Ionized anilines

Rate constants for quenching of triplet erythrosin (an acidic dye of the xanthene series) by a series of anilines were found to correlate with the aniline ionization potential (32). 

Substituent on aniline Ionization energy (eV) (method) Proton affinity (kJ mol 1)... 

We turn now to the ionization process of a series of methyl mono-substituted ring systems pyridines, anilines, phenols, and substituted benzoic acids. Table 2 shows the free energies, A G, the heats, A H, and entropies of ionization, A S, for a number of these compounds. The compounds fall into two classes, according to the different ionic nature of the ionization process. The pyridine and aniline ionizations are of the type... 

Fehrensen B, Hippier M and Quack M 1998 Isotopomer selective overtone spectroscopy by ionization detected IR + UV double resonance jet-cooled aniline Chem. Phys. Lett. 298 320-8... 

Biggs and Robinson give 0.983 and 0.874 based on ionization of anilines and phenols, respectively. 

Jaffe (1953)52 showed that while many rate or equilibrium data conform well to the Hammett equation (as indicated by the correlation coefficient), many such data are outside the scope of the equation in its original form and mode of application. Deviations are commonly shown by para-substituents with considerable + Rot — R effect53. Hammett himself found that p-NOz (+ R) showed deviations in the correlation of reactions of anilines or phenols. The deviations were systematic in that a a value of ca. 1.27 seemed to apply, compared with 0.78 based on the ionization of p-nitrobenzoic acid. Other examples were soon discovered and it became conventional to treat them similarly in terms of a duality of substituent constants . 

The current methodology to determine residues of alachlor, acetochlor, propachlor, and butachlor in crops and animal products was developed over the last two decades by researchers at the Monsanto Company. These herbicides degrade rapidly in plants and animals to numerous metabolites that can be hydrolyzed to common aniline moieties. Little to no parent herbicide is found as intact residue in crops and animal products therefore, the residue methodology focuses on the determination of the common moieties that are derived from the parent herbicides and their metabolites. Initially, gas chromatography (GC) with flame ionization detection, nitrogen-phosphorus... 

TABLE 9. Ionization potentials IP (eV) and orbital energies e (eV) of aniline... 

Similar experiments reveal that ionized N-heterocycles such as pyridines eliminate HCN, rather than HNC148. This distinction offers a potentially useful means of distinguishing between isomeric anilines and pyridines. 

When ionized aminopyridines are considered, it is found that they resemble ionized anilines. Thus, all three isomers of C5NH4NH2"1" eliminate HNC moreover, their distinct CID and CS spectra indicate that these three isomers of CsNRtN "1" do not interconvert before fragmenting151. 

In the ionization of the p-nitroanilinium ion, the free base is stabilized by delocalization of electrons involving the canonical structure 13. An analogous structure is not possible for the p-nitroanilinium ion. In the ionization of p-nitrophenol, analogous delocalization is possible in both phenol and phenate species, but is more marked in the ion. Thus, in both the aniline and the phenol system P-NO2 is effectively more electron-attracting than in the ionization of benzoic acid, where the reaction centre is incapable of a —R effect, and indeed shows a small +R effect (14). 

The mass spectrum of aniline has been known since the early days of mass spectrometry. [122] Initially, the observed [M-27] ion has been interpreted in terms of HCN loss (Fig. 6.56a). The mechanism for loss of the elements of [H, N, C] from aminoarenes is perfectly analogous to CO loss from phenols (Chap. 6.9.1). [231] More recently, it could be demonstrated that loss of hydrogen isocyanide, HNC, occurs rather than losing the more stable neutral species HCN, a behavior typical of ionized pyridine. [222]... 

Figure 3.14 Disposition of benzoic acid and aniline in gastric juice and plasma. Figures represent proportions of ionized and nonionized forms.

Aniline is therefore not absorbed under these conditions (Fig. 3.14). Furthermore, the ionization in the plasma does not facilitate diffusion across the membrane, and with some bases, secretion from the plasma back into the stomach may take place. The situation in the small intestine, where the pH is around 6, is the reverse, as shown in Figure 3.15. 

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