Amines in the Gas Phase

The chemistry of ionized, protonated and cationated amines in the gas phase... 

The precursor model of FAB applies well to ionic analytes and samples that are easily converted to ionic species within the liquid matrix, e.g., by protonation or deprotonation or due to cationization. Those preformed ions would simply have to be desorbed into the gas phase (Fig. 9.6). The promoting effect of decreasing pH (added acid) on [M+H] ion yield of porphyrins and other analytes supports the precursor ion model. [55,56] The relative intensities of [Mh-H] ions in FAB spectra of aliphatic amine mixtures also do not depend on the partial pressure of the amines in the gas phase, but are sensitive on the acidity of the matrix. [57] Furthermore, incomplete desolvation of preformed ions nicely explains the observation of matrix (Ma) adducts such as [M+Ma+H] ions. The precursor model bears some similarities to ion evaporation in field desorption (Chap. 8.5.1). 

FIGURE 1. AGh+ °f protonation for primary amines in the gas phase versus IP J... 

FIGURE 2. AG + of protonation for tertiary amines in the gas phase versus IP"... 

Primary Amines. Early studies on the photolysis of primary amines in the gas phase by Bamford (224) in 1939 were resumed by Taylor and co-workers (47,225), and Michael and Noyes (226) using the wavelength region around 200 nm. Studies at 147 nm were undertaken by Magenhelmer et al. (227), and at X 124 nm... 

TABLE 20. Photolysis (x 224-194 nm) of methyl amine in the gas phase (226) (100 torr, room temperature). Quantum yields are based on the hydrogen bromide actinometer. 

Treatment of silylphosphine (68) with amines in the gas phase gives quantitative yields of silylamines. Pyrolysis of (68) (using deuterium labelling)... 

Photoelectron Spectroscopy.—The spectra of the reactive methylidynephosphines (70 R = Ph, TMS) have been compared with the stable tertiary butyl compound. " The vertical ionization potentials of trimethyl-, methylphenyl-, and triphenyl-phosphines have been measured. The basicity order in the gas phase is the reverse of that in solution and of the basicity order of amines in the gas phase. " ... 

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