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Carbon‐13 spin–lattice relaxation in some polyfluoroaromatic compounds
Author(s) -
Hamza M'Hamed Ali,
Serratrice Guy,
Delpuech JeanJacques
Publication year - 1981
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270160207
Subject(s) - dipole , chemistry , relaxation (psychology) , benzene , spin diffusion , anisotropy , fluorine , molecule , toluene , spin–lattice relaxation , lattice (music) , nuclear overhauser effect , thermodynamics , diffusion , nuclear magnetic resonance , condensed matter physics , computational chemistry , physics , organic chemistry , nuclear quadrupole resonance , quantum mechanics , psychology , social psychology , acoustics
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.