Ring Inversion in 1,4,7-Cyclononatriene (Trishomobenzene). Force-Field Calculation for Abnormally Large Bond Angles

Article abstract of DOI:10.1021/ja00528a003

The barrier to ring inversion in 1,4,7-cyclononatriene has been measured by 1H dynamic NMR spectroscopy in tetrachloroethylene, 1,1,2,2-tetrachloroethane, and toluene-d₈ as solvents.Values of ΔG^<*> near room temperature vary from 14.5 +/- 0.1 to 14.8 +/- 0.1 kcal/mol.Values of ΔS^<*> vary from -2.2 +/- 2 to -4.9 +/- 2 eu and are not strongly negative (-18.2 +/- 0.1 eu in CDCl3), as previously reported.Values of ΔH^<*> vary from 13.1 +/- 0.5 to 14.1 +/- 0.5 kcal/mol.Calculations with the Boyd force field show that the strain energy of the crown conformation is 4.6 kcal/mol lower than that of the saddle conformation.The barrier for ring inversion is not well reproduced by the calculations, and possible reasons for this are discussed.