The unimolecular reactions of the radical cation of dimethyl phenylarsane, C6H5As(CH3)2, 1•+, and of the methyl phenylarsenium cation, C6H5As+CH3, 2+, in the gas phase were investigated using deuterium labeling and methods of tandem mass spectrometry. Additionally, the rearrangement and fragmentation processes were analyzed by density functional theory (DFT) calculations at the level UBHLYP/6-311+G(2d,p)//UBHLYP/5-31+G(d). The molecular ion 1•+ decomposes by loss of a •CH3 radical from the As atom without any rearrangement, in contrast to the behavior of the phenylarsane radical cation. In particular, no positional exchange of the H atoms of theCH3 group and at the phenyl ring is observed. The results of DFT calculations show that a rearrangement of 1•+ by reductive elimination of As and shift of the CH3 group is indeed obstructed by a large activation barrier. The mass-analyzed kinetic energy spectrum of 2+ shows that this arsenium cation fragments by losses of H2 and AsH. The fragmentation of the trideuteromethyl derivative 2-d3+ proves that all H atoms of the neutral fragments originate specifically from the methyl ligand. Identical fragmentation behavior is observed for metastable m-tolyl arsenium cation, m-CH3–C6H4As+H, 2tol+. The loss of AsH generates ions C7H7+ which requires rearrangement in 2+ and bond formation between the phenyl and methyl ligands prior to fragmentation. The DFT calculations confirm that the precursor of this fragmentation is the benzyl methylarsenium cation, 2bzl+, and that 2bzl+ is also the precursor ion fo the elimination of H2. The analysis of the pathways for rearrangements of 2+ to the key intermediate, 2bzl+, by DFT calculations show that the preferred route corresponds to a 1,2-H shift of a H atom from the CH3 ­ligand to the As atom and a shift of the phenyl group in the reverse direction. The expected rearrangement by a reductive ­elimination of the As atom, which is observed for the phenylarsenium cation and for halogeno phenyl arsenium cations, requires much more activation enthalpy.

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An near infrared (NIR) spectroscopy acquisition device was developed in this study using an apple as the test sample. With this device, the apple was rolled while collecting the NIR spectra. The feasibility of using efficient selection of wavelength regions in Fourier transform-NIR for a rapid and conclusive determination of the inner qualities of fruit such as soluble solids content (SSC) of apples was investigated. Graphically-oriented local multivariate calibration modelling procedures called genetic algorithm interval partial least-squares (GA-iPLS) were applied to select efficient spectral regions that provide the lowest prediction error, in comparison to the full-spectrum model. The optimal SSC predictions were obtained from a seven-factor model using five intervals among 40 intervals selected by GA-iPLS. In the determination, a root mean square error of prediction of 0.42 °Brix for SSC of apples was obtained. The result demonstrated that the new method is a very useful and effective method for developing high precision PLS models based on optimal wavelength regions.

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Diary. 1992

Editorial Staff

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No Abstract Available

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Diary. 1992, 1993

Editorial Staff

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No Abstract Available

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Diary. 1992, 1993, 1994

Editorial Staff

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No Abstract Available

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Diary. 1993, 1994

Editorial Staff

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No Abstract Available

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News. NIR news staff recognition.

Editorial Staff

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No Abstract Available

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