Collect. Czech. Chem. Commun. 1999, 64, 44-60

Determination of the Accurate Values of the Rate Constant and Thermodynamic Parameters for the Rotation About the C(sp2)-C(aryl) Bond. 3-Substituted N,N,2,4,6-Pentamethylbenzamides

Eva Přibylová and Miroslav Holík*

Department of Theoretical and Physical Chemistry, Faculty of Science, Masaryk University, 611 37 Brno, Czech Republic


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-dimethylpropanoyl)-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 Ea, ∆H and ∆S lie in relatively narrow confidence intervals.

Keywords: Rate constants; Thermodynamic parameters; NMR line shape analysis; Dynamic NMR spectroscopy; Axial chirality; Hindered rotation.