| Summary: | 碩士 === 國立成功大學 === 化學系碩博士班 === 96 === We have previously proposed the entropy view of the butyl group allowing
ample space for the flow of PF6 anion to account for the large values of Hyper Anion
Preference (HAP) observed for the BMIPF6 ionic liquid system. In order to verify
this entropy argument, the butyl group of BMI cation has been replaced by the
hydroxyethyl group (CH2CH2- OH). The NMR diffusion measurements, 1H-NOESY,
1H,19F-HOESY and spin-lattice relaxation experiments have been extended to the
1-(2-hy -droxyethyl)-3-methylimidazolium hexafluorophosphate (HEMIMPF6) ionic
liquid system.
The HAP values were dropped due to the above-state replacement, which
provides the first supporting evidence of the “Entropy Argument”. This is further
supported by the difference of the 1H,19F-HOESY spectra recorded for BMIPF6 and
HEMIMPF6. The occupation of TFE on butyl in the BMIPF6/TFE mixture will
finally repel the connection of PF6 anion and the butyl through space. For the
HEMIMPF6 analogues, the occupation of TFE on hydroxyethyl group, however,
disappear through analysis of the HOESY spectra. These results are consistent with
the more localized (or less mobile) PF6 anion motion in the HEMIMPF6 ionic liquid
system. In other words, the entropy of PF6 anion decreases as the butyl group is
substituted by the CH2CH2OH.
The localization of PF6 anion has been further verified by the shorter T1 found
for PF6 anion in HEMIMPF6 ionic liquid system compared in the BMIPF6 system
since a more hindered reorientation. The magn- itudes of translation diffusion
measured by PGSE-NMR experiments, again, reveal that PF6 anion is more hindered
in HEMIMPF6 ionic liquid system. Furthermore the changes of chemical shift data
are understood based on the hindered dynamic behaviors of PF6 anion.
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