Electronic states of azabenzenes: A critical review

Interpretation of the ultraviolet spectral changes of proteins.

Synthesis and chemistry of acyl silanes

Es wird eine Ubersicht uber die in den letzten Jahren ermittelten empirischen Parameter der Losungsmittelpolaritat gegeben: Y-Werte (Winstein, Grunwald), X-Werte (Gielen, Nasielski), Ω-Werte (Berson, Hamlet, Mueller), Z-Werte (Kosower), ET-Werte (Dimroth, Reichardt, Siepmann, Bohlmann), R- und S-Werte (Brownstein). Ihr Anwendungsbereich und ihre Korrelationen untereinander werden diskutiert. — Die theoretischen Grundlagen des Losungsmitteleinflusses auf Reaktionsgeschwindigkeit und Lichtabsorption organischer Verbindungen werden kurz erlautert und Versuche erwahnt, physikalische Kennzahlen der Losungsmittel mit den empirischen Parametern in Beziehung zu bringen.

Empirische Parameter der Lösungsmittelpolarität

In order to clarify mechanisms of excited state interactions in hydrogen-bonded pairs, we have studied the kinetics of dynamic quenching of singlet and triplet fluorenone by a series of alcohols, phenols, and related compounds, in which hydrogen-bonding power, redox potential, and acidity are systematically varied. In addition, effects of solvent basicity or polarity and deuteration help identify the role of hydrogen-bonding in physical or chemical quenching processes. Alcohols and weak acids, with high oxidation potentials, do not quench the triplet, but quench the singlet at rates which parallel hydrogen-bonding power. This is attributed to a physical mechanism, involving vibronic coupling to the ground state via the hydrogen bond. This is much stronger in the excited state than in the ground state, and provides efficient energy dissipation in the radiationless transition. Phenols, with hydrogen-bonding power comparable to that of the alcohols but with much lower oxidation potentials, quench both single...

Graham J. Brealey

Papers

The Rôle of Hydrogen Bonding in the n → π* Blue-shift Phenomenon1