Ionized anilines dissociation

Ionized aniline may exist in a conventional-ion form as well as in isomeric distonic forms, and gas-phase MS experiments performed by Chyall and Kenttamaa134,135 have also been used to form and to study the intrinsic reactivity of these high-energy isomers. Via collision-induced dissociation (CID) of protonated 2-, 3- and 4-iodoanilines in a dual-cell Fourier transform ion cyclotron resonance spectrometer, the 2-, 3- and 4-dehydroanilinium ions were formed as the result of loss of an iodine atom (Scheme 41). Ion/molecule reactions and energy-resolved CID experiments demonstrated that these three ions as well as ionized aniline behave distinctively. The reactivity of three distonic ions... 

In acetic acid it is possible to measure separately the equilibrium constant of proton transfer to form an ion pair and the constant for dissociation of ion pairs to form free ions. [I. M. Kolthoff and S. Bruckenstein, J. Amer. Chem. Soc., 78, I (1956) S. Bruckenstein and I. M. Kolthoff, J. Amer. Chem. Soc., 78, 10 (1956)]. G. W. Geska and E. Grunwald, J. Amer. Chem. Soc., 89, 1371, 1377 (1967) applied this technique to a number of substituted anilines and concluded that the equilibrium constant of the ionization step, rather than the overall acid dissociation constant, is the quantity that should be considered in discussions of effects of structural changes on acidity. 

Two-colour photoionization spectroscopy of aniline cooled in a supersonic jet. Strong propensity for vertical (An = 0) ionization allows vibrational frequencies of CgHgNH2 ( B,) to be determined Two-colour photoacoustic and MPI spectra of aniline, determined as a function of time delay between the two laser pulses. Observed both ionization and dissociation t MPI/TOF mass spectrometric study of phenol. Mechanism of ionization and ion fragmentation t MPI/TOF mass spectrometric study of fragmentation patterns in benzaldehyde. Strong wavelength dependence observed at 266 and 355 nm. Results show operation of two different mechanisms at these excitation wavelengths... 

Ligand Replacement Multidentate by Unidentate.— The cyanide-ion-induced dissociations of [Fe(LL)a] + and [FeCterpy) " ions [LL = phen, bipy, or iV-(2-pyridylmethylene)aniline] were described in Section 4.21. 216 Cyanide ion has a marked stabilizing effect upon the rate of dissociation of [Ni(gga)X] and [Ni(ggg)] ions (gga = NH2CH2CONCH2CONH, X = CN or HjO ggg = triglycinate ion with one proton ionized from each peptide nitrogen atom). The observed rate law is ... 

A more direct approach is to study ionization in solvents of low dielectric constant, such as acetic acid (e = 6.27 at 25°). Then, if the product of ionization is an ion pair, dissociation into free ions is stoichiometrically insignificant. Equilibrium constants for, and proton exchange resulting from ionization have been measured for a series of substituted anilines in acetic acid [50-53]. The results are listed in Table 5. Because the anilines are fairly weak bases, the actual reactant in the kinetic studies is introduced as a p-toluenesulphonate salt, which is in dynamic equilibrium with the acetate salt. 

M ions are observed only for M having not too high IE. Aniline is the typical example. Molecular surface ionization (MSI) is easier not only in the case of a lower IE, but also in the case where a dissociative surface reaction takes place very slowly since the ionization process competes with a pyrolytic surface reaction. The M intensity varies significandy with the work function of the emitter surface. According to this behavior, MSI is a process conveniently described by the Saha-Langmuir equation, no matter whether the MSI process occurs in an equilibrium or in a nonequilibrium. 

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