Organocobalt B12 models: axial ligand effects on the structural and coordination chemistry of cobaloximes

The reactivity-selectivity principle (RSP), once a tenet of organic chemistry, eroded during the 1970s and was more or less abandoned by 1980. Although it has been clear for more than 25 years that a decrease in selectivity with increasing reactivity can only be expected with certainty if diffusion control is approached, the RSP has survived as an intuitively appealing rule. This Minireview shows why selectivity cannot generally decrease with increasing reactivity and highlights the weaknesses of the theoretical foundations of the RSP.

The Reactivity–Selectivity Principle: An Imperishable Myth in Organic Chemistry

Although cadmium has been recognized as a highly toxic heavy metal and poses many detrimental effects on human health, the Cd2+-uptake and nosogenesis mechanisms are still insufficiently understood, mainly because of the lack of facile analytical methods for monitoring changes in the environmental and intracellular Cd2+ concentrations with high spatial and temporal reliability. To this end, we present the design, synthesis, and photophysical properties of a cadmium sensor, DQCd1 based on the fluorophore 4-isobutoxy-6-(dimethylamino)-8-methoxyquinaldine (model compound 1). Preliminary investigations indicate that 1 could be protonated under neutral media and yield a resonance process over the quinoline fluorophore. Upon excitation at 405 nm, 1 shows a strong fluorescence emission at 554 nm with a quantum yield of 0.17. Similarly, DQCd1 bears properties comparable to its precursor. It exhibits fluorescence emission at 558 nm (Φf = 0.15) originating from the monocationic species under physiological condition...

Ratiometric fluorescent sensor based on inhibition of resonance for detection of cadmium in aqueous solution and living cells.

Rate and equilibrium constants for the reactions of pyridines with donor-substituted benzhydrylium ions have been determined spectrophotometrically. The correlation equation log k(20 degrees C)=s(N+E), in which s and N are nucleophile-specific parameters and E is an electrophile-specific parameter, has been used to determine the nucleophilicity parameters of various pyridines in CH(2)Cl(2) and aqueous solution and to compare them with N of other nucleophiles. It is found that the nucleophilic organocatalyst 4-(dimethylamino)pyridine (DMAP) and tertiary phosphanes have comparable nucleophilicities and carbon basicities despite widely differing Bronsted basicities. For that reason, these reactivity parameters are suggested as guidelines for the development of novel organocatalysts. The Marcus equation is employed for the determination of the intrinsic barriers of these reactions.

W. J. Galloway

Papers

695. Structure and reactivity in the pyridine series. Part I. Acid dissociation constants of pyridinium ions

696. Structure and reactivity in the pyridine series. Part II. Menschutkin reaction with ethyl iodide in nitrobenzene