$^{a}$P. Botschwina, T. Dutoi, M. Mladenovi\'c, Rainer Oswald, S. Schmatz and H. Stoll, Farad... more $^{a}$P. Botschwina, T. Dutoi, M. Mladenovi\'c, Rainer Oswald, S. Schmatz and H. Stoll, Faraday Discuss., in press. $^{b}$P. Botschwina and H. Stoll, Phys. Chem. Chem. Phys., in press.
Physical chemistry chemical physics : PCCP, Jan 28, 2015
A nearside/farside analysis of differential cross sections has been performed for the complex-for... more A nearside/farside analysis of differential cross sections has been performed for the complex-forming SN2 reaction Cl(-) + CH3Br → ClCH3 + Br(-). It is shown that for low rotational quantum numbers a direct "nearside" reaction mechanism plays an important role and leads to anisotropic differential cross sections. For high rotational quantum numbers, indirect mechanisms via a long-lived intermediate complex are prevalent (independent of a nearside/farside configuration), leading to isotropic cross sections. Quantum mechanical interference can be significant at specific energies or angles. Averaging over energies and angles reveals that the nearside/farside decomposition in a semiclassical interpretation can reasonably account for the analysis of the reaction mechanism.
Large-scale calculations of accurate energy levels for the system in its electronic ground state ... more Large-scale calculations of accurate energy levels for the system in its electronic ground state are reported. The rovibrational levels are calculated for total angular momentum 1, and 2 by means of the discrete variable representation of the angular coordinate in conjunction ...
culated for a one year follow-up. Adherence was measured using proportion of days covered (PDC), ... more culated for a one year follow-up. Adherence was measured using proportion of days covered (PDC), where a PDCՆ80 was considered adherent. Multi-variable linear regression was used to examine the relationships between cost and adherence, controlling for patient demographics (age, gender, and job type) and Charlson comorbidity score. RESULTS: Among the 4978 individuals included in the study, the average adherence to oral hypoglycemic agents was 72.7%, and 56.6% (Nϭ2820) of the study population had a PDCՆ80. The mean total medical/pharmacy costs were similar for both the adherent and the non-adherent. Individuals who were adherent to their diabetes medications, however, had significantly lower shortterm disability costs ($1161/year) than did the non-adherent ($1840/year). CONCLUSIONS: In general, diabetes patients who adhered to their treatment regimen had much lower short-term disability costs when compared to the nonadherent. This result carries special implications for employers concerned with the total costs associated with diabetes in their employee populations.
Employing dimensionality-reduced time-independent quantum scattering theory and summation over al... more Employing dimensionality-reduced time-independent quantum scattering theory and summation over all possible total angular momentum states, initial-state selected reaction cross sections for the exothermic gas-phase bimolecular nucleophilic substitution (S N 2) reaction Cl À + CH 3 Br-ClCH 3 + Br À have been calculated. The carbon-halogen bonds and the rotation of the methyl halides are taken into account. In agreement with previous calculations for J = 0, initial rotational motion of CH 3 Br decreases the reaction probability and consequently the cross sections. The experimentally obtained thermal rate constant for 300 K is reproduced within the experimental error. For lower temperatures, it is calculated to be below the experimental values but shows the same strong increase for T-0.
The rovibrational (J = 0-4) level structure of protonated nitrogen (HNT) is investigated in detai... more The rovibrational (J = 0-4) level structure of protonated nitrogen (HNT) is investigated in detail for the CCSD (T) potential energy surface of Schmatz and Botschwina. The discrete variable representation (DVR) for the angular coordinate in conjunction with a distributed Gaussian basis set (DGB) for the radial degrees of freedom was used to perform the nuclear dynamics calculations. Both low lying and highly excited states are examined. The total number of bound states with J = 0 up to the first dissociation threshold at 44409 cm-' is determined to be about 5000. We propose an empirical model for the level structure of HN,f which incorporates Troe's suggestion for stretch-bend coupling. The empirical numbers and densities of states agree well with the corresponding numerically exact quantum mechanical values for the given surface.
Within the framework of reduced-dimensionality quantum scattering theory, we employ Bowman&am... more Within the framework of reduced-dimensionality quantum scattering theory, we employ Bowman's adiabatic rotation approximation to describe reactive systems that have symmetric-top geometries during the entire collision process. The results are compared with the approach of shifting the total energy by a characteristic rotational energy. Initial state-selected and total thermal rate constants have been computed for the complex-forming gas-phase reaction Cl(-) + CH(3)Cl' --> ClCH(3) + Cl'(-). At room temperature, we find a significant contribution from energetically high vibrational modes. The dependence of the cross-sections on the different angular momenta is analyzed in detail, and high total angular momenta are found to be of considerable importance. The influence of adiabatic azimuthal rotation on the rate constants turns out to be small compared to other effects. In addition, we use a new model to account for the asymmetric modes not explicitly contained in the scattering calculations. The difference to the only available experimental value confirms our conclusion that the Cl-C-Cl' bending modes are of major importance for this reaction.
Due to the easy migration of silyl groups, the chemistry of silylpyrazolones exhibits various uni... more Due to the easy migration of silyl groups, the chemistry of silylpyrazolones exhibits various unimolecular reaction channels not encountered in conventional pyrazolone chemistry. The unimolecular rearrangement process starting from the CH form of N-(trimethylsilyl)pyrazolone (which is primarily formed in the intramolecular condensation reaction of silylhydrazones) is investigated by density functional (B3LYP) and ab initio (MP2) calculations. The transition states are discussed in detail. First, the organosilyl group migrates from the nitrogen atom to the oxygen atom (1,3-Si shift). The second and third steps consist of two consecutive 1,2-H shifts from the carbon to the nitrogen atom. The barriers for the hydrogen migrations determine the overall classical barrier. In comparison to the reactant CH form, the most stable isomer O-silylpyrazolone is lower in energy by 5 kcal mol-1. This finding is in agreement with the experimental result. The calculated structure of this isomer is compared with X-ray diffraction data. The OH and NH forms of N-(trimethylsilyl)pyrazolone are slightly higher in energy than the CH form.
ABSTRACT Quantum mechanical cross-sections for the collinear SN2 reactions and have been calculat... more ABSTRACT Quantum mechanical cross-sections for the collinear SN2 reactions and have been calculated within the time-independent hyperspherical coordinate approach employing two-dimensional CCSD(T) potential energy surfaces. Compared to the results obtained from the potentials of Hase and co-workers, the recent cross-sections show several different features. However, the cross-sections calculated using the CCSD(T) potential energy surface for Cl−+CH3Br do not explain the experimentally observed independence of the rate constant on initial CH3Br temperature.
Employing a 4D CCSD(T) potential energy surface, initial-state selected reaction cross sections f... more Employing a 4D CCSD(T) potential energy surface, initial-state selected reaction cross sections for the complex-forming gas-phase identity S(N)2 reaction Cl(-) + CH3Cl' (v1, v2, v3) --> ClCH3 (v'1, v'2, v'3) + Cl'- havebeen calculated by means of time-independent quantum scattering theory in hyperspherical coordinates. The totally symmetric internal modes of the methyl group (C-H stretching vibration, quantum numbers v1 and v'1, and umbrella bending vibration, v2 and v'2) and the two C-Cl stretching modes (v3 and v'3) are included. The results for pure C-Cl stretching excitation in the reactants are similar to those obtained in earlier 2D calculations. The cooperative effect of C-Cl stretching and umbrella bending modes is even more pronounced for cross sections than for reaction probabilities. The same holds for excitations of the pure internal CH3 modes; in particular, the ratio of cross sections for reaction with the C-H stretch excited to reaction out of the vibrational ground state is five orders of magnitude larger than the ratio of the corresponding probabilities. This questions the concept of "spectator" modes in reaction dynamics which is valid only for thermal rate constants where the "spectator" modes play a negligible role due to their low population. Transition state theory rate constants fortuitously show good agreement with experiment while the reduced-dimensionality quantum calculations show larger deviations. Possible sources of this discrepancy are discussed in detail. Neglect of reactant CH3Cl rotation and the related modes in the transition state (doubly degenerate Cl-...CH3...Cl' bend and K rotation) yields very good agreement with experiment.
Summary: The debate on the mechanism of dithiobenzoate-mediated RAFT polymer-ization may be overc... more Summary: The debate on the mechanism of dithiobenzoate-mediated RAFT polymer-ization may be overcome by taking the so-called ''missing step'' reaction between a highly reactive propagating radical and the three-arm star-shaped product of the combination reaction of an ...
ABSTRACT The formation of the diazadisilacyclopentane 2 in a ring expansion reaction is the first... more ABSTRACT The formation of the diazadisilacyclopentane 2 in a ring expansion reaction is the first example of an SiR2CH2 insertion into the nitrogen−silicon single-bond accompanied by migration of a hydrogen atom from a carbon to a nitrogen atom [J. Organomet. Chem. 1994, 482, 285]. Density functional calculations support the experimental findings and suggest a reaction mechanism which includes two four-center transition states and an intermediate silahydrazone (3b). The reaction enthalpy ΔRH° (298 K) of the isomerization reaction converting the three-membered ring (Me3SiN)2SiH2 (1b) into the diazadisilacyclopentane Me2Si(NHNSiMe3CH2)SiH2 (2b) is calculated to be −23 kcal mol-1. Another intermediate of the system shows an unexpected electronic structure with a lone electron pair at the SiH2 silicon atom. The transition states and the unimolecular reaction mechanism are discussed in detail. The calculated geometry for the product 2b is in very good agreement with X-ray structure data.
ABSTRACT A new and effective organocatalytic system, primary amine derived chiral thiourea cataly... more ABSTRACT A new and effective organocatalytic system, primary amine derived chiral thiourea catalyst and AcOH/H2O additive, which converts different ketones to γ-nitroketones in high yields (82–99%) and enantioselectivities (90–99%) is described. The transition state geometries for formation of R and S enantiomers in this Michael addition have been calculated and analyzed. It is shown that only one oxygen atom of the nitro group is bound to the thiourea moiety, in juxtaposition to the literature-known working hypothesis which involves a bonding of both oxygens.
$^{a}$P. Botschwina, T. Dutoi, M. Mladenovi\'c, Rainer Oswald, S. Schmatz and H. Stoll, Farad... more $^{a}$P. Botschwina, T. Dutoi, M. Mladenovi\'c, Rainer Oswald, S. Schmatz and H. Stoll, Faraday Discuss., in press. $^{b}$P. Botschwina and H. Stoll, Phys. Chem. Chem. Phys., in press.
Physical chemistry chemical physics : PCCP, Jan 28, 2015
A nearside/farside analysis of differential cross sections has been performed for the complex-for... more A nearside/farside analysis of differential cross sections has been performed for the complex-forming SN2 reaction Cl(-) + CH3Br → ClCH3 + Br(-). It is shown that for low rotational quantum numbers a direct "nearside" reaction mechanism plays an important role and leads to anisotropic differential cross sections. For high rotational quantum numbers, indirect mechanisms via a long-lived intermediate complex are prevalent (independent of a nearside/farside configuration), leading to isotropic cross sections. Quantum mechanical interference can be significant at specific energies or angles. Averaging over energies and angles reveals that the nearside/farside decomposition in a semiclassical interpretation can reasonably account for the analysis of the reaction mechanism.
Large-scale calculations of accurate energy levels for the system in its electronic ground state ... more Large-scale calculations of accurate energy levels for the system in its electronic ground state are reported. The rovibrational levels are calculated for total angular momentum 1, and 2 by means of the discrete variable representation of the angular coordinate in conjunction ...
culated for a one year follow-up. Adherence was measured using proportion of days covered (PDC), ... more culated for a one year follow-up. Adherence was measured using proportion of days covered (PDC), where a PDCՆ80 was considered adherent. Multi-variable linear regression was used to examine the relationships between cost and adherence, controlling for patient demographics (age, gender, and job type) and Charlson comorbidity score. RESULTS: Among the 4978 individuals included in the study, the average adherence to oral hypoglycemic agents was 72.7%, and 56.6% (Nϭ2820) of the study population had a PDCՆ80. The mean total medical/pharmacy costs were similar for both the adherent and the non-adherent. Individuals who were adherent to their diabetes medications, however, had significantly lower shortterm disability costs ($1161/year) than did the non-adherent ($1840/year). CONCLUSIONS: In general, diabetes patients who adhered to their treatment regimen had much lower short-term disability costs when compared to the nonadherent. This result carries special implications for employers concerned with the total costs associated with diabetes in their employee populations.
Employing dimensionality-reduced time-independent quantum scattering theory and summation over al... more Employing dimensionality-reduced time-independent quantum scattering theory and summation over all possible total angular momentum states, initial-state selected reaction cross sections for the exothermic gas-phase bimolecular nucleophilic substitution (S N 2) reaction Cl À + CH 3 Br-ClCH 3 + Br À have been calculated. The carbon-halogen bonds and the rotation of the methyl halides are taken into account. In agreement with previous calculations for J = 0, initial rotational motion of CH 3 Br decreases the reaction probability and consequently the cross sections. The experimentally obtained thermal rate constant for 300 K is reproduced within the experimental error. For lower temperatures, it is calculated to be below the experimental values but shows the same strong increase for T-0.
The rovibrational (J = 0-4) level structure of protonated nitrogen (HNT) is investigated in detai... more The rovibrational (J = 0-4) level structure of protonated nitrogen (HNT) is investigated in detail for the CCSD (T) potential energy surface of Schmatz and Botschwina. The discrete variable representation (DVR) for the angular coordinate in conjunction with a distributed Gaussian basis set (DGB) for the radial degrees of freedom was used to perform the nuclear dynamics calculations. Both low lying and highly excited states are examined. The total number of bound states with J = 0 up to the first dissociation threshold at 44409 cm-' is determined to be about 5000. We propose an empirical model for the level structure of HN,f which incorporates Troe's suggestion for stretch-bend coupling. The empirical numbers and densities of states agree well with the corresponding numerically exact quantum mechanical values for the given surface.
Within the framework of reduced-dimensionality quantum scattering theory, we employ Bowman&am... more Within the framework of reduced-dimensionality quantum scattering theory, we employ Bowman's adiabatic rotation approximation to describe reactive systems that have symmetric-top geometries during the entire collision process. The results are compared with the approach of shifting the total energy by a characteristic rotational energy. Initial state-selected and total thermal rate constants have been computed for the complex-forming gas-phase reaction Cl(-) + CH(3)Cl' --> ClCH(3) + Cl'(-). At room temperature, we find a significant contribution from energetically high vibrational modes. The dependence of the cross-sections on the different angular momenta is analyzed in detail, and high total angular momenta are found to be of considerable importance. The influence of adiabatic azimuthal rotation on the rate constants turns out to be small compared to other effects. In addition, we use a new model to account for the asymmetric modes not explicitly contained in the scattering calculations. The difference to the only available experimental value confirms our conclusion that the Cl-C-Cl' bending modes are of major importance for this reaction.
Due to the easy migration of silyl groups, the chemistry of silylpyrazolones exhibits various uni... more Due to the easy migration of silyl groups, the chemistry of silylpyrazolones exhibits various unimolecular reaction channels not encountered in conventional pyrazolone chemistry. The unimolecular rearrangement process starting from the CH form of N-(trimethylsilyl)pyrazolone (which is primarily formed in the intramolecular condensation reaction of silylhydrazones) is investigated by density functional (B3LYP) and ab initio (MP2) calculations. The transition states are discussed in detail. First, the organosilyl group migrates from the nitrogen atom to the oxygen atom (1,3-Si shift). The second and third steps consist of two consecutive 1,2-H shifts from the carbon to the nitrogen atom. The barriers for the hydrogen migrations determine the overall classical barrier. In comparison to the reactant CH form, the most stable isomer O-silylpyrazolone is lower in energy by 5 kcal mol-1. This finding is in agreement with the experimental result. The calculated structure of this isomer is compared with X-ray diffraction data. The OH and NH forms of N-(trimethylsilyl)pyrazolone are slightly higher in energy than the CH form.
ABSTRACT Quantum mechanical cross-sections for the collinear SN2 reactions and have been calculat... more ABSTRACT Quantum mechanical cross-sections for the collinear SN2 reactions and have been calculated within the time-independent hyperspherical coordinate approach employing two-dimensional CCSD(T) potential energy surfaces. Compared to the results obtained from the potentials of Hase and co-workers, the recent cross-sections show several different features. However, the cross-sections calculated using the CCSD(T) potential energy surface for Cl−+CH3Br do not explain the experimentally observed independence of the rate constant on initial CH3Br temperature.
Employing a 4D CCSD(T) potential energy surface, initial-state selected reaction cross sections f... more Employing a 4D CCSD(T) potential energy surface, initial-state selected reaction cross sections for the complex-forming gas-phase identity S(N)2 reaction Cl(-) + CH3Cl' (v1, v2, v3) --> ClCH3 (v'1, v'2, v'3) + Cl'- havebeen calculated by means of time-independent quantum scattering theory in hyperspherical coordinates. The totally symmetric internal modes of the methyl group (C-H stretching vibration, quantum numbers v1 and v'1, and umbrella bending vibration, v2 and v'2) and the two C-Cl stretching modes (v3 and v'3) are included. The results for pure C-Cl stretching excitation in the reactants are similar to those obtained in earlier 2D calculations. The cooperative effect of C-Cl stretching and umbrella bending modes is even more pronounced for cross sections than for reaction probabilities. The same holds for excitations of the pure internal CH3 modes; in particular, the ratio of cross sections for reaction with the C-H stretch excited to reaction out of the vibrational ground state is five orders of magnitude larger than the ratio of the corresponding probabilities. This questions the concept of "spectator" modes in reaction dynamics which is valid only for thermal rate constants where the "spectator" modes play a negligible role due to their low population. Transition state theory rate constants fortuitously show good agreement with experiment while the reduced-dimensionality quantum calculations show larger deviations. Possible sources of this discrepancy are discussed in detail. Neglect of reactant CH3Cl rotation and the related modes in the transition state (doubly degenerate Cl-...CH3...Cl' bend and K rotation) yields very good agreement with experiment.
Summary: The debate on the mechanism of dithiobenzoate-mediated RAFT polymer-ization may be overc... more Summary: The debate on the mechanism of dithiobenzoate-mediated RAFT polymer-ization may be overcome by taking the so-called ''missing step'' reaction between a highly reactive propagating radical and the three-arm star-shaped product of the combination reaction of an ...
ABSTRACT The formation of the diazadisilacyclopentane 2 in a ring expansion reaction is the first... more ABSTRACT The formation of the diazadisilacyclopentane 2 in a ring expansion reaction is the first example of an SiR2CH2 insertion into the nitrogen−silicon single-bond accompanied by migration of a hydrogen atom from a carbon to a nitrogen atom [J. Organomet. Chem. 1994, 482, 285]. Density functional calculations support the experimental findings and suggest a reaction mechanism which includes two four-center transition states and an intermediate silahydrazone (3b). The reaction enthalpy ΔRH° (298 K) of the isomerization reaction converting the three-membered ring (Me3SiN)2SiH2 (1b) into the diazadisilacyclopentane Me2Si(NHNSiMe3CH2)SiH2 (2b) is calculated to be −23 kcal mol-1. Another intermediate of the system shows an unexpected electronic structure with a lone electron pair at the SiH2 silicon atom. The transition states and the unimolecular reaction mechanism are discussed in detail. The calculated geometry for the product 2b is in very good agreement with X-ray structure data.
ABSTRACT A new and effective organocatalytic system, primary amine derived chiral thiourea cataly... more ABSTRACT A new and effective organocatalytic system, primary amine derived chiral thiourea catalyst and AcOH/H2O additive, which converts different ketones to γ-nitroketones in high yields (82–99%) and enantioselectivities (90–99%) is described. The transition state geometries for formation of R and S enantiomers in this Michael addition have been calculated and analyzed. It is shown that only one oxygen atom of the nitro group is bound to the thiourea moiety, in juxtaposition to the literature-known working hypothesis which involves a bonding of both oxygens.
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Papers by Stefan Schmatz