Pseudorotation in Cyclopentane. An Experimental Determination of the Puckering Amplitude by NMR in Oriented Solvents

Article abstract of DOI:10.1021/ja00384a008

Proton NMR spectra of normal cyclopentane, 1,2,2',5,5'-pentadeuteriocyclopentane, and randomly deuterated cyclopentane in liquid crystalline solvents between -30 and +110 deg C are reported.The spectra yield all possible distinct average dipolar interactions between the protons in the molecule.These results are compared with the predictions of fife different theoretical models for the dynamic puckering deformation of cyclopentane.Although the general trend in these models is consistent with the experimental results, there is no exact agreemnt between the average dipolar interactions calculated from these models and those obtained experimentally.The experimental results are then subjected to a best-fit analysis in terms of Pitzer's pseudorotation model, using the modification of Adams et al., with the puckering amplitude, q, as a single adjustable parameter.A perfect agreement between the experimental dipolar parameters and those calculated from this model is obtained with q = 0.463 Angstroem.