Restricted Rotation Involving the Tetrahedral Carbon. LVI. NMR and Molecular Mechanics Studies on the Stereodynamics of 8,13-Dichloro-9-methoxy-1,4-dimethyltriptycene

Article abstract of DOI:10.1246/bcsj.58.1690

The 400 MHz 1H NMR spectrum of the title compound at -100 deg C in dichloromethane revealed the presence of two isomers in a ratio of 88:12, which results from restricted rotation about the triptycyl-oxygen single bond.The major isomer was assigned to the ap rotamer on the basis of the low temperature 13C NMR spectrum.Dynamic NMR studies gave the activation parameters for the ap<*>+/-sc conversion: ΔH^<*> = 11.9+/-0.5 kcal/mol (1 cal_th = 4.184 J), ΔS^<*> = 2.6+/-2.5 eu, ΔG_200K^<*> = 11.4 kcal/mol.Results of molecular mechanics calculations on the compound are discussed.