Cationization spectral features

The second spectrum (figure 3b) displays the spectral features of DPP+ radical cation and provides evidence of DPP spontaneous ionization DPB + HZSM-5 -> DPB + HZSM-5 " (eq. 2). The third spectrum (fig. 3c) exhibits a broad band at 425 nm and is assigned to electron-hole pair formation DPB + HZSM-5 " - DPB HZSM-5 + (eq. 3). 

Isonicotinic Acid. 4. It is difficult to obtain a spectrum of 4 because the neutral form is not very soluble. At low pH, however, the ring nitrogen is protonated (13) and the cationic isonicotinic acid is sufficiently soluble to obtain SERS spectra. A relatively intense spectrum was obtained at -0.20 V with 0.050 M isonicotinic acid, 0.10 M KC1 and 0.10 M HC1. Many of the spectral features seen with other pyridines are present but the inability to vary solution pH made it impossible to investigate the relative surface populations of protonated and unprotonated forms. 

Fig. 18. 75.4-MHz 13C Bloch decay MAS spectra showing the dynamics of the toluenium ion. The cation was synthesized by reacting bromomethane-13C with benzene-13Q on AlBr3 at 233 K. The spectrum at 213 K shows all the peaks for the toluenium ion at 32 (methyl), 50 (C-4), 178 (C-3), 139 (C-2), and 201 ppm (C-l). The peak at 129 ppm was the unreacted benzene-13C6. At 243 K, the peaks were much sharper, and the 138 and 50 ppm peaks were NMR invisible. At 273 K, the spectrum shows two extra peaks at 128 and 73 ppm. All these spectral features are rationalized by the chemical exchange between the para and ortho isomers.

The ultraviolet spectra of aspartame, obtained under various conditions, are shown in Figure 4. The spectral features up to about 225 nm are attributed to end absorption, primarily from the amide and carboxylate carbonyl groups. The benzenoid group is responsible for absorption in the range of 245 - 270 nm, exhibiting maxima at 252.2,257.6 (e = 752, anion s = 727, zwitterion and cation) and 263.0 nm, as well as shoulders at about 247 and 267 nm. There is minimal dependence of absorption on pH, as would be expected for a primary unconjugated amine, except in the end absorption region below 210 nm. 

In optical spectra of emerald (Neuhaus, 1960 Poole, 1964 Wood and Nassau, 1968 Schmetzer and Bank, 1981), Cr3+ CF bands are located near 16,130 cm-1 and 23,530 cm-1 and are assigned to cations in octahedral sites. Similar bands for octahedral V3+ ions in beryl occur around at 16,000 cm-1 and 23,800 cm-1 (Beckwith and Troup, 1973 Schmetzer, 1982 Ghent and Lucchesi, 1987). Spectral features of pink and red beryls in the region 18,000-20,000 cm-1 (Wood and Nassau, 1968) may originate from crystal field transitions in Mn3+ ions in morganite. 

A recent study of Cgo in pulse radiolysis reported a spectral feature at 650 nm, assigned to the radical cation [82], This study apparently did not use a near-IR sensitive detector, so that the strong 980 nm absorption was not observed, and it is possible that this 650 nm absorption is caused by products of radical addition to Ceo- Reaction of triplet Ceo with strong electron acceptors produces an exciplex and the free C o radical cation in benzonitrile [24]. 

Despite the potential, experimental spectra of ELNES and XANES have not been fully utilized in order to monitor the local structural and chemical environment. One of the major reasons is the presence of core-hole effects which leads to a redistribution of the PDOS features [10]. In other words, the presence of this effect has been considered as a bottleneck for the full interpretation of the experimental spectra. For example, O Brien et al. compared their XANES spectra of MgO, o -Al203 and MgAl204 at cation L2,3-edge with theoretical DOS obtained by band calculations, but their unoccupied DOS did not reproduce the experimental spectra [11]. Thus, the origin of the major spectral features was concluded to be the formation of a core exciton, i. e., a bound state of the excited electron due to the presence of a core hole. 

A hybridization scheme for the cyclopropenyl cation which is consistent with these spectral features is illustrated in Figure 1. 

Because the geometry of 122 is similar to that of 118, similar spectral features can be expected with the exception that the two distonic cationic charges result in a higher atom/charge ratio and, consequently, a lower extent of a delocalization into the strained cyclopropyl moieties. Ionization of 122 was performed under similar conditions" " [Eq. (5.17)]. Indeed, the NMR spectroscopic features (deshielding of the methylenes by 71 ppm compared... 

Ionic interactions in ionomers are reflected in their spectra both directly and indirectly. They indirectly influence the spectral features associated with the polymeric backbone and the pendant sites as well as some of the spectral characteristics of polyatomic cations. Studies of these spectral properties are extensive. Ionic interactions are probed more directly by observing the vibrations of the cations at their anionic sites. Ion-motion vibrational bands, which occur in the far-infrared spectrum, have been studied in PFSA (Nation) (1), PEMA (2-3), PSMA (4-5), and PSSA (6) ionomers with a range of cations, ionic site concentrations, and other conditions. The force field elements that can be derived from them reflect how the interionic forces vary with the nature of the ionomer. 

Two kinds of experimental design are conceivable to gain insight into the problem of this complex surface to examine the effect of (1) deionization and subsequent titration of metal cations to bR and its mutants and (2) partial neutralization of the electric charges of the amino acid residues located at the cytoplasmic side by site-directed mutagenesis. As to the former approach, it was shown that the 13C NMR spectra of [3-13C]Ala-bR recorded in the deionized state (pH 4) and at a lowered pH (pH 1.2) are almost the same.5 This is consistent with the view that the removal of surface bound cations results in a lower surface pH. Furthermore, Yonebayashi et al. showed that the 13C NMR spectra of [3-13C]Ala-labeled bR and A160G are almost identical under the condition of the deionized state, in spite of their distinctly different spectral features at neutral pH.105 This is caused by an accelerated fluctuation of the interhelical loops and... 

There have been very few studies on the borepin ring system and accordingly discussions of its aromatic character have been sparse. Balaban and Simon169 calculated a K value (aromaticity constant) of +28, which is much lower than for tropylium cation (+100). Further evidence of aromaticity has been based very much on qualitative interpretations of spectral features. 

Not only the anions but also the cations show an i(Mi specificity at the air-water interface. Wang et al. could demonstrate that the SFG spectra of the water molecules of aqueous electrolyte solution of NaF and KF exhibit different spectral features and different concentration dependences [26]. These data reveal clear cation effects. 

---