Determination and application of Winstein-Grunwald M and Y values in bridged polycyclic systems

The rates of solvolysis of 3-nortricyclyl p-bromobenzenesulfonate (nortricyclyl brosylate) have been determined (at 25.0) in the solvents acetic acid, methanol, and acetic acid and methanol with various small amounts of added water. First order rate constants were obtained by u.v. absorbance, conductometric and titrimetric techniques. All rate constants obtained, with the exception of the titrimetric data, were fairly reproducible and agreed with the previously reported data (where available). Numerical values of m from the Winstein equation: log k/k = mY were calculated from experimental data for solvolysis reactions of nortricyclyl brosylate in each of the solvent sets. These m values fell in a range of 0.40-0.69. U.V. absorbance and conductometric data were employed in m value calculations. Results of titrimetric method were inconsistent and were disregarded. Calculated values of m were in the expected range for a secondary substrate. A range of m values was observed depending on solvent and analytical technique employed. The range of m values suggested that less attention should be focused on absolute value of m and greater attention should be directed to the linear correlation fit of log k vs. Y plot (used to determine m). Correlation coefficient data are presented which substantiate this conclusion. The rates of solvolyses of exo-(cis) and endo- ( trans )-3-chloroexo- 5-norborn-5-yl-2,4-dinitrobenzene thioether in acetic acid were also studied using conductometric analytical techniques. The experimentally observed rate constant of the endo-(trans) compound was higher than that of the exo- (cis) compound. These rates determined by others in 70% aqueous dioxane show the cis compound to be more reactive than the trans. It is assumed that these latter results are the normal results and that the results In acetic acid indicate that this solvent is a poor one for determination of stereochemical structure. A rationalization for the reactivity ratio reversal in acetic acid is advanced