My PhD dissertation - Institut Fresnel

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31 P NMR settings: It is known that the Nuclear Overhauser Effect (NOE) causes change in the
integration intensity during 1 H decoupling. Thus, all spectra were recorded in a 1 H-nondecoupling
mode. Furthermore, pulse delay time must be long enough to allow complete relaxation of the nuclei
and thus quantitative measurements. Hence, a typical experiment based on the progressive saturation
[ , ]
and saturation recovery 233 234 was applied to the phosphonium salts in order to determine the
minimum spin-lattice relaxation time T1(min.). To insure complete relaxation of all nuclei considered,
the experimental relaxation time T1(exp.) was then set to 5T1(min.). The effective NMR settings used
were data points 32K, spectral width 19000 Hz, pulse width 12.0 µsec (pulse angle 90°), pulse delay
time 30 sec, and number of FID accumulation 256.
In order to evaluate the standard error on the measurements, a calibration was
performed by recording several spectra, in the conditions described above. Twelve sample
mixtures of di-tert-butylmethylphosphine oxide and dibutylmethylphosphine oxide were
prepared by accurate weighting in ratios ranging from 48.7 : 51.3 to 99.3 : 0.7. The accuracy
of the 31 P-NMR quantification was hence checked for ratios close to 1 : 1 mixture, as well as
extreme 99 : 1 cases, by comparing the theoretical ratios to thoses obtained by NMR
integration of the peaks (see Figure 10 – 14 for typical examples). Each sample of phosphine
oxides mixture was recorded three times and an average integration value was used to obtain a
linear regression with a good correlation factor (r² = 0.99):
Theoretica l ratio = 1.01×
Experimental
ratio - 0.50
Theoretical ratio: (48.7:51.3)
Experimental ratio: (48.0:52.0)
Figure 10. Calibration 31 P-NMR spectrum of a (tert-C4H9)2P(O)CH3 / (C4H9)2P(O)CH3