Kevill, Dennis N.
M.S. (Master of Science)
Department of Chemistry
Chemistry, Physical organic||Nuclear chemistry
Based on a product study at complete reaction of triethyloxonium ion at 0.0° C, the value of log k₁/k₂ was determined for the competition reaction between varying concentrations of added nucleophile (second-order rate coefficient, k₁) and a solvent ethanol (pseudo-first order rate coefficient, k₂). Using the Swain-Scott equation, log k₁/k₂ = ns (with s = 1), a nucleophilicity scale was constructed for the iodide, thiocyanate, bromide, chloride, nitrate, and p-toluenesulfonate anions, as their tetra-n-butylammonium salts. The values correlate reasonably well with previous scales and include a value for the previously unreported p-toluenesulfonate anion. A plot of log k₁/k₂ versus anion concentration illustrates the perturbation caused by electrostatic interaction between reacting positive and negative ions, and values used in the correlations were obtained by extrapolation to infinitely low added anion concentration. Values of log k₁/k₂ were also determined when the nucleophile was either the parent or a ring substituted N,N-dimethylaniline. In addition to exhibiting no perturbation, due to removal of the electrostatic interaction, a Hammett ρσ plot gave a ρ value of -3.09 which is very similar to the ρ value of -2.86 reported by Kevill and Shen for the reaction of ethyl perchlorate with N,N-dimethylanilines in benzene at the slightly higher temperature of 25° C; if one applies approximate adjustments for the temperature difference, the ρ values are essentially identical and of a magnitude suggestive of appreciable bonding to the nitrogen within the transition state. These correlations are a further example of S[sub N]2 reactions for which the ρ values are independent of the nucleofugality and charge type of the leaving group. The nucleophilicity study of the nitrate anion as its tetrabutylammonium salt was extended to include: 1) silver ion as the counter cation with triethyl- oxonium ion maintained as the substrate, and 2) silver ion as the counter cation with ethyl iodide as the substrate. The product profile and electrostatic interaction curve suggest a common mechanism and, therefore, a S[sub N]2Ag mechanism for the reaction with ethyl iodide.
Fujimoto, Edward K., "Nucleophilicity studies using the triethyloxonium ion as substrate" (1984). Graduate Research Theses & Dissertations. 4145.
Northern Illinois University
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