Timing scheme of the field-cycling experiment. The cycle consists of a relaxation period at field B R during the time τ R (stage 1); switching to evolution field B int during time τ 1 (stage 2), a variable delay time τ at this field (stage 3), switching to detection field B 0 during time τ 2 (stage 4), and detection by applying an RF-pulse and recording the FID (stage 5).
1H NMR spectrum and structure of 5-bromo-2,4-difluoroaniline (BDFA) in acidic D2O. Greek letters indicate spin sub-ensembles of the two fluorine atoms.
NMRD of BDFA protons. Experimental data: open circles—H3 proton, filled circles—H6 protons; color relates to the spin state of the 19F atoms: black—ββ sub-ensemble (a), red—αα sub-ensemble (b), blue—βα, αβ sub-ensembles (c); simulations are shown by solid lines in the respective color.
Energies of the spin levels of two coupled protons characterized by I z = 0 when the hetero-nuclei are in states |ββ⟩ (black) and |αα⟩ (red) (subplot a); and when they are characterized by F z = 0 (blue and green) (subplots b and c). Parameters of calculation were taken from Table I; for convenience we subtracted the large fluorine energy, E F , from the total energy. Solid and dashed lines show the energies of the protons spin states, which correspond to the high-field αH3βH6 and βH3αH6 states, respectively. Blue and green curves correspond to the energies of fluorine spin states, which go to the high-field βF2αF4 and αF2βF4 states, respectively.
Splitting, ΔE, between pairs of coupled spin levels shown in Figure 4 when the hetero-nuclei are in states |ββ⟩ (black) and |αα⟩ (red); and in states with F z = 0 (blue and green lines). Thin solid line shows the minimal possible splitting between the levels equal to J 12 = 0.37 Hz. Color coding of the 19F spin states is the same as in Fig. 4.
Calculated NMRD curves for BDFA protons in the absence (a) and in the presence (b) of 19F spin relaxation; dashed lines—H3 proton, solid lines—H6 protons; color indicates the spin state of 19F atoms: black—ββ sub-ensemble, blue—βα, αβ sub-ensembles, red—αα sub-ensemble. Parameters of calculation were taken from Table I.
Kinetics of polarization transfer of BDFA protons at 0.1 mT (a) and 85 mT (b) after a selective inversion of H3 proton magnetization at B R = 7 T. Polarization is normalized to the largest value. Open circles —H3 proton, filled circles—H6 proton; color indicates spin state of the fluorine atoms in the same way as in Figure 3: |ββ⟩ (black), |αα⟩ (red), and |αβ⟩ or |βα⟩ (blue). Simulations are shown as solid lines with corresponding color.
NMR parameters of 5-bromo-2,4-difluoroaniline.
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