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Moose Jaw, Canada

Rayne S.,Chemologica Research | Forest K.,Saskatchewan Polytechnic
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2016

In order to estimate isomer-specific acidity constants (pKa) for the perfluorinated sulfonic acid (PFSA) environmental contaminants, the parameterization method 6 (PM6) pKa prediction method was extensively validated against a wide range of carbon oxyacids and related sulfonic/sulfinic acids. Excellent pKa prediction performance was observed for the carbon oxyacids using the PM6 method, but this approach was found to have a severe positive bias for sulfonic/sulfinic acids. To overcome this obstacle, a correlation was developed between non-adjusted PM6 pKa values and the corresponding experimentally obtained/estimated acidity constants for a range of representative alkyl, aryl and halogen-substituted sulfonic acids. Application of this correction to the PM6 values allows for extension of this computational method to a new acid functional group. When used to estimate isomer-specific pKa values for the C1 through C8 PFSAs, the modified PM6 approach suggests an adjusted pKa range from −5.3 to −9.0, indicating that all members of this class of well-known environmental contaminants will be effectively completely dissociated in aquatic systems. © 2016 Taylor & Francis Group, LLC Source

Rayne S.,Chemologica Research | Forest K.,Saskatchewan Polytechnic
Computational and Theoretical Chemistry | Year: 2016

Gas phase standard state (298.15K, 1atm) enthalpies of formation (δfH°(g)), enthalpies of disproportionation to two corresponding acetylene molecules (δrxnH°(g),Td→acet), and enthalpies of isomerization from a tetrahedrane geometry to a 1,3-cyclobutadiene structure (δisomH°(g),Td→CBD) were calculated for the mono- through tetra-substituted hydro, fluoro, chloro, bromo, methyl, ethynyl, and cyano carbon tetrahedrane derivatives at the G4(MP2) and G4 levels of theory. All derivatives have endothermic δfH°(g) indicative of the cage strain in these systems. In all cases, δrxnH°(g),Td→acet and δisomH°(g),Td→CBD are predicted to be substantially exothermic. High quality linear regression fits within a homologous series were obtained between the number of substituents and the G4(MP2)/G4 estimated δfH°(g). Via calculations on lower homolog members, this strategy was employed to allow extrapolated G4 and/or G4(MP2) δfH°(g) (as well as some δrxnH°(g),Td→acet and δisomH°(g),Td→CBD) to be obtained for the higher homolog t-butyl, trifluoromethyl, and trimethylsilyl carbon tetrahedrane derivatives. © 2015 Elsevier B.V. Source

Rayne S.,Chemologica Research | Forest K.,Saskatchewan Institute of Applied Science and Technology
Computational and Theoretical Chemistry | Year: 2011

Singlet-triplet (S0→T1) well-to-well (WWES-T) and vertical (VES-T) excitation energies of the [4×n] rectangular graphene nanoribbon series (n=2-6) were estimated using various semiempirical, Hartree-Fock (HF), density functional (DFT), and second order Moller-Plesset perturbation theory methods with the assumption of a closed-shell singlet state. Significant model chemistry dependent variability in theoretically obtained WWES-T/VES-T is evident for the rectangular graphene nanoribbons. With the exception of the B2PLYP density functional (which, along with the mPW2PLYP functional, combines exact HF exchange with an MP2-like correlation to the DFT calculation), all DFT, semiempirical, and HF methods investigated predict the onset of a negative WWES-T/VES-T (ground state triplet) starting somewhere between the [4×3] through [4×6] derivatives, with most functionals predicting a transition from a singlet to triplet ground state between the [4×4] and [4×5] rectangular graphene nanoribbons. Consistent with previous work on the n-acene series, MP2 WWES-T/VES-T estimates have a significant positive systematic bias and HF estimates have substantial negative systematic biases. Extrapolation of the B2PLYP results, which are in excellent agreement with prior FPA-QZ VES-T estimates, for any [m×n] rectangular graphene nanoribbon derivatives predicts a vanishingly small singlet-triplet gap at the polymeric limit (m→∞ and/or n→∞). © 2011 Elsevier B.V. Source

Rayne S.,Chemologica Research | Forest K.,Saskatchewan Institute of Applied Science and Technology
Journal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering | Year: 2014

A high-level gas and aqueous phase theoretical thermodynamic study was conducted on the primary and related chemical reactions which occur during chloramination for water treatment using the G4MP2, G4, and W1BD composite methods with the SMD, PCM, and CPCM solvation models. The standard state (298.15 K, 1 atm or 1M) formation of mono-, di-, and tri-chloramines from their precursors via hypochlorous acid chlorination is substantially exothermic and exergonic in both the gas and aqueous phases. The excellent agreement between experimental and theoretical values for a range of structural and thermodynamic calculations on a suite of calibration compounds suggests that the G4MP2, G4, and W1BD calculations meet or exceed criteria for thermochemical accuracy. The temperature influence on the thermodynamics of chloramine formation is projected to be negligible regardless of phase between 0 and 100°C. Additional thermodynamic calculations were undertaken on associated chloramination reactions involving the disproportionation of monochloramine, the decomposition of di- and tri-chloramine, and the reactions of trichloramine with ammonia and dichloramine. The results from these investigations not only provide a better understanding of the reaction thermodynamics, they also allow for a more rigorous interpretation of proposed chloramination mechanisms. © 2014 Copyright Taylor & Francis Group, LLC. Source

Rayne S.,Chemologica Research | Forest K.,Saskatchewan Institute of Applied Science and Technology
Computational and Theoretical Chemistry | Year: 2012

Singlet-triplet excitation energies (E S-T) were calculated for the phenyl, 1-naphthyl, and 2-naphthyl cations using a broad range of model chemistries, including semiempirical, Hartree-Fock, density functional, Moller-Plesset perturbation, composite, coupled cluster, and quadratic configuration interaction methods and various basis sets. Substantial model chemistry dependent E S-T results were obtained for all three cations with correspondingly minimal basis set size effects. G4/G4MP2 composite method well-to-well (and adiabatic) E S-T for the phenyl, 1-naphthyl, and 2-naphthyl cations are 101.9/102.3 (101.7/102.0), 20.4/18.8 (19.3/17.8), and 21.6/21.4 (20.8/20.7)kJ/mol, respectively. All composite methods predict a substantially positive E S-T for the 1- and 2-naphthyl cations, and are in both quantitative and qualitative disagreement with many other model chemistries (particularly density functionals such as B3LYP) in estimating both the magnitude and sign of the singlet-triplet excitation energy for the 1- and 2-naphthyl cations. Composite method approaches suggest both the 1- and 2-naphthyl cations are ground state singlets with sufficiently large E S-T such that the population of the corresponding triplet state should be negligible, and thereby non-observable, where experimental conditions operate under thermodynamic control. © 2012 Elsevier B.V.. Source

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