Ortho effects: A mechanistic study

Barkow A, Pilotek S, Grützmacher H-F. Ortho effects: A mechanistic study. EUROPEAN MASS SPECTROMETRY. 1995;1(1):525-537.The fragmentation mechanism of the loss of a water molecule from the radical cations of 2-methylbenzylalcohol 1, 2-methylbenzoic acid 2, and some related compounds 3-9 by an ortho effect is studied. The analysis of the MIKE spectra together with specific deuterium labelling studies and assisted by semi-empirical calculations reveal a continuous spectrum of mechanisms of the ortho effect ranging from a two-step mechanism with a rate determining final loss of the neutral fragment and a rate determining 1,5-hydrogen transfer in the first step entailing a large reverse activation energy to a presumably concerted 1,4-elimination with a more or less asymmetric high energy transition state, These mechanisms cause a different behavior of metastable ions with respect to the kinetic energy release (KER) during the fragmentation by an ortho effect, In the case of a rate determining last step as established for the 1,4-elimination of NH3 from the molecular ions of 2-methylbenzylamine 8 the absence of a reversed activation energy ensures ''normal'' KER behavior and narrow Gaussian shaped peaks in the MIKE spectra, The other mechanisms of the ortho effect exhibit a significant reverse activation energy originating in a barrier of the initial 1,5-hydrogen transfer of the ortho effect, Consequently, large values of the KER are observed for this elimination process in the MIKE spectra of the precursor ions, However, the kinetic energy release distribution (KERD) during the dissociation depends on the stability of the intermediate distonic ion created by the 1,5-hydrogen migration, A well-defined and stable distonic ion as an intermediate leads to flat topped peaks and a large KER which is typically observed for the elimination of H2O in the MIKE spectra of the molecular ions of 2-methylbenzylalcohol 1 and related 2-alkylbenzylalcohols. In the case of a very short life time of the intermediate ion generated by the initial 1,5-hydrogen shift the mechanism can not be discriminated from a concerted 1,4-elimination of H2O with a more or less asymmetric transition state. This situation is typically for the Fragmentation of ionized 2-methylbenzoic acid 2 and related 2-alkylbenzoic acids, and a broad, nearly triangular signal is observed in the MIKE spectrum of these molecular ions

Synthesis and characterization of new cyclopentadienylarsenic compounds

Jutzi P, Pilotek S, Neumann B, Stammler H-G. Synthesis and characterization of new cyclopentadienylarsenic compounds. JOURNAL OF ORGANOMETALLIC CHEMISTRY. 1998;552(1-2):221-228.The new cyclopentadienylarsanes (CpAsR2)-As-x (Cp-x = Me5C5, R = H1, Et2, (i)Pr3, (t)Bu4; Cp-x = Me3H2C5, R = Cl5, Et6, (i)Pr7) were synthesized via metathesis reactions in satisfactory to good yields. 2-7 were characterized by H-1- and C-13-NMR-spectroscopy, mass spectrometry and CH-analysis. The dihydrido compound 1 is stable at room temperature for a short time only, it decomposes already at -70 degrees C under formation of an As-film. The solid-state structure of 4 as well as temperature dependent H-1- and C-13 NMR-spectra indicate steric overcrowding. 4 crystallises in space group P2(1)/c, a = 12.021(2) Angstrom, b = 9.488(2) Angstrom, c = 16.972(2) Angstrom, beta = 110.830(10)degrees, V = 1809.2(5) Angstrom(3), Z = 4, RF = 0.0483. Pyrolysis-studies on the cyclopentadienyl(dialkyl)arsanes 2-4, 6 and 7 show their potential suitability as precursors in the MOCVD-and the MOMBE-process

Hydrorepellent finishing of cotton fabrics by chemically modified TEOS based nanosol

Hydrorepellency was conferred to cotton fabrics by an hybrid organic-inorganic finishing via sol-gel. The nanosol was prepared by co-hydrolysis and condensation of tetraethoxysilane (TEOS) and 1H,1H,2H,2H-fluorooctyltriethoxysilane (FOS), or hexadecyltrimethoxysilane (C16), as precursors in weakly acid medium. The application on cotton was carried out by padding with various impregnation times, followed by drying and thermal treatment, varying the FOS add-on from 5 till 30 % on fabric weight or C16 add-on from 5 to 10 %. Treated samples were tested in terms of contact angles, drop absorption times, washing fastness and characterized by SEM, XPS and FTIR-ATR analyses. In the case of FOS modified nanosol applied with an impregnation time of 24 h or C16 modified nanosol, water contact angles values very close or even higher than 150° were measured, typical of a superhydrophobic surface. The application of the proposed sol-gel process yielded also a satisfactory treatment fastness to domestic washing, in particular for FOS modified nanoso