Solvent molecules, charge trapping

In the previous four sections, several solvent radical ions that cannot be classified as molecular ions ( a charge on a solvent molecule ) were examined. These delocalized, multimer radical ions are intermediate between the molecular ions and cavity electrons, thereby bridging the two extremes of electron (or hole) localization in a molecular liquid. While solvated electrons appear only in negative-EAg liquids, delocalized solvent anions appear both in positive and negative-EAg liquids. Actually, from the structural standpoint, trapped electrons in low-temperature alkane and ether glasses [2] are closer to the multimer anions because their stabilization requires a degree of polarization in the molecules that is incompatible with the premises of one-electron models. 

All the ion and solvation changes discussed so far in this section relate to chemically reversible processes. Anecdotally, it is widely accepted in the redox polymer modified electrode literature that the first redox cycle of a newly deposited film is atypical. Although the reasons and processes are chemically rather different, this is reminiscent of the first cycle effect discussed in Sect. 2.7.3.6 for Prussian Blue films. PVF provides a typical example of this first cycle, or break-in , effect. The initial EQCM response to PVF oxidation in water (after its deposition from an organic solvent, typically dichloromethane) is quite different from that of a previously cycled film [132]. The result is most clearly demonstrated by considering the mass flux - or, better stiU, the difference between the total mass flux and the elec-tron/ion flux-as a function of apphed potential or film charge. Such plots show a once-only pulse of solvent into a new film this solvent (typically ca. five solvent molecules per ferrocene redox site) is retained ( trapped ) within the film thereafter and provides the baseline upon which subsequent redox-driven solvation... 

The relationship of the nitrous acid and nitrosoamide methods of deamination is more tenuous in water since only one example of the i nitrosoamide decomposition in aqueous media has been reported. The decomposition of A -nitroso-A -n-propylbenzamide in dimethyl-formamide-water (60/40 by vol) yielded a propyl benzoate fraction containing 9% of the isopropyl isomer and a propanol fraction con- taining 33% of isopropyl alcohoP . The nitrous acid deamination of n-propylamine under the same conditions yielded an alcohol fraction containing 31% of isopropyl alcohoP. The similarity in the isomer contents of the alcohol portions suggests that common intermediates were involved. The less extensive isomerization of the benzoates may be a reflection of the shorter lifetime of the propyl cations trapped by negatively charged coimter ions compared to those trapped by neutral solvent molecules on the other hand, the role of diazopropane must be determined before definitive conclusions are possible. 

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