The free radical chlorination of alkanes was examined in several solvents. The results of these experiments suggest that Cl• forms complexes with halogenated solvents and that these complexes exhibit higher selectivity in hydrogen abstractions than "free" chlorine atom. The observed selectivity decreases with increasing Cl-content of the solvent (paralleling the increase in the ionization potential of the solvent), and selectivity is greater in bromoalkane solvents compared to chloroalkanes, suggesting that these are donor/acceptor-type complexes.
The chlorine atom cage effect was used as a highly sensitive probe for studying the effect of viscosity
and the possible role of solvent clusters on cage lifetimes and reactivity for reactions carried out in supercritical
fluid solvents. These experiments were conducted in supercritical carbon dioxide (SC-CO2, 40 °C, at various
pressures) with parallel experiments in conventional solvents and in the gas phase. The results of these
experiments provide no indication of an enhanced cage effect near the critical point in SC-CO2 solvent. The
magnitude of the cage effect observed in SC-CO2 at all pressures examined is well within what is anticipated
on the basis of extrapolations from conventional solvents.
Photoacoustic calorimetry (PAC) is a powerful tool for studying photophysical properties of molecules and energetics of discrete chemical reactions. PAC can be thought of simply as "listening to molecules" as they decay from an energetically excited state. The laser technology employed is similar to that already used in many physical chemistry laboratories and is therefore easily implemented as a complementary exercise to existing laser experiments. Two projects illustrate PAC as applied to two different chemical systems while utilizing identical theory, equipment, and procedure. Numerous other chemical systems are also addressable by this state-of-the-art technology.
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