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Journals and Conferences
Equilibria for the reactions of benzhydryl cations (Ar2CH(+)) with phosphines, tert-amines, pyridines, and related Lewis bases were determined photometrically in CH2Cl2 and CH3CN solution at 20 °C. The measured equilibrium constants can be expressed by the sum of two parameters, defined as the Lewis Acidity (LA) of the benzhydrylium ions and the Lewis… (More)
The nucleophilicity parameters N and sN, as defined by the linear free-energy equation logk(20 °C)= sN(N+ E), of the 2imidazolines 1a–d and the related N-heterocyclic compounds 2–5 have been determined by studying the rates of their reactions with differently substituted benzhydrylium ions in dichloromethane at 20 °C by stopped-flow or laser flash… (More)
The key steps in most organocatalytic cyclizations are the reactions of electrophiles with nucleophiles. Their rates can be calculated by the linear free-energy relationship log k(20 °C) = s(N)(E + N), where electrophiles are characterized by one parameter (E) and nucleophiles are characterized by the solvent-dependent nucleophilicity (N) and sensitivity… (More)
Selective functionalization of ubiquitous C(sp3)-H bonds using visible light is a highly challenging yet desirable goal in organic synthesis. The development of such processes relies on both rational design and serendipitous discoveries from innovative tools such as screening technologies. Applying a mechanism-based screening strategy, we herein report… (More)
Oxygen versus carbon: Azolium enolates were generated by the reactions of N-heterocyclic carbenes (NHCs) with methyl phenyl ketene and characterized by X-ray crystallography. Kinetic studies show that the enolate oxygen is 20 times more nucleophilic than the carbon atom, but under thermodynamic control exclusive C-addition products were formed.
Rate and equilibrium constants for the reactions of a series of isothioureas with benzhydrylium ions have been measured photometrically. The data were employed to determine the nucleophilicities and nucleofugalities of isothioureas and compare them with those of other organocatalysts.
Dedicated to Professor Heinrich Nöth on the occasion of his 85th birthday The nucleophile-specific parameters N and sN, as defined by the linear free energy relationship log k = sN(N +E) (J. Am. Chem. Soc. 2001, 123, 9500 – 9512), were determined for five imines 1a–e by studying the kinetics of their reactions with benzhydrylium ions in dichloromethane… (More)
The kinetics of the reactions of thiocarboxylate and thiocarbonate anions with benzhydrylium ions have been determined in acetonitrile solution using laser-flash photolytic techniques. The second-order rate constants (k) correlate linearly with the electrophilicity parameters E of the benzhydrylium ions, as required by the correlation log k (20 °C) = s(N)(N… (More)