RESUMO
The rate constant for the ß-scission of the cumyloxyl radical (kß) was measured in the presence of various added electrolytes in acetonitrile and DMSO solvent. The results show that in CH3CN, kß increases in the presence of added electrolyte, roughly paralleling the size of the cation: Li+ > Mg2+ ≈ Na+ > nBu4N+ > no added electrolyte. As suggested by Bietti et al. earlier, this effect is attributable to stabilizing ion-dipole interactions in the transition state of the developing carbonyl group, a conclusion further amplified by MO calculations (gas phase) reported herein. Compared to the gas phase predictions, however, this effect is seriously attenuated in solution because complexation of the cation to the electrophilic alkoxyl radical (relative to the solvent, CH3CN) is very weak. Because the interaction of Li+ and Na+ is much stronger with DMSO than with CH3CN, addition of these ions has no effect on the rate of ß-scission.
RESUMO
When female birds lay eggs, some of their body burden of mercury is eliminated into each egg, potentially leading to declining mercury across the clutch. However, there was no decline in mercury with laying sequence in clutches of tree swallow (Tachycineta bicolor) eggs at a mercury-contaminated site, presumably due to daily replenishment of mercury in females during laying. Sampling just one egg from the nest provided an accurate measure of clutch mercury contamination.