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Articles 1 - 4 of 4
Full-Text Articles in Computational Chemistry
Contributions Of Tunneling In 8Π-6Π Electrocyclic Cascade Reactions Of Bicyclo[4.2.0]Octa-2,4-Diene Moieties, Ishika Jain, Claire Castro, William L. Karney
Contributions Of Tunneling In 8Π-6Π Electrocyclic Cascade Reactions Of Bicyclo[4.2.0]Octa-2,4-Diene Moieties, Ishika Jain, Claire Castro, William L. Karney
Featured Student Work
Six-electron electrocyclic reactions usually require relatively high temperatures; however recent research has shown that such reactions can occur at significantly lower temperatures in biosynthetic and biomimetic pathways. Pathways resulting in bicyclo[4.2.0]octa-2,4-diene moieties arise from thermally allowed 8π-6π electrocyclization cascade reactions of 1,3,5,7-octatetraenes, as in the biosynthesis of endiandric acids, elysiapyrones, and numerous other natural products. We report multidimensional tunneling calculations to explore the possible contribution of heavy-atom tunneling (e.g. by carbon) to biosynthetic pathways and biomimetic syntheses, and thus to provide a more complete picture of biochemical kinetics. M06-2X/cc-pVDZ calculations on the 8π-6π cascade cyclizations of methylated octatetraene model systems …
Additivity Of Diene Substituent Gibbs Free Energy Contributions For Diels–Alder Reactions Between Me2c=Cme2 And Substituted Cyclopentadienes, Thomas M. Gilbert, Austin S. Flemming, Brendan C. Dutmer
Additivity Of Diene Substituent Gibbs Free Energy Contributions For Diels–Alder Reactions Between Me2c=Cme2 And Substituted Cyclopentadienes, Thomas M. Gilbert, Austin S. Flemming, Brendan C. Dutmer
Faculty Peer-Reviewed Publications
Systematic computational studies of pericyclic Diels–Alder reactions between (H3C)2C═C(CH3)2, 1, and all permutations of substituted cyclopentadienes c-C5R1R2R3R4R5aR5b (R = H, CH3, CF3, F) allowed isolation of substitutional effects on Gibbs free energy barrier heights and reaction Gibbs free energies. “Average Substitution Gibbs Free Energy Correction” ΔGASC#‡/ΔGASC# values for each substituent in each position appeared to be additive. Substituent effects on barriers showed interesting contrasts. Methyl substitution at positions 5a and 5b increased barriers significantly, while substitution at all other positions had essentially no impact. In contrast, fluoro substitution at positions 5a and 5b lowered barriers more than substitution at other …
Solvation Of Large Polycyclic Aromatic Hydrocarbons In Helium: Cationic And Anionic Hexabenzocoronene, Miriam Kappe, Florent Calvo, Johannes Schöntag, Holger F. Bettinger, Serge Krasnokutski, Martin Kuhn, Elisabeth Gruber, Fabio Zappa, Paul Scheier, Olof E. Echt
Solvation Of Large Polycyclic Aromatic Hydrocarbons In Helium: Cationic And Anionic Hexabenzocoronene, Miriam Kappe, Florent Calvo, Johannes Schöntag, Holger F. Bettinger, Serge Krasnokutski, Martin Kuhn, Elisabeth Gruber, Fabio Zappa, Paul Scheier, Olof E. Echt
Faculty Publications
The adsorption of helium on charged hexabenzocoronene (Hbc, C42H18), a planar polycyclic aromatic hydrocarbon (PAH) molecule of D6h symmetry, is investigated by a combination of high-resolution mass spectrometry and classical and quantum computational methods. The ion abundance of HenHbc+ complexes versus size n features prominent local anomalies at n = 14, 38, 68, 82, and a weak one at 26, indicating that for these “magic” sizes the helium evaporation energies are relatively large. Surprisingly, mass spectra of anionic HenHbc– complexes feature a different set of anomalies, namely at …
Calcium Bistriflimide-Mediated Sulfur (Vi)–Fluoride Exchange (Sufex): Mechanistic Insights Toward Instigating Catalysis, Nicholas Ball, Brian Han, Samuel R. Khasnavis, Matthew Nwerem, Michael Bertagna, O Maduka Ogba
Calcium Bistriflimide-Mediated Sulfur (Vi)–Fluoride Exchange (Sufex): Mechanistic Insights Toward Instigating Catalysis, Nicholas Ball, Brian Han, Samuel R. Khasnavis, Matthew Nwerem, Michael Bertagna, O Maduka Ogba
Pomona Faculty Publications and Research
We report a mechanistic investigation of calcium bistriflimide-mediated sulfur(VI)–fluoride exchange (SuFEx) between sulfonyl fluorides and amines. We determine the likely pre-activation resting state─a calcium bistriflimide complex with ligated amines─thus allowing for corroborated calculation of the SuFEx activation barrier at ∼21 kcal/mol, compared to 21.5 ± 0.14 kcal/mol derived via kinetics experiments. Transition state analysis revealed: (1) a two-point calcium-substrate contact that activates the sulfur(VI) center and stabilizes the leaving fluoride and (2) a 1,4-diazabicyclo[2.2.2]octane additive that provides Brønsted-base activation of the nucleophilic amine. Stable Ca–F complexes upon sulfonamide formation are likely contributors to inhibited catalytic turnover, and a proof-of-principle redesign …