@article{RagyanszkiFiserLeeRuffetal., author = {Ragyanszki, Anita and Fiser, Bela and Lee-Ruff, Edward and Liebman, Joel F.}, title = {Strained Small Nitrogen Heterocycles-Azabicyclobutanes and Azirines}, series = {ChemistrySelect}, volume = {8}, journal = {ChemistrySelect}, number = {26}, doi = {10.1002/slct.202301405}, pages = {e202301405}, abstract = {Small ring nitrogen heterocycles, azabicyclobutanes and azirines, were investigated by computational methods in order to address the discrepancy between their regioisomers 1- and 2-azabicyclobutane and 1H- and 2H-azirines. Both 1-azabicyclobutane and 2H-azirine are well known synthetic starting points to larger nitrogen heterocycles whereas 2-azabicyclobutane and 1H-azirine and their derivatives have yet to be reported as isolable compounds. Calculated parameters such as structure, base strength (proton affinities), NICS values and enthalpies of formation from which strain energies are derived are reported. The destabilization of the less stable regioisomers is attributed to homoantiaromaticity in 2-azabicyclobutane and antiaromaticity in 1H-azirine. Two stereoisomers exist for 2-azabicyclobutane with the endo- stereoisomer being more stable. This phenomenon is indicative of the hydrogen bond acceptor properties of the neighboring cyclpropane and the π-bond character of the central bond in 2-azabicyclobutane.}, language = {en} } @article{RozsaRagyanszkiViskolczetal., author = {Rozsa, Zsofia Borbala and Ragyanszki, Anita and Viskolcz, Bela and Szori, Milan}, title = {Chemical space of the singlet C4H8O2 species. A systematic theoretical analysis on their structural and thermochemical properties}, series = {Computational and Theoretical Chemistry}, volume = {1225}, journal = {Computational and Theoretical Chemistry}, doi = {10.1016/j.comptc.2023.114162}, pages = {114162}, abstract = {The goal of this study was to explore and define the thermodynamic properties of one of the subspaces of 'chemical space' using a mixture of graph theory and theoretical chemistry tools. Therefore, all possible mo- lecular structures with C4H8O2 stoichiometry were generated, considering constitutional isomers and molecular complexes. The thermodynamic properties of the obtained isomers have been obtained by G3MP2B3 protocol. The classification of the obtained isomers was simplified by using thermodynamic maps, which is an effective method for the comparison of thermodynamic stability for entities of complex molecular systems. Modern computational methods can be used to understand larger systems, which has made it possible to characterize a chemical subspace not only by selecting individual entities, but also as a whole. With this pro- cedure one can catch a glimpse into the diversity of a molecular system and predict further uses of newly discovered molecules or design molecules with predefined properties.}, language = {en} } @article{JuhaszSerraLakatosetal., author = {Juhasz, Anett and Serra, Uneri Haymana and Lakatos, Csilla and Vadkerti, Bence and Ragyanszki, Anita and Farkas, Odon and Keki, Sandor and Nagy, Lajos}, title = {The kinetics of uncatalyzed and catalyzed urethane forming reactions of aliphatic diisocyanates with butan-1-ol}, series = {New J. Chem.}, volume = {47}, journal = {New J. Chem.}, doi = {10.1039/d3nj02747c}, pages = {16096 -- 16107}, abstract = {The kinetics of the urethane forming reactions of hexamethylene diisocyanate (HDI), 4,4′-dicyclohexyl-methane-diisocyanate (HMDI) and isophorone diisocyanate (IPDI) with butan-1-ol were systematically studied by electrospray ionization mass spectrometry (ESI-MS) in the off-line mode. The reactions were performed in toluene solution in the temperature range of 50-80 °C and perdeuterated butan-1-ol was used for quenching the reaction. The butan-1-ol was employed in high excess to diisocyanates to obtain pseudo first-order rate coefficients. For rendering the kinetics, a simple A → B → C consecutive model was applied and found to adequately describe the observed kinetic behaviors. The corresponding rate coefficients were determined and reactivities of the diisocyanates were found to decrease in the order HDI > IPDI > HMDI. Furthermore, it was observed that the second isocyanate group in HDI, due to the ring formation by intramolecular hydrogen bonds, reacted faster with butan-1-ol after the first isocyanate moiety had reacted. The formation of hydrogen bonding rings was also confirmed by DFT calculations. However, the reactivity of the second isocyanate moiety (after the first one has reacted) did not change significantly in the case of HMDI. From the temperature dependences the apparent activation parameters such as the pre-exponential factors and activation energies were determined. In addition, the reactions were also studied at 80 °C in the presence of tin(II)-2-ethylhexanoate at different concentrations and a mechanism was proposed for the catalytic process.}, language = {en} } @article{JiRagyanszkiFournier, author = {Ji, Hongchen and Ragyanszki, Anita and Fournier, Rene A.}, title = {Machine learning estimation of reaction energy barriers}, series = {Computational and Theoretical Chemistry}, volume = {1229}, journal = {Computational and Theoretical Chemistry}, doi = {10.1016/j.comptc.2023.114332}, pages = {114332}, abstract = {We describe a machine learning approach to approximate reaction energy barriers (E), requiring as input only estimates of geometry and energies of reactants and products. Using the dataset of Grambow, Pattanaik, and Green [Sci. Data 7 (1 3 7) (2020)] for reactions involving seven or fewer non-hydrogen atoms, 300 reaction features are computed, and an estimate of E is obtained by fitting a Kernel Ridge Regression (KRR) model with Laplacian kernel to a subset of Density Functional Theory reaction barriers. Our main interest is small energy barriers with the goal of modeling reactions in the interstellar medium and circumstellar envelope. We omitted reactions with E > 40 kcal mol-1 to obtain a subset of 5,276 reactions for 5-fold cross-validation. For this set, the KRR model predicts E with a mean absolute error of 4.13 kcal mol-1 and a root-mean square error of 6.02 kcal mol-1.}, language = {en} } @article{KoyanagiLamboRagyanszkietal., author = {Koyanagi, Gregory K. and Lambo, Ricardo Lewis and Ragyanszki, Anita and Fournier, Rene A. and Horbatsch, Marko W. and Hessels, Eric A.}, title = {Accurate calculation of the interaction of a barium monofluoride molecule with an argon atom: A step towards using matrix isolation of BaF for determining the electron electric dipole moment}, series = {Journal of Molecular Spectroscopy}, volume = {391}, journal = {Journal of Molecular Spectroscopy}, doi = {10.1016/j.jms.2023.111736}, pages = {111736}, language = {en} } @article{LamboKoyanagiRagyanszkietal., author = {Lambo, Ricardo Lewis and Koyanagi, Gregory K. and Ragyanszki, Anita and Horbatsch, Marko and Fournier, Rene and Hessels, Eric A.}, title = {Calculation of the local environment of a barium monofluoride molecule in an argon matrix: a step towards using matrix-isolated BaF for determining the electron electric dipole moment}, series = {Molecular Physics}, volume = {121}, journal = {Molecular Physics}, number = {6}, doi = {10.1080/00268976.2023.2198044}, language = {en} }