Determination of the Accurate Values of the Rate Constant and Thermodynamic Parameters for the Rotation About the C(sp~2)-C(aryl) Bond. 3-Substituted N,N,2,4,6-Pentamethylbenzamides

摘要

Three programs for the ~1H NMR line shape analysis of systems with unequally populated sites have been tested in order to get highly accurate rate constants of the hindered rotation about a single bond using four published criteria. The programs differ in the number of optimized parameters. As test compounds, 3-(adamantan-1-carbonyl)-N,N,2,4,6-pentamethylbenzamide (1) and 3-(2-dimethylpropanoly)-N,N,2,4,6-pentamethylbenzamide (2) were prepared. It was found that a supermodified simplex method with only six parameters optimized in one step gives the most accurate values of the rate constants. Consequently, the calculated thermodynamic parameters E_a' #DELTA#H~not= and #DELTA#S~not= lie in relatively narrow confidence intervals.