Enthalpy of solvation correlations for gaseous solutes dissolved in dimethyl sulfoxide and propylene carbonate based on the Abraham model
Date: July 2007
Creator: Mintz, Christina; Acree, William E. (William Eugene); Burton, Katherine & Abraham, M. H. (Michael H.)
Description: This article discusses enthalpy of solvation correlations for gaseous solutes dissolved in dimethyl sulfoxide and propylene carbonate based on the Abraham model. Abstract: Data have been assembled from the published literature on the enthalpies of solvation for more than 100 compounds in dimethyl sulfoxide and propylene carbonate. It is shown that an Abraham solvation equation with five descriptors can be used to correlate the experimental solvation enthalpies to within standard deviations of 2.80 and 2.61 kJ/mol for dimethyl sulfoxide and propylene carbonate, respectively. The derived correlations provide very accurate mathematical descriptions of the measured enthalpy of solvation data at 298 K, which in the case of dimethyl sulfoxide span a range of about 92 kJ/mol. Division of the experimental values into a training set and a test set shows that there is no bias in predictions, and that the predictive capability of the correlations is better than 3.6 kJ/mol.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc155626/
Enthalpy of solvation correlations for gaseous solutes dissolved in chloroform and 1,2-dichloroethane based on the Abraham model
Date: September 15, 2007
Creator: Mintz, Christina; Burton, Katherine; Acree, William E. (William Eugene) & Abraham, M. H. (Michael H.)
Description: This article discusses enthalpy of solvation correlations for gaseous solutes dissolved in chloroform and 1,2-dichloroethane based on the Abraham model. Abstract: Enthalpy of solvation data have been compiled from the published literature for more than 80 solutes dissolved in chloroform and 1,2-dichloromethane. Mathematical correlations based on the Abraham general solvation parameter model are developed for describing the experimental solvation enthalpies to within standard deviations of 2.10 kJ/mol (chloroform) and 1.72 kJ/mol (1,2-dichloroethane). Division of the measured values into a training set and a test set shows that there is no bias in predictions, and that the estimative capability of the correlations is better than 2.5 kJ/mol.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc155628/
Evaluation Of WEPP For Runoff And Sediment Yield Prediction On Natural Gas Well Sites
Date: 2008
Creator: Wachal, David J.; Harmel, R. Daren; Banks, Kenneth E. & Hudak, Paul F.
Description: This article discusses the evaluation of WEPP for runoff and sediment yield prediction on natural gas well sites. Abstract: Natural gas exploration and production requires land-disturbing construction activities that have the potential to accelerate soil loss due to land cover modifications, increased slopes, and flow concentration. In the U.S., nearly 30,000 new gas wells are drilled each year. Erosion modeling has been successfully used for decades to predict soil loss and conservation effects on agricultural fields, rangelands, and forests, although much less research has been conducted on the application of erosion models for disturbed construction site conditions. The objective of this research was to evaluate Water Erosion Prediction Project (WEPP) runoff and sediment yield predictions relative to measured data from two natural gas well sites (referred to as GW1 and GW2) in north central Texas. Model parameters were adjusted from WEPP default parameters based on available literature and model observations. A low effective hydraulic conductivity value (0.75 mm h⁻¹) resulted in successful runoff predictions. Agreement between predicted and measured sediment yields was accomplished by increasing rill and interrill erodibility values and decreasing critical shear stress values from default values. WEPP performance was evaluated with the Nash-Sutcliffe efficiency (NSE), root mean ...
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc155619/
Oxygen Atom Transfer Energetics: Assessment of the Effect of Method and Solvent
Date: February 23, 2006
Creator: Dinescu, Adriana; Whiteley, Clinton; Combs, Rachel R. & Cundari, Thomas R., 1964-
Description: This article discusses oxygen atom transfer energetics. Abstract: Several density functional methods, the semiempirical methods AM1 and PM3, Hartree-Fock, and Gaussian3 theories were applied to compute the oxygen atom transfer enthalpies for 14 X/XO couples (inorganic and organic systems, charged and neutral species, light and heavy main group element containing molecules). The calculated reaction enthalpies were compared to available experimental data. The G3 method alone was found to perform within the experimental error, while the popular B3LYP and BLYP functionals provided inadequate results. Solvent effects were estimated for 19 neutral and anionic X/XO couples by using the conductor-like polarizable continuum model and several cavity models coupled with the B3LYP/6-31++G-(2d,2p) level of theory. Surprisingly, the magnitude of the aqueous solvent correction was found to vary significantly for different solute cavity models, occasionally giving larger errors than the gas-phase calculation.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc77147/
On Bär's Conformal Lower Bound for the Spectrum of Generalized Dirac Operators
Date: 2000
Creator: Anghel, Nicolae
Description: This article discusses Bär's conformal lower bound for the spectrum of generalized Dirac operators. Abstract: We use the orthogonal splitting of a certain Clifford module as a direct sum of generalized spinors and twistors to give a short and natural proof to Bär's conformal lower bound for the spectrum of a generalized Dirac operator on a compact Riemannian manifold.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc161690/
Molybdenum and Tungsten Structural Differences are Dependent on ndz2/(n + 1)ѕ Mixing: Comparisons of (silox)3MX/R (M = Mo, W; silox = tBu3SiO)
Date: July 15, 2008
Creator: Kuiper, David S.; Douthwalte, Richard E.; Mayoi, Ana-Rita; Wolczanski, Peter T.; Lobkovsky, Emil B.; Cundari, Thomas R., 1964- et al
Description: This article discusses molydbenum and tungsten structural differences. Abstract: Treatment of trans-(Et2O)2MoCI4 with 2 or 3 equiv of Na(silox) (i.e., NaOSitBu3) afforded (silox)3MoCI2 (1-Mo) or (silox)3MoCI (2-Mo). Purification of 2-Mo was accomplished via addition of PMe3 to precipitate (silox)3CIMoPMe3 (2-MoPMe3), followed by thermolysis to remove phosphine. Use of MoCI3(THF)3 with various amounts of Na(silox) produced (silox)2CIMoMoCI(silox)2 (3-Mo). Alkylation of 2-Mo with MeMgBr or EtMgBr afforded (silox)3MoH, which was prepared from 2-Mo and NaBEt3H. Thermolysis of WCI6 with HOSitBu3 afforded (silox)2WCI4 (4-W), and sequential treatment of 4-W with Na/Hg and Na(silox) provided (silox)3WCI2 (1-W, tbp, X-ray), which was alternatively prepared from trans-(Et2S)2WCI4 and 3 equiv of TI(silox). Na/Hg reduction of 1-W generated (silox)3WCI (2-W). Alkylation of 2-W with MeMgBr produced (silox)3WMe (2-WMe), which dehydrogenated to (silox)3WCH (6-W) with ∆ H‡ = 14.9(9) kcal/mol and ∆S‡ = -26(2) eu. Magnetism and structural studies revealed that 2-Mo and 2-MoEt have triplet ground states (GS) and distorted trigonal monopyramid (tmp) and tmp structures, respectively. In contrast, 2-W and 2-WMe possess squashed-Td (distorted square planar) structures, and the former has a singlet GS. Quantum mechanics/ molecular mechanics studies of the S = 0 and S = 1 states are full models of 2-Mo, 2-MoEt, 2-W, ...
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc77130/
Microwave absorption by an array of carbon nanotubes: A phenomenological model
Date: August 29, 2006
Creator: Ye, Z.; Deering, William D.; Krokhin, Arkadii A. & Roberts, James
Description: This article discusses microwave absorption by an array of carbon nanotubes. Abstract: A simple model to explain microwave-induced heating of carbon nanotubes (CNTs) through transformation of electromagnetic energy into mechanical vibrations is proposed and analyzed. The model provides a way to understand recent observations of heating of CNTs exposed to microwaves in the range of 2-20 GHz. It is shown that transverse vibrations of CNTs during microwave irradiation can be associated with parametric resonance, as occurs in the analysis of acoustic experiments on forced longitudinal vibrations of a stretched elastic string. For carbon nanotubes [single wall nanotube (SWNT), double wall nanotube (DWNT), multiwall nanotube (MWNT), ropes, and strands] the resonant parameters are shown to be located in a region of instability of the Mathieu's equation. Wave equations with cubic nonlinearity were used to qualitatively describe the effects of phonon-phonon interactions and energy transfer from microwaves to CNTs at a rate much exceeding the traditional Joule heating via electron-phonon interaction.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc103271/
Characterization of the sorption of gaseous and organic solutes onto polydimethyl siloxane solid-phase microextraction surfaces using the Abraham model
Date: December 21, 2007
Creator: Sprunger, Laura M.; Proctor, Amy; Acree, William E. (William Eugene) & Abraham, M. H. (Michael H.)
Description: 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.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc155627/
Olefin Substitution in (silox)3M(olefin) (silox = tBu3SiO; M = Nb, Ta): The Role of Density of States in Second vs Third Row Transition Metal Reactivity
Date: January 8, 2008
Creator: Hirsekorn, Kurt F.; Hulley, Elliott B.; Wolczanski, Peter T. & Cundari, Thomas R., 1964-
Description: This article discusses the role of density of states in second vs third row transition metal reactivity. Abstract: The substitution chemistry of olefin complexes (silox)3M(ole) (silox = tBu3SiO; M = Nb (1-ole), Ta (2-ole); ole = C2H4 (as 13C2H4 or C2D4), C2H3Me, C2H3Et, cis-2-C4H8, iso-C4H8, C2H3Ph, cC5H8, cC6H10, cC7H10 (norbornene)) was investigated. For 1-ole, substitution was dissociative (∆Gǂdiss), and in combination with calculated olefin binding free energies (∆G˚bind), activation free energies for olefin association (∆Gǂassoc) to (silox)3Nb (1) were estimated. For 2-ole, substitution was not observed prior to rearrangement to alkylidenes. Instead, activation free energies for olefin association to (silox)3Ta (2) were measured, and when combined with ∆G˚bind(calcd), estimates of olefin dissociation rates from 2-ole were obtained. Despite stronger binding energies for 1-ole vs 2-ole, the dissociation of olefins from 1-ole is much faster than that from 2-ole. The association of olefins to 1 is also much faster than that to 2. Linear free energy relationships (with respect to ∆G˚bind) characterize olefin dissociation from 1-ole, but not olefin dissociation from 2-ole, and olefin association to 2, but not olefin association to 1. Calculated transition states for olefin dissocation from (HO)3M(C2H4) (M = Nb, 1´-C2H4; Ta, 2´-C2H4) are asymmetric and have ...
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc77142/
Octahedral [TpRu(PMe3)2OR]n+ Complexes (Tp = hydridotris(pyrazolyl)borate; R = H or Ph; n = 0 or 1): Reactions at Ru(II) and Ru(III) Oxidation States with Substrates that Possess Carbon-Hydrogen Bonds
Date: September 15, 2006
Creator: Feng, Yuee; Gunnoe, T. Brent; Grimes, Thomas V. & Cundari, Thomas R., 1964-
Description: This article discusses octahedral [TpRu(PMe3)2OR]n+ Complexes (Tp = hydridotris(pyrazolyl)borate. Abstract: The Ru(II) complexes TpRu(PMe3)2OR (R = H or Ph) react with excess phenylacetylene at elevated temperatures to produce the phenylacetylide complex TpRu(PMe3)2(C≡CPh). Kinetic studies indicate that the reaction of TpRu(PMe3)2OH and phenylacetylene likely proceeds through a pathway that involves TpRu(PMe3)2OTf as a catalyst. The reaction of TpRu(PMe3)2OH with 1,4-cyclohexadiene at elevated temperature forms benzene and TpRu(PMe3)2H, while TpRu(PMe3)2OPh does not react with 1,4-cyclohexadiene even after 20 days at 80 ˚C. The paramagnetic Ru(III) complex [TpRu(PMe3)2OH][OTf] is formed upon single-electron oxidation of TpRu(PMe3)2OH with AgOTf. Reactivity studies suggest that [TpRu(PMe3)2OH][OTf] initiates reactions, including hydrogen atom abstraction, with C-H bonds that have bond dissociation energy < 80 kcal/mol. Experimentally, the O-H bond strength of the Ru(II) cation [TpRu(PMe3)2(OH2)][OTf] is estimated to be between 82 and 85 kcal/mol, while computational studies yield a BDE of 84 kcal/mol, which are in reasonable agreement with the observed reactivity of [TpRu(PMe3)2OH]+.
Contributing Partner: UNT College of Arts and Sciences
Permallink:digital.library.unt.edu/ark:/67531/metadc77187/