Decompositions of Cyclic Structures

The biological availability of contaminating and naturally occurring organic compounds can be estimated by finding their solubility in water. The more soluble the compound, the more available it is for decomposition. While this is true for most organic compounds, there are some that are soluble but also recalcitrant to decomposition. This is the result of complex, sometimes multi-cyclic, structures that inhibit decomposition, such as those of polysaccharides and lignins [2],... 

A homoleptic thioether complex can be prepared by the reaction of perrhenate with 9S3 (15b) in glacial add in the presence of SnCl2. Red-brown crystals of [Re(9S3)2][PF6]2 have been isolated and studied structurally showing a mean Re—S distance of 2.37 A. Treatment of [Re(9S3)2] PF6]2 (268) with ascorbic acid does not result in reduction of the rhenium atom but in its oxidation and the release of ethene by decomposition of the cyclic thioether. The resulting rhenium(III) complex [Re(9S3)(SCH2CH2SCH2CH2S)][PF6] has been isolated and studied by X-ray crystallography. ... 

The present volume comprises 17 chapters, written by 27 authors from 11 countries, and deals with theoretical aspects and structural chemistry of peroxy compounds, with their thermochemistry, O NMR spectra and analysis, extensively with synthesis of cyclic peroxides and with the uses of peroxides in synthesis, and with peroxides in biological systems. Heterocyclic peroxides, containing silicon, germanium, sulfur and phosphorus, as well as transition metal peroxides are treated in several chapters. Special chapters deal with allylic peroxides, advances in the chemistry of dioxiranes and dioxetanes, and chemiluminescence of peroxide and with polar effects of their decomposition. A chapter on anti-malarial and anti-tumor peroxides, a hot topic in recent research of peroxides, closes the book. 

Vitexilactone, obtained from Vi tex cannabifolia (Verbenaceae), has been shown to have the structure (16). It has been correlated with rotundifuran. An interesting iron(ii)-catalysed decomposition of unsaturated cyclic peroxides derived from butadienes leads to 3-alkylfurans. This procedure has been used to convert the peroxide (17) from ds-biformene into the furan (18). Some diterpenoid furans are amongst the constituents of Austroeupatorium inulaefolium (Compositae). These include the diketone austrofolin (19), the corresponding 12-alcohol, and the 15-alcohol (20). A triol, austroinulin (21), was also identified. 

From this compound as well as from other alkylcyclohexanes the yield of ring-opening products is relatively small, about = 0.1-0.4, and G = 0.3-1.6 [108,110] (Table 6), while usually the main decomposition process is the hydrogen formation, which leaves the cyclic structure intact. Here, and with the other alkylcyclohexanes and alkylcyclopentanes, the scission of the ring to smaller molecular mass alkenes and cyclopropane derivates was detected with very low yield. 

Coming to the comparison of the and 0-2 series, the possibilities of isomerization and/or decomposition of the precursor lacunary complexes and, presumably, of their metal ion-substituted derivatives, make it necessary to insure first that no fast conversion occurs, in particular from the a structure to the 2 one. Figure 13(a) compares the cyclic voltammograms of the two lacunary complexes in the pH 3 medium. The main difference appears on the third redox system a single two-electron, reversible wave is obtained for the complex in contrast, the corresponding system for the U2 isomer is clearly constituted by two. 

Finally, Fig. 17 shows the geometry of the cyclic adduct formed by azide with NP, together with the calculated decomposition paths, with different possible intermediates (see Eq. (22)). Although the cyclic structure has been predicted for related metallonitrosyl adducts (82), this was not the case for the reaction with NP, where a... 

From the analyses of NMR and electron-spray ionization mass (ESI-MS) spectroscopy, the polymers obtained from the polymerization of cyclic disulfides were found to be a cyclic structure [202], The cyclic structure consisting of poly(DT) is assumed to be formed by a backbiting reaction of propagating species [203]. Thermal and mechanical properties of the polymers, and decomposition behaviors of the polymers demonstrate that the polymers obtained from thermal polymerization of cyclic disulfides include a polycatenane structure. From polymerization of cyclic disulfides in the presence of cyclic polyethylene oxide), a polycatenane consisting of two different cyclic polymers was obtained [199]. Thus, poly(DT) contains spatial entanglements of cyclic polymers with each other (a polycatenane structure was presumed) (Fig. 61). 

High-temperature heating of the hydrated silicon samples is accompanied by the decomposition of hydroxyl groups and formation of the reactive cyclic structures (=Si-0-)2Si < 02> Si(-0-Si=)2. Their concentration is equal to 10l3cm-2 [4,72]. These groups can also form through the combination (condensation) of two silanone groups ... 

Even though theoretical studies have identified a number of potentially metastable structures [1, 2], the experimentally observed nitrogen compounds are still few. The azide anion, N3, wai. first synthesized in 1890 by Curtius [3]. Christie and coworkers have since 1999 reported the preparation and isolation of Ns"1" together with several different counter ions [4, 5]. A few other species, such as N3, Ns+, N4+, and N6, have been observed only as gaseous or matrix-isolated ions or radicals [6-12], We recently reported the detection of cyclic N5 in a mass spectrometry experiment [13], This observation has later been verified by Christie et. al. in a more elaborate study [14], The experimental preparation and detection of an open-chain N4 molecule was reported in 2002 by Cacace et al [15]. This species is expected to be unstable towards bimolecular decomposition and also too low in energy to be of any greater interest as a HEDM. 

---