Steric Demand and Rate-determining Step for Photoenolization of Di-ortho-substituted Acetophenone Derivatives

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dc.contributor.authorDas, Anushree
dc.contributor.authorThomas, Suma S.
dc.contributor.authorGarofoli, August A.
dc.contributor.authorChavez, Kevin A.
dc.contributor.authorKrause, Jeanette A.
dc.contributor.authorBohne, Cornelia
dc.contributor.authorGudmundsdottir, Anna D.
dc.date.accessioned2020-08-14T19:01:50Z
dc.date.available2020-08-14T19:01:50Z
dc.date.copyright2018en_US
dc.date.issued2018
dc.description.abstractLaser flash photolysis of ketone 1 in argon‐saturated methanol yields triplet biradical 1BR (τ = 63 ns) that intersystem crosses to form photoenols Z‐1P (λ max = 350 nm, τ ~ 10 μs) and E‐1P (λ max = 350 nm, τ > 6 ms). The activation barrier for Z‐1P re‐forming ketone 1 through a 1,5‐H shift was determined as 7.7 ± 0.3 kcal mol−1. In contrast, for ketone 2, which has a less sterically hindered carbonyl moiety, laser flash photolysis in argon‐saturated methanol revealed the formation of biradical 2BR (λ max = 330 nm, τ ~ 303 ns) that intersystem crosses to form photoenol E‐2P (λ max = 350 nm, τ > 42 μs), but photoenol Z‐2P was not detected. However, in more viscous basic H‐bond acceptor (BHA ) solvent, such as hexamethylphosphoramide, triplet 2BR intersystem crosses to form both Z‐2P (λ max = 370 nm, τ ~ 1.5 μs) and E‐2P. Thus, laser flash photolysis of ketone 2 in methanol reveals that intersystem crossing from 2BR to form Z‐2P is slower than the 1,5‐H shift of Z‐2P, whereas in viscous BHA solvents, the 1,5‐H shift becomes slower than the intersystem crossing from 2BR to Z‐2P. Density functional theory and coupled cluster calculations were performed to support the reaction mechanisms for photoenolization of ketones 1 and 2 .en_US
dc.description.reviewstatusRevieweden_US
dc.description.scholarlevelFacultyen_US
dc.description.sponsorshipWe acknowledge funding from NSF (CHE‐1464694) and the Ohio Supercomputer Center for supporting this work. AD is grateful for generous support from the Chemistry Department at the University of Cincinnati including a RITE fellowship. Researchers at UVic thank NSERC (RGPIN‐121389‐2012) for funding and CAMTEC for the use of shared facilities.en_US
dc.identifier.citationDas, A., Thomas, S. S., Garofoli, A. A., Chavez, K. A., Krause, J. A., Bohne, C., & Gudmundsdottir, A. D. (2018). Steric Demand and Rate-determining Step for Photoenolization of Di-ortho-substituted Acetophenone Derivatives. Photochemistry and Photobiology, 95(1), 154-162. https://doi.org/10.1111/php.12996.en_US
dc.identifier.urihttps://doi.org/10.1111/php.12996
dc.identifier.urihttp://hdl.handle.net/1828/11993
dc.language.isoenen_US
dc.publisherPhotochemistry & Photobiologyen_US
dc.subjectCentre for Advanced Materials and Related Technology (CAMTEC)
dc.subject.departmentDepartment of Chemistry
dc.titleSteric Demand and Rate-determining Step for Photoenolization of Di-ortho-substituted Acetophenone Derivativesen_US
dc.typePostprinten_US

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