DYNAMICS OF 12-CROWN-4 ETHER IN ITS LINCS COMPLEX AS STUDIED BY SOLID-STATE H-2 NMR

H-2 NMR line shape measurements and simulations were used to study large-amplitude motions of 12-crown-4 ether in its solid LiNCS complex. The overall dynamics of the molecule appear to be a composite of two motions occurring independently at slightly different rates. The first motion involves 2-site up-down flips of CH2 groups. In the second motion the whole molecule rotates within itself such that individual -OCH2CH2- units jump to adjacent sites. Both motions are rapid by 242 K. The first motion demonstrates that the disorder observed in the X-ray diffraction study is dynamic, whereas the second motion is diffraction invisible. There is a strong suggestion that the flip motion is actually a conversion between left- and right-handed chiral forms of the pseudo-C-4 conformation of the 12-crown-4.