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Part A. Stereochemical consequences of chlorine substitution reactions with enantiomers in the liquid state. Part B. Molecular mechanics calculations for dl, meso 2,3-dichlorobutanes and 2-halopropionyl halides. Part C. Simultaneous determination of selenite and trimethylselenonium ions in urine by anion-exchange chromatography and molecular neutron activation analysis
Abstract
A. Previously reported recoil halogen-for halogen substitution reactions at asymmetric carbon atoms employing substrate molecules containing two chiral centers in gas, liquid, and solid systems occur with predominant retention of configuration. Subsequent studies on gas phase substitution of energetic $\sp{\rm 34m}$Cl on substrate molecules possessing a single chiral center showed significantly higher inversion yields. This study pertains to high energy substitution event of enantiomeric 2-chloropropionyl chloride molecule in the liquid phase. The net inversion percentage for $\sp{38}$Cl-for-Cl substitution event is 55 $\pm$ 3. The absolute percent yields of $\sp{38}$Cl-labeled products by virtue of (n,$\tau$) in neat liquid substrate molecules are achieved. No conformational effect was observed as proposed in literature. Effect of solvents on the substitution event showed a strong solute-solvent interaction. Strong intermolecular interaction favors substitution via inversion of configuration, whereas solvents of low non-associative dielectric constants seem to inhibit racemization and promote the retention of configuration. B. The conformational energies in dl and meso 2,3-dichlorobutanes and 2-halopropionyl halide molecules have been calculated employing molecular-mechanics techniques. Mole-fractions of the rotational isomers are calculated using conformational energies in gas and solution phases. The results are in fair agreement with the experimental data. C. A method has been developed for the determination of trimethylselenonium (TMSe) ion and selenite (SeO$\sb3\sp{2-}$) ion in urine by anion exchange chromatography, selectively eluting TMSe and SeO$\sb3\sp{2-}$. Since the recoveries are quantitative, a method of additive spikes is employed to determine TMSe and SeO$\sb3\sp{2-}$ ion concentrations in urine specimens. The TMSe and SeO$\sb3\sp{2-}$ chromatographic elutions were collected in vials, irradiated with neutrons and radioassayed for 77mSe activity. The limit of detection is 10 ng Se as TMSe or SeO$\sb3\sp{2-}$ per mL of urine. Thirteen urine specimens from normal subjects were analyzed for TMSe, SeO$\sb3\sp{2-}$ and total selenium concentration.
Subject Area
Analytical chemistry
Recommended Citation
Borkar, Nitin Laxmidas, "Part A. Stereochemical consequences of chlorine substitution reactions with enantiomers in the liquid state. Part B. Molecular mechanics calculations for dl, meso 2,3-dichlorobutanes and 2-halopropionyl halides. Part C. Simultaneous determination of selenite and trimethylselenonium ions in urine by anion-exchange chromatography and molecular neutron activation analysis" (1987). ETD collection for University of Nebraska-Lincoln. AAI8806143.
https://digitalcommons.unl.edu/dissertations/AAI8806143