Carbon-13 spin–lattice relaxation in some polyfluoroaromatic compounds

✍ Scribed by M'Hamed Ali Hamza; Guy Serratrice; Jean-Jacques Delpuech

• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 507 KB
• Volume: 16
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270160207

✦ Synopsis

Abstract

Carbon‐13 chemical shifts, spin‐lattice relaxation times and nuclear Overhauser enhancement factors are reported for five polyfluoroaromatic compounds at 28°C. In all cases the relaxation of the fluorine bearing carbon is predominantly dipolar. Effective correlation times are smaller than those of the analogous benzene derivatives by a factor of 3–4, in qualitative agreement with predictions from the Stokes–Einstein diffusion theory. The T~1~ values for the para‐carbon of monosubstituted fluorobenzenes is clearly shorter than the T~1~ values for the ortho‐ and meta‐carbons. This phenomenon was traced to anisotropic tumbling, and D∥ and D⊥ diffusion coefficients were computed using Woessner's equations for molecules assumed to behave like symmetric rotors about their C~2~ in‐plane principal symmetry axis. Equal tumbling ratios, D∥/D⊥, were found in this way for toluene and perfluorotoluene.