Y. Okamoto

Bio: Y. Okamoto is an academic researcher. The author has contributed to research in topics: Solvolysis & Steric effects. The author has an hindex of 11, co-authored 13 publications receiving 1503 citations.

Predicting the activity of phenolic antioxidants: theoretical method, analysis of substituent effects, and application to major families of antioxidants.

Abstract: A procedure based on density functional theory is used for the calculation of the gas-phase bond dissociation enthalpy (BDE) and ionization potential for molecules belonging to the class of phenolic antioxidants. We show that use of locally dense basis sets (LDBS) vs full basis sets gives very similar results for monosubstituted phenols, and that the LDBS procedure gives good agreement with the change in experimental BDE values for highly substituted phenols in benzene solvent. Procedures for estimating the O--H BDE based on group additivity rules are given and tested. Several interesting classes of phenolic antioxidants are studied with these methods, including commercial antioxidants used as food additives, compounds related to Vitamin E, flavonoids in tea, aminophenols, stilbenes related to resveratrol, and sterically hindered phenols. On the basis of these results we are able to interpret relative rates for the reaction of antioxidants with free radicals, including a comparison of both H-atom-transfer and single-electron-transfer mechanisms, and conclude that in most cases H-atom transfer will be dominant.

Mechanistic Aspects of Diels‐Alder Reactions: A Critical Survey

Abstract: The question of concerted or consecutive bond formation arises in all types of cycloaddition reactions. Stereochemical investigations and studies of regiospecificity as well as intensive kinetic investigations with regard to substituent and solvent effects, and the dependence of the reaction on temperature and pressure permit in many cases mechanistic conclusions concerning the Diels-Alder reaction. Efforts towards a theoretical interpretation, ab initio and semiempirical calculations, the application of frontier molecular orbital theory (FMO) as well as thermochemical measurements permit a description of the energy hypersurface of these [4+2]-cycloadditions. An attempt is made here to draw a line of distinction between the mechanistic alternatives—one-step reaction versus two-step reaction—considering all experimental and theoretical criteria.

Oxide Defect Engineering Enables to Couple Solar Energy into Oxygen Activation

Abstract: Modern development of chemical manufacturing requires a substantial reduction in energy consumption and catalyst cost. Sunlight-driven chemical transformation by metal oxides holds great promise for this goal; however, it remains a grand challenge to efficiently couple solar energy into many catalytic reactions. Here we report that defect engineering on oxide catalyst can serve as a versatile approach to bridge light harvesting with surface reactions by ensuring species chemisorption. The chemisorption not only spatially enables the transfer of photoexcited electrons to reaction species, but also alters the form of active species to lower the photon energy requirement for reactions. In a proof of concept, oxygen molecules are activated into superoxide radicals on defect-rich tungsten oxide through visible-near-infrared illumination to trigger organic aerobic couplings of amines to corresponding imines. The excellent efficiency and durability for such a highly important process in chemical transformation can otherwise be virtually impossible to attain by counterpart materials.

1.3-Dipolare Cycloadditionen, XXXII. Kinetik der Additionen organischer Azide an CC-Mehrfachbindungen

Abstract: Die IR-spektrophotometrisch gemessenen Additionskonstanten des Phenylazids an 27 olefinische und 4 acetylenische Dipolarophile bei 25° liegen im Bereich von 7 Zehnerpotenzen; das Zusammenspiel elektronischer und sterischer Substituenteneffekte beim Dipolarophil wird diskutiert. — Kernsubstituierte Phenylazide befolgen in ihren Additionsgeschwindigkeiten die Hammett-Gleichung, wobei der ρ-Wert vom Dipolarophil abhangt: Maleinsaureanhydrid −1.1, N-Phenyl-maleinimid −0.8, Norbornen +0.88, Cyclopenten +0.9, 1-Pyrrolidino-cyclohexen +2.5. − Die fur vier Azid-Cycloadditionen ermittelten Aktivierungsentropien betragen −26 bis −36 Clausius. Die Additionskonstante des Phenylazids an Pyrrolidino-cyclopenten hangt nur wenig von der Solvenspolaritat ab. All diese Daten weisen auf eine Mehrzentren-Cycloaddition der organischen Azide.