Hydrogen Transfer in Polar Environments

This section turns to reactions involving the transfer of a proton in (primarily) polar environments, opening with a theoretical presentation and finishing with three experimental chapters all exploiting the greatly enhanced acidity of aromatic photoacids (compared to ground electronic state acids) in probing the details of proton transfer. 

11 by Lochbrunner, Schriever and Riedle deals with excited electronic state intramolecular tautomerization proton transfers in nonpolar, rather than polar, solvents. But there is a connection to the previous chapter the ultrafast optical experiments discussed here emphasize evidence that the proton is not the reaction coordinate. The proton transfer is controlled by low vibrational modes of the photo-acids, rather than by the proton motion itself, an interpretation supported by separate vibrational spectroscopic studies and theoretical calculations The key role of modes reducing the donor-acceptor distance for proton transfer is highlighted, and for the featured molecule of this chapter, the proton adiabatically follows the low frequency modes, and no tunneling or barrier for the proton occurs. (See also Ch. 15 by Elsaesser for direct ultrafast vibrational studies on these issues). 

Pines and Pines return to proton transfer in polar solvents and investigate the factors affecting the photoacidity of weak organic acids such as phenols 

Hydrogen-Transfer Reactions. Edited by J. T. Hynes, J. P. Klinman, H. H. Limbach, and R. L. Schowen Copyright 2007 WILEY-VCH Veriag GmbH Co. KGaA, Weinheim ISBN 978-3-527-30777-7 

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