F High-Resolution Nuclear Magnetic Resonance Study of Structure and Properties of Crystalline sy/w-C6Cl3F3

From the high-resolution L9F NMR spectrum of single crystal S}W-C6C13F3 its chemical shift shielding tensor is determined. The most shielded direction lies perpendicular to the molecular plane and the least shielded one in the molecular plane perpendicular to the C-F bond. The most (CT33) and least (an) shielded components change significantly in going from 5vw-C6H3F3 and JJW-C6C13F3 to C6F6 whereas the component in the C -F bond direction (0-22) changes little. It is concluded that the 7r-electron density distribution varies little but the cr-electron density is changed when other substituents are introduced. At 20 °C the 5VW-C6C13F3 molecule rotates about its figure axis and its motion averages out the shielding tensor components within the molecular plane. The mode of the molecular motion does not change at the phase transition point (296 K) and up to the melting point in the time scale of l F high-resolution spectra.