Stereospecific vinyl substitutions occurring by free radical addition-elimination

The free radical chain reaction between cyclohexyl-HgCl and ($\text{E}$) or ($\text{Z}$) MeO₂CCH=CHSnBu₃, MeO₂CCH=CHI, or ClCH=CHHgCl forms MeO₂CCH=CHC₆H₁₁ or ClCH=CHC₆H₁₁ in a stereospecific manner with retention of stereochemistry.     

Pulsed amperometric detection of sulfur-containing pesticides in reversed-phase liquid chromatography

Pulsed amperometric detection at a gold electrode is demonstrated for the separation of eight sulphur-containing pesticides on a C-18 reversed-phase column with 50% (v/v) acetonitrile in acetate buffer (pH 5.0) as the mobile phase. Detection was based on a two-step potential waveform with adsorption of the analyte during cathodic polarization and subsequent amperometric detection catalyzed by oxide formation following anodic polarization. The mechanism of the anodic detection involves prior adsorption of the sulfur compounds. Hence, the shape of the calibration curve is strongly influenced by the adsorption isotherm of the analyte and, therefore, deviates from linearity at high concentrations. Detection limits below 100 ng ml^?1 in 20-μl samples (e.g., 0.8 ng of dimethoate) were obtained by using preconcentration from a larger sample onto a C-18 fore column prior to injection into the separation column.