Alkane decompositions spectroscopy

One of the potential values of the fast IR studies is to identify trends in alkane coordination. For example, through direct observation of alkane complexes and their decomposition, complexes that most strongly bind alkanes can be identified. The direct observation of a series of heptane complexes with supporting aromatic and carbonyl ligands revealed that CpRe(CO)2(alkane) complexes are relatively stable (Table 11.3).104 This was determined by monitoring the rate of disappearance of metal-alkane complexes, given as k in Table 11.3. These results provided an important lead to the first observation of an alkane complex using NMR spectroscopy (see Section 11.4.2). 

The next section will deal briefly with experimental techniques many of these have been introduced already, but the use of vibrational spectroscopy and of sum-frequency generation call for some further description. Section 4.4.1 describes the principal types of adsorbed hydrocarbon structure that have been found with alkenes and alkynes (aromatic hydrocarbons and cyclic Ce species will be considered in Chapters 10 and 12 respectively) Section 4.4.2 discusses the conditions under which the several chemisorbed forms of alkenes make their appearance. In Section 4.5 we look at detailed structural studies of a few adsorbed molecules, and Section 4.6 deals somewhat briefly with interconversions and decompositions of adsorbed alkenes, and structures of species formed. Finally there are sections on theoretical approaches (4.7), on the chemisorption of alkanes (4.8), and carbonaceous deposits that are the ultimate product of the decomposition process (4.9). 

The ehemieal reaction of zinc dithiophosphate has been studied using in situ ATR FTIR spectroscopy as well as with imaging XPS and ToF-SIMS. In situ ATR FTIR confirms the existence of a decomposition pathway that proceeds through the elimination of alkanes under pure thermal conditions. The reaetion product is zinc polyphosphate. Under conditions of mild mechanical stress at high temperatures, as well... 

Quack, M. andW. Kutzelnigg (1995). Molecular spectroscopy and molecular dynamics— theory and experiment. Ber. Bunsenges. Phys. Chem. Chem. Phys. 99, 231. Rahinovitch, B. S. and D. W. Sester (1964). Unimolecular decomposition and some isotope effects of simple alkanes and alkyl radicals. Adv. Photochem. 3, 1. 

Montmorillonites modified with alkyl pyridinium, imidazolium and phosphonium intercalants were successfully synthesized. Compared to commercial Cloisite 20A, enhancements in thermal stability of +31°C to +70°C were observed in inert atmosphere. The products evolved upon thermal decomposition of the various organoclays were analyzed by mass spectroscopy. Preliminary results indicate that the major part of the volatile by-products is constituted by alkenes and alkanes. Chloromethane was detected between 200°C and 280°C in unpurified Cloisite 20A. CiePy-MMT was found to liberate pyridine above 220°C. Such informations can be of considerable interest regarding the processing conditions of polymer nanocomposites and their subsequent applications. 

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