Knowledge Bank

The molecular structures of gaseous cyclopentane and tetrahydrofuran have been studied. Experimental diffraction intensities can be explained by a pseudorotation model similar to that proposed by Pitzer. A modified model maintaining the constancy of the ring bound lengths independent of the pseudorotation phase angle and amplitude of puckering, was adopted. Calculated according to this model, the spectrum of internuclear distances of these molecules is independent of the phase angle of puckering to within the accuracy of the diffraction data. Amplitudes of puckering found for cyclopentane and tetrahydrofuran are, respectively, $q=0.44\backslash AA$ and $q=0.38\backslash AA$, where q is calculated as defined in Pitzer's pseudorotation equation $zi=2/5q\cos 2(2\pi 5j+\varphi )$. The carbon-carbon bond length observed in cyclopentane is significantly longer than that in n-hydrocarbons, whereas the bond lengths in tetrahydrofuran are normal to within experimental error. Possible explanations of the abnormal bond length will be discussed.