bis(di(trivluoromethyl)phosphino)ethane. While there is a small change in the thermodynamics of HAA (∆Hʜᴀᴀ(dfmpe) = -5.7 kcal/mol), there is a profound change in the rebound step (∆Hreb(dfmpe) = -7.8 kcal/mol) upon replacing dtbpe by dfmpe. Regeneration of the nitrene active species by reaction of ArN3 with the metal-bound product is calculated to be highly exothermic, ∆Hreg = -36.7 kcal/mol. Two candidates for a precatalyst, (dfmpe)Ni(COD) and (dfmpe)Ni(bpy), COD = 1,5-cyclooctadiene and bpy = 2,2´-bipyridine, were calculated to undergo highly exothermic reactions with ArN3 to form the nitrene active species. The calculated enthalpic barrier for HAA of CD-H by (dfmpe)Ni(NAr) is 21.3 kcal/mol. Hence, consideration of the computed thermodynamics and kinetics suggests that nickel-nitrenes with fluorinated phosphine supporting ligation are promising candidates for catalytic amination of C-H bonds. digital.library.unt.edu/ark:/67531/metadc77145/
Cation-specific and anion-specific Abraham model correlations for solute transfer into ionic liquid solvents
This article discusses cation-specific and anion-specific Abraham model correlations for solute transfer into ionic liquid solvents. Abstract: Data have been assembled from the published literature on the infinite dilution activity coefficients and gas solubilities of solutes dissolved in ionic liquid (IL) solvents. In total data for more than 1790 solute-IL pairs were compiled. The published experimental data were converted to gas-to-IL and water-to-IL partition coefficients, and correlated with the ion-specific equation coefficient version of the Abraham general solvation model. Ion-specific equation coefficients describe the experimental gas-to-IL and water-to-IL partition coefficient data to within 0.114 and 0.139 log units, respectively. Reported for the first time are equation coefficients for diethylphosphate, tris(pentafluoroethyl)trifluorophosphate and tetracyanoborate anions. digital.library.unt.edu/ark:/67531/metadc152450/
Characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model
This article discusses the characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model. Abstract: Water-to-polydimethylsiloxane (PDMS) and gas-to-PDMS sorption coefficients have been compiled for 170 gaseous and organic solutes. Both sets of sorption coefficients were analyzed using the Abraham solvation parameter model. Correlations were obtained for both "dry" headspace solid-phase microextraction and conventional "wet" PDMS coated surfaces. The derived equations correlated the experimental water-to-PDMS and gas-to-PDMS data to better than 0.17 and 0.18 log units, respectively. In the case of the gas-to-PDMS sorption coefficients, the experimental values spanned a range of approximately 11 log units. digital.library.unt.edu/ark:/67531/metadc155627/
Charge transfer equilibria in ambient-exposed epitaxial graphene on (0001) 6 H-SiC
This article discusses charge transfer equilibria in ambient-exposed epitaxial graphene on (0001) 6 H-SiC. Abstract: The transport properties of electronic materials have been long interpreted independently from both the underlying bulk-like behavior of the substrate or the influence of ambient gases. This is no longer the case for ultra-thin graphene whose properties are dominated by the interfaces between the active material and its surroundings. Here, the authors show that the graphene interactions with its environments are critical for the electrostatic and electrochemical equilibrium of the active device layers and their transport properties. Based on the prototypical case of epitaxial graphene on (0001) 6 H-SiC and using a combination of 'in-situ' thermoelectric power and resistance measurements and simulations from first principles, the authors demonstrate that the cooperative occurrence of an electrochemically mediated charge transfer from the graphene to air, combined with the peculiar electronic structure of the graphene/SiC interface, explains the wide variation of measured conductivity and charge carrier type found in prior reports. digital.library.unt.edu/ark:/67531/metadc132974/
Chemical Toxicity Correlations for Several Fish Species Based on the Abraham Solvation Parameter Model
This article discusses chemical toxicity correlations for several fish species based on the Abraham solvation parameter model. Abstract: The Abraham solvation parameter model is used to construct mathematical correlations for describing the nonspecific aquatic toxicity of organic compounds to the fathead minnow, guppy, bluegill, goldfish, golden orfe, and high-eyes medaka. The derived mathematical correlations describe the observed published toxicity data to within an overall average standard deviation of approximately 0.28 log units. In the case of ester solutes, the descriptions were improved by introducing an indicator variable into the basic model. Derived correlations can be used to estimate aquatic toxicities of organic chemicals to the six fish species studied and to help in identifying compounds whose toxic mode of action might involve chemical specific reactivity, rather than nonpolar or polar narcosis. A principle component analysis of the correlation equations shows that the water-octanol system is a poor model for nonspecific aquatic toxicity but that the water-isobutanol and water-pentanol systems are much better models. digital.library.unt.edu/ark:/67531/metadc152447/
Chemistry Surrounding Monomeric Copper(l) Methyl, Phenyl, Anilido, Ethoxide, and Phenoxide Complexes Supported by N-Heterocyclic Carbene Ligands: Reactivity Consistent with Both Early and Late Transition Metal Systems
This article discusses transition metal systems. Abstract: Monomeric copper(l) alkyl complexes that possess the N-heterocyclic carbene (NHC) ligands IPr, SIPr, and IMes [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] react with amines or alcohols to release alkane and form the corresponding monomeric copper(l) amido, alkoxide, or aryloxide complexes. Thermal decomposition reactions of (NHC)Cu׀ methyl complexes at temperatures between 100 and 130 °C produce methane, ethane, and ethylene. The reactions of (NHC)Cu(NHPh) complexes with bromoethane reveal increasing nucleophilic reactivity at the anilido ligand in the order (SIPR)Cu(NHPh) < (IPr)Cu(NHPh) < (IMes)Cu(NHPh) < (dtbpe)Cu(NHPh) [dtbpe = 1,2-bis(di-tert-butylphosphino)ethane]. DFT calculations suggest that the HOMO for the series of Cu anilido complexes is localized primarily on the amido nitrogen with some pπanilido-dπCu π*-character. [(IPr)Cu(μ-H)]2 and (IPr)Cu(Ph) react with aniline to quantitatively produce (IPr)Cu(NHPh)/dihydrogen and (IPr)Cu(NHPh)/benzene, respectively. Analysis of the DFT calculations reveals that the conversion of [(IPr)Cu(μ-H)]2 and aniline to (IPr)Cu(NHPh) and dihydrogen is favorable with ∆H ≈ -7 kcal/mol and ∆G ≈ -9 kcal/mol. digital.library.unt.edu/ark:/67531/metadc77128/
Cluster Core-Level Binding-Energy Shifts: The Role of Lattice Strain
This article discusses cluster core-level binding-energy shifts. Abstract: Our combined experimental and theoretical analysis of the shifts, with particle size, of core-level binding energies (BE's) of metal nanoparticles on insulating supports, shows that these shifts have an important initial state contribution arising, in large part, because of lattice strain. This contribution of BE shifts has not been recognized previously. Lattice strain changes the chemical bonding between the metal atoms and this change induces BE shifts. digital.library.unt.edu/ark:/67531/metadc78320/
CO₂ Reduction on Transition Metal (Fe, Co, Ni, and Cu) Surfaces: In Comparison with Homogeneous Catalysis
This article discusses CO₂ reduction on transition metal (Fe, Co, Ni, and Cu) surfaces. Abstract: Reduction of CO₂ to CO on Fe, Co, Ni, and Cu surfaces has been studied using density functional theory (DFT) methods. Three reaction steps were studied: (a) adsorption of CO₂ (M + CO₂/M) (M = transition metal surface), (b) decomposition of CO₂ (CO₂/M = (CO + O)/M), and (c) desorption of CO ((CO + O)/M = O/M + CO). Binding energies and reaction energies were calculated using the generalized gradient approximation (GGA) via the Perdew-Burke-Ernzerhof (PBE) functional. Calculations show an interesting trend for reaction energies and total reaction barriers, as a function of metal: from Fe to Cu, reactions tend to be less exergonic; the metals earlier in the 3d series have lower total barriers for CO₂ reduction. However, "overbinding" of CO₂ on Fe causes a thermodynamic sink on the reaction coordinate, adn Co and Ni are more favorable in terms of a smaller fluctuation in reaction energies/barriers for these elementary catalytic steps. A Brønsted-Evans-Polanyi (BEP) relationship was analyzed for C-O bond scission of CO₂ on the metal surfaces. Heterogeneous catalysis is also compared with the homogeneous models using transition metal β-diketiminato complexes, showing that both heterogeneous and homogeneous catalysis of CO₂ reduction display the same energetic trend as a function of metal. digital.library.unt.edu/ark:/67531/metadc107801/
Cobalt-Dinitrogen Complexes with Weakened N-N Bonds
This article discusses research on cobalt-dinitrogen complexes with weakened N-N bonds. Abstracts: Reported N₂ complexes of cobalt do not have substantial weakening of the N-N bond. Using diketiminate ligands to enforce three-coordinate geometries, we have synthesized several novel CoNNCo complexes. In formally univalent complexes, cobalt is poorer than iron at weakening the N-N bond, but in formally zerovalent complexes, cobalt and iron give similar N-N weakening. The weakening is due to cobalt-to-N₂ π-backbonding, and potassium cations pull more electron density into N₂. These results show that the low coordination number of a trigonal-planar geometry is impetus enough to make even the electronegative cobalt weaken the N-N bond of N₂. digital.library.unt.edu/ark:/67531/metadc107793/
Coinage Metal-Ethylene Complexes Supported by Tris(pyrazolyl)borates: A Computational Study
This article discusses coinage metal-ethylene complexes supported by tris(pyrazolyl)borates. Abstract: Data from computational and experimental sources have been combined to address the bonding and structure of [RB(3-(R1),5-(R2)Pz)3]M(C2H4) complexes, where M = Cu, Ag, Au. A k3 to k2 distortion of the scorpionate ligand was also studied. NMR properties were deemed to be the most useful in assessing the nature of the bonding in these complexes. Using computational recipes, 13C chemical shifts accurately reproduced quantitative experimental values and trends as a function of metal, ligand, and substituent. Au-ethylene complexes are found to be substantially "less π-complex" (T-shaped structure) in their bonding description versus Ag and Cu congeners, although the former are by no means entirely metallacyclopropane in their constitution. Combining the present calculations with prior contributions to coinage metal bonding leads the authors to propose that similarity of molecular structure among a congeneric series of coinage metal complexes reflects a principally ionic coinage metal-ligand bonding regime, while dissimilarity of structure within the series reflects a primarily covalent bonding regime. digital.library.unt.edu/ark:/67531/metadc77192/
Combined Experimental and Computational Studies on the Nature of Aromatic C-H Activation by Octahedral Ruthenium(II) Complexes: Evidence for σ-Bond Metathesis from Hammett Studies
This article discusses combined experimental and computational studies on the nature of aromatic C-H activation by octahedral ruthenium(II) complexes. Abstract: Octahedral ruthenium complexes of the type TpRu(L)(NCMe)R [Tp = hydridotris(pyrazolyl)borate; R = alkyl or aryl; L = CO or PMe3] have been shown previously to initiate the C-H activation of aromatic substrates. In order to probe the nature of the C-H activation step, reaction rates have been theoretically obtained for the conversion of TpRu(L)(ƞ2-C,C-C6H5X)Me to TpRu(L)(ρ-C6H4X) and CH4 where X is varied among Br, Cl, CN, F, H, NH2, NO2, and OMe. A linear Hammett correlation is calculated with a positive ρ value of 2.6 for L = CO and 3.2 for L = PMe3. Calculated kinetic data for the aromatic C-H activations indicate that an electrophilic aromatic substitution mechanism is unlikely. While experiments cannot fully replicate the entire range of calculated Hammett plots, reactivity trends are consistent with the calculations that suggest activation barriers to overall metal-mediated arene C-H bond cleavage are reduced by the presence of electron-withdrawing groups in the position para to the site of activation. Previous mechanistic studies, as well as the structure and imaginary vibrational modes of the present transition states, validate that the C-H activation for this family of TpRu complexes occurs through a σ-bond metathesis-type pathway. digital.library.unt.edu/ark:/67531/metadc83332/
Combined Experimental and Computational Study of TpRu{P(pyr)3} (NCMe)Me (pyr = N-pyrrolyl): Inter- and Intramolecular Activation of C-H Bonds and the Impact of Sterics on Catalytic Hydroarylation of Olefins
This article discusses a combined experimental and computational study of TpRu{P(pyr)3} (NCMe)Me (pyr = N-pyrrolyl). Abstract: Complexes of the type TpRu{P(pyr)3} (L)R {L = PPh3 or NCMe; R = Cl, OTf = trifluoromethanesulfonate), Me, or Ph; Tp = hydridotris(pyrazolyl)borate; pyr = N-pyrrolyl} and TpRu-{κ2-P, C-P(pyr)2(NC4H3)}NCMe. TpRu{P(pyr)3}(NCMe)Ph catalyzes the hydrophenylation of ethylene in benzene to produce ethylene by TpRu{P(pyr)3}(NCMe)Ph suggest that inefficient catalysis is not due to difficulty in the C-H activation of benzene by the active catalyst species, but rather likely arises from the steric bulk of the tris-N-pyrrolyl phosphine ligand, which inhibits coordination of ethylene and thus thwarts c-C bond formation. digital.library.unt.edu/ark:/67531/metadc77189/
Comment on the Prediction of Gas Chromatographic Retention Behavior with Mixed Liquid Phases
This article comments on the prediction of gas chromatographic retention behavior with mixed liquid phases. digital.library.unt.edu/ark:/67531/metadc146582/
Comments on the Competitive Preferential Solvation Theory
This article offers comments on the competitive preferential solvation theory. Abstract: Simple additive relationships for the physico-chemical properties of a solute dissolved in binary solvent mixtures are developed from the competitive preferential solvation model. Additive expressions for solute mole fraction solubility and logarithm of solute solubility are mathematically identical to equations derived previously from the microscopic partition and basic nearly ideal binary solvent models. Calculated values based on the various additive relationships are compared to carbazole solubilities in ten binary solvent mixtures containing dibutyl ether with n-hexane, n-heptane, n-octane, cyclohexane, cyclo-octane, methylcyclohexane, iso-octane, n-hexadecane, squalane and t-butylcyclohexane. digital.library.unt.edu/ark:/67531/metadc157300/
Comparative Reactivity of TpRu(L)(NCMe)Ph (L = CO or PMe3): Impact of Ancillary Ligand L on Activation of Carbon-Hydrogen Bonds Including Catalytic Hydroarylation and Hydrovinylation/Oligomerization of Ethylene
This article discusses comparative reactivity of TpRu(L)(NCMe)Ph (L = CO or PMe3). Abstract: Complexes of the type TpRu(L)(NCMe)R [L = CO or PMe3; R = Ph or Me; Tp = hydridotris-(pyrazolyl)borate] initiate C-H activation of benzene. Kinetic studies, isotopic labeling, and other experimental evidence suggest that the mechanism of benzene C-H activation involves reversible dissociation of acetonitrile, reversible benzene coordination, and rate-determining C-H activation of coordinated benzene. TpRu(PMe3)(NCMe)Ph initiates C-D activation of C6D6 at rates that are approximately 2-3 times more rapid than that for TpRu(CO)(NCMe)Ph (depending on substrate concentration); however, the catalytic hydrophenylation of ethylene using TpRu(PMe3)(NCMe)Ph is substantially less efficient than catalysis with TpRu(CO)(NCMe)Ph. For TpRu(PMe3)(NCMe)Ph, C-H activation of ethylene, to ultimately produce TpRu-(PMe3)(ɳ3-C4H7), is found to kinetically compete with catalytic ethylene hydrophenylation. In THF solutions containing ethylene, TpRu(PMe3)(NCMe)Ph and TpRu(CO)(NCMe)Ph separately convert to TpRu(L)(ɳ3-C4H7)(L = PMe3 or CO, respectively) via initial Ru-mediated ethylene C-H activation. Heating mesitylene solutions of TpRu(L)(ɳ3-C4H7) under ethylene pressure results in the catalytic production of butenes (i.e., ethylene hydrovinylation) and hexenes. digital.library.unt.edu/ark:/67531/metadc77140/
Complex Materials for Molecular Spintronics Applications: Cobalt Bis(dioxolene) Valence Tautomers, from Molecules to Polymers
This article discusses complex materials for molecular spintronics applications. Abstract: Using first principles calculations, the authors predict a complex multifunctional behavior in cobalt bis(dioxolene) valence tautomeric compounds. Molecular spin-state switching is shown to dramatically alter electronic properties and corresponding transport properties. This spin state dependence has been demonstrated for technologically relevant coordination polymers of valence tautomers as well as for novel conjugated polymers with valence tautomeric functionalization. As a result, these materials are proposed as promising candidates for spintronic devices that can couple magnetic bistability with novel electrical and spin conduction properties. The authors' findings pave the way to the fundamental understanding and future design of active multifunctional organic materials for spintronics applications. digital.library.unt.edu/ark:/67531/metadc132994/
Computational s-Block Thermochemistry with the Correlation Consistent Composite Approach
This article discusses computational s-block thermochemistry with the correlation consistent composite approach. Abstract: The correlation consistent composite approach (ccCA) is a model chemistry that has been shown to accurately compute gas-phase enthalpies of formation for alkali and alkaline earth metal oxides and hydroxides (Ho, D.S.; DeYonker, N.J.; Wilson, A.K.; Cundari, T.R., J. Phys. Chem. A 2006, 110, 9767). The ccCA results contrast to more widely used model chemistries where calculated enthalpies of formation for such species can be in error by up to 90 kcal molˉ¹. In this study, the authors have applied ccCA to a more general set of 42 s-block molecules and compared the ccCA ∆Hf values to values obtained using the G3 and G3B model chemistries. Included in this training set are water complexes such as Na(H₂O)n⁺ where n = 1 - 4, dimers and trimers of ionic compounds such as (LiCl)₂ and (LiCl)₃, and the largest ccCA computation to date: Be-(acac)₂, BeC₁₀H₁₄O₄. Problems with the G3 model chemistries seem to be isolated to metal-oxygen bonded systems and Be-containing systems, as G3 and G3B still perform quite well with a 2.7 and 2.6 kcal mol⁻¹ mean absolute deviation (MAD), respectively, for gas-phase enthalpies of formation. The MAD of the ccCA is only 2.2 kcal mol⁻¹ for enthalpies of formation (∆ Hf) for all compounds studied herein. While this MAD is roughly double that found for a ccCA study of >350 main group (i.e., p-block) compounds, it is commensurate with typical experimental uncertainties for s-block complexes. Some molecules where G3/G3B and ccCA computed ∆Hf values deviate significantly from experiment, such as (LiCl)₃, NaCN, and MgF, are inviting candidates for new experimental and high-level theoretical studies. digital.library.unt.edu/ark:/67531/metadc77174/
Computational Study of Polarizabilities and Second Hyperpolarizabilities of Inorganic Transition Metal Thiometalates and Metalates in Solution
This article discusses a computational study of polarizabilities and second hyperpolarizabilities of inorganic transition metal thiometalates and metalates in solution. Abstract: A systematic study of nonlinear optical (NLO) properties of inorganic transition metal (TM) thiometalates and metalates is reported. Polarizabilities (α) and second hyperpolarizabilities (y) are calculated in solution within the polarizable continuum model. It is found that NLO properties of anionic inorganic complexes can be successfully modeled in solution, when this cannot be done so in the gas phase. Solvent effects are found to significantly increase α and y. The effects are stronger on y (up to 80%) than on α (up to 40%) and stronger on TM thiometalates than on metalates. For α, solvent effects are found to be more important than electron correlation effects. For y, the two effects are similarly important. Solvent effects on α and y caused by subordinate factors other than the dominant electrostatic solute-solvent interactions were studied and assessed to be negligible. Upon solvation, large TM and ligand modification effects on α and y are found. One oxo-to-sulfido substitution results in an increase in α by 38 au and y by 10 000 au. digital.library.unt.edu/ark:/67531/metadc107806/
Conversions of Ruthenium (III) Alkyl Complexes to Ruthenium (II) through Ru-Calkyl Bond Homolysis
This article discusses conversions of Ruthenium(III) alkyl complexes. Abstract: Single-electron oxidation of the Ru(II) complexes TpRu(L)(L')(R) (L = CO, L' = NCMe, and R = CH3 or CH2CH2Ph; L = L' = PMe3 and R = CH3) with AgOTf leads to alkyl elimination reactions that produce TpRu(L)(L')(OTf) and organic products that likely result from Ru-Calkyl bond homolysis. Density functional calculations on TpRu(CO)(NCMe)(Me) and its Ru(III) cation indicate that the Ru-CH3 homolytic bond dissocation enthalpy is substantially reduced (48.6 to 23.2 kcal/mol) upon oxidation. digital.library.unt.edu/ark:/67531/metadc77179/
Cooperative Effects in the Annelation of Benzene by Multiple Etheno Groups
This article discusses cooperative effects in the annelation of benzene by multiple etheno groups. Abstract: The results of B3LYP/6-31G(d) calculations show that there is a strong cooperative effect on the energies that result from annelating benzene with 1, 2, and 3 etheno groups, to form 3, 4, and 5 respectively. The etheno annelation energies have been decomposed into two major contributors - etheno annelation, with all the bonds in the six-membered ring constrained to have the same C-C bond length as in D6h benzene, and optimization of the C-C bond lengths in the annelated benzene ring. The energies computed for each of these two steps show that the etheno groups behave cooperatively in both of them. The origin of the cooperativity, calculated for each step, is described and discussed. digital.library.unt.edu/ark:/67531/metadc71793/
Correlation and prediction of partition coefficient between the gas phase and water, and the solvents dry methyl acetate, dry and wet ethyl acetate, and dry and wet butyl acetate
This article discusses the correlation and prediction of partition coefficient between the gas phase and water, and the solvents dry methyl acetate, dry and wet ethyl acetate, and dry and wet butyl acetate. Abstract: Experimental partition coefficient data have been compiled from the published literature for the water/methyl acetate, water/ethyl acetate and water/butyl acetate partition systems, log P data, and for the gas/methyl acetate, gas/ethyl acetate and gas/butyl acetate partition systems, log K data. Application of the Abraham solvation parameter model to the sets of partition coefficients leads to equations that correlate the log P data and log K data to 0.18 log units for the three dry alkyl acetate solvents. Slightly larger deviations were noted for solute partition into both wet ethyl acetate and wet butyl acetate. The derived correlations were validated using training set and test set analyses. digital.library.unt.edu/ark:/67531/metadc155629/
Correlation and prediction of solute transfer to chloroalkanes from both water and the gas phase
This article discusses the correlation and prediction of solute transfer to chloroalkanes from both water and the gas phase. Data have been compiled from the published literature on the partition coefficients of solutes and vapors into chloroform, carbon tetrachloride, dichloromethane and 1-chlorobutane from both water and from the gas phase. The logarithms of the water-to-chloroalkane (log P) and gas-to-chloroalkane partition coefficients (log K) are correlated with the Abraham solvation parameter model. The derived correlations describe the observed log P and log K values within standard deviations of about 0.13-0.20 log units. For chloroform and carbon tetrachloride, the derived correlations were validated using training set and test set analyses. digital.library.unt.edu/ark:/67531/metadc155630/
The correlation-consistent composite approach: Application to the G3/99 test set
This article discusses the correlation-consistent composite approach. Abstract: The correlation-consistent composite approach (ccCA), an ab initio composite technique for computing atomic and molecular energies, recently has been shown to successfully reproduce experimental data for a number of systems. The ccCA is applied to the G3/99 test set, which includes 223 enthalpies of formation, 88 adiabatic ionization potentials, 58 adiabatic electron affinities, and 8 adiabatic proton affinities. Improvements on the original ccCA formalism include replacing the small basis set quadratic configuration interaction computation with a coupled cluster computation, employing a correction for scalar relativistic effects, utilizing the tight-d forms of the second-row correlation-consistent basis set extrapolation of MP2 energies, ccCA results in an almost zero mean deviation for the G3/99 set (with a best value of -0.10 kcal molˉ¹), and a 0.96 kcal molˉ¹ mean absolute deviation, which is equivalent to the accuracy of the G3X model chemistry. There are no optimized or empirical parameters included in the computation of ccCA energies. Except for a few systems to be discussed, ccCA performs as well as or better than Gn methods for most systems containing first-row atoms, while for systems containing second-row atoms, ccCA is an improvement over Gn model chemistries. digital.library.unt.edu/ark:/67531/metadc75420/
The correlation consistent composite approach (ccCA): An alternative to the Gaussian-n methods
This article discusses the correlation consistent composite approach (ccCA). Abstract: An alternative to the Gaussian-n (G1, G2, and G3) composite methods of computing molecular energies is proposed and is named the "correlation consistent composite approach" (ccCA, ccCA-CBS-1, ccCA-CBS-2). This approach uses the correlation consistent polarized valence (cc-pVXZ) basis sets. The G2-1 test set of 48 enthalpies of formation (∆Hf), 38 adiabatic ionization potentials (IPs), 25 adiabatic electron affinities (EAs), and 8 adiabatic proton affinities (PAs) are computed using this approach, as well as the ∆Hf values of 30 more systems. Equilibrium molecular geometries and vibrational frequencies are obtained using B3LYP density functional theory. When applying the ccCA-CBS method with the cc-pVXZ series of basis sets augmented with diffuse functions, mean absolute deviations within the G2-1 test set compared to experiment are 1.33 kcal molˉ¹ for ∆Hf, 0.81 kcal molˉ¹ for IPs, 1.02 kcal molˉ¹ for EAs, and 1.51 kcal molˉ¹ for PAs, without including the "high-level correction" (HLC) contained in the original Gn methods. Whereas the HLC originated in the Gaussian-1 method as an isogyric correction, it evolved into a fitted parameter that minimized the error of the composite methods, eliminating its physical meaning. Recomputing the G1 and G3 enthalpies of formation without the HLC reveals a systematic trend where most ∆Hf values are significantly higher than experimental values. By extrapolating electronic energies to the complete basis set (CBS) limit and adding G3-like corrections for the core-valence and infinite-order electron correlation effects, ccCA-CBS-2 often underestimates the experimental ∆Hf, especially for larger systems. This is desired as inclusion of relativistic and atomic spin-orbit effects subsequently improves theoretical ∆Hf values to give a 0.81 kcal molˉ¹ mean absolute deviation with ccCA-CBS-2. The ccCA-CBS method is a viable "black box" method that can be used on systems with at least 10-15 heavy atoms. digital.library.unt.edu/ark:/67531/metadc75421/
Correlation of solute transfer into alkane solvents from water and from the gas phase with updated Abraham model equations
This article discusses the correlation of solute transfer into alkane solvents from water and from the gas phase with updated Abraham model equations. Abstract: Literature data regarding partitioning of compounds from the gas phase to alkanes and from water to alkanes have been compiled and analyzed in accord with the Abraham solvation parameter model. Mathematical correlations have been developed for describing the partitioning behavior of organic solutes and gases into hexane, heptane, octane and decane. Derived mathematical expressions were found to predict the available partition coefficient data to within 0.15 log units or better. digital.library.unt.edu/ark:/67531/metadc152452/
Correlation of Solute Transfer Into Toluene and Ethylbenzene from Water and from the Gas Phase Based on the Abraham Model
This article discusses correlation of solute transfer into toluene and ethylbenzene from water and from the gas phase based on the Abraham model. Experimental data have been compiled from the published literature on the partition coefficients of solutes and vapors into ethylbenzene and toluene at 298 K. The logarithms of the water-to-ethylbenzene and water-to-toluene partition coefficients, log P, and gas-to-ehtylbenzene and gas-to-toluene partition coefficients, log K, were correlated with the Abraham solvation parameter model. The derived mathematical expressions described the observed log P and log K data for the two aromatic hydrocarbon solvents to within average deviations of 0.13 log units or less. digital.library.unt.edu/ark:/67531/metadc152451/
Current Applications of Computational Chemistry in JACS - Molecules, Mechanisms, and Materials
This article discusses current applications of computational chemistry. This virtual issue of JACS Select is devoted to some of the computation chemistry that has recently been published in the Journal of the American Chemical Society (JACS). The 25 articles and Communications that appear in this issue of JACS Select were chosen on the basis of the enthusiasm of the referees for these manuscripts when they were reviewed, as well as on the number of times each of these articles has been accessed online since its publication. Diversity of subject matter was not a criterion used in selecting these 25 articles from the ca. 50 well-reviewed, frequently accessed articles that were initially considered. However, inspection of the list of the subjects covered - from amyloid fibril polymorphism to nucleation of amorphous calcium carbonate; from the structure of solid Li(NH3)4 to the role that solvation plays in the Thorpe-Ingold effect; and to the nonstatistical, gas-phase dynamics of [1,5] hydrogen shifts in chemically activated cyclopentadiene - reveals the diverse nature of some of the best papers in computational chemistry that have been published recently in JACS. digital.library.unt.edu/ark:/67531/metadc71807/
Cyclooctatetraenes Tetrakis-Annelated with α-Dithio- or α-Diselenocarbonyl Groups: Diradicals Predicted To Have Ground States with 10 π Electrons in the Eight-Membered Ring and Two-Center, Three-Electron, σ Bonds between Two Pairs of Chalcogen Atoms
This article discusses cyclooctatetraenes. Abstract: (U)B3LYP calculations with the 6-31+G(d) and 6-311+G(2df) basis sets have been carried out on cyclooctatetraenes 6 and 7, in which the COT ring is tetrakis-annelated with α-dithio- or α-diselenocarbonyl groups. Transferring two electrons from the high-lying b1g and eu σ MOs in 6 and 7 into the unoccupied, nonbonding, COT π orbital is computed to be energetically favorable. The lowest D4h electronic state is calculated to be 3Eu, which formally contains 10 π electrons in the eight-membered ring and has two unpaired electrons in σ MOs. The 3Eu state undergoes a first-order Jahn-Teller distortion to form 6d and 7d, in which the pair of one-electron holes in the σ MOs is stabilized by the formation of two, two-center, three-electron bonds between pairs of chalcogen atoms that are diagonally across the eight-membered ring from each other. The corresponding open-shell singlets are computed to be about 1 kcal/mol lower in energy than the Jahn-Teller distorted triplets. Molecules 6i and 7i, in which the C-C bond in one four-membered ring is cleaved, are computed to be lower in energy than 6d and 7d. However, a substantial barrier is predicted to separate each of the two pairs of isomers so that 6d and 7d should, at least in principle, be isolable. digital.library.unt.edu/ark:/67531/metadc71813/
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