Oxygen sensitive molecules

This reaction introduces the concept of cooxidation. A substrate that is inert under given conditions can decompose under the same conditions in the presence of an oxygen-sensitive molecule. Pure m-stilbene is inert in the presence of oxygen even at a high temperature, whereas /ra .v-stilbene is oxygen-sensitive under the same conditions. In a mixture of the two stereoisomers, m-stilbene reacts at the same rate as its isomer, because it is sensitized by the autoxidation of /ra .v-stilbene. This is because czs-stilbene is inert toward oxygen, but not toward radicals produced by trans-stilbene autoxidation (18). 

In principle, the analysis of molecules, ions and adsorbed intermediates is possible if they survive the emersion (no potential control) and UH V conditions (elimination of most of the solvent). The use of ex situ methods for the analysis of sub-monolayer quantities of oxygen-sensitive substances requires an extremely inert atmosphere when the electrode is emersed. In order to check whether a given adsorbate survives the experimental conditions, a control experiment must be carried out, as we describe here for adsorbed CO on Pt. 

Reduction of flavin by two electrons yields the 1,5-dihydroflavin (Scheme 3), often called reduced flavin . Since isomeric two-electron reduced flavin structures are known (cf. below), the term reduced flavin should be avoided unless defined to prevent misunderstanding. From all flavin species possible in a redox reaction the solution of 1,5-dihydroflavin is, in contrast to that of some isomeric compounds, devoid of a stront colour but not colourless as indicated by the term leucoflavin , which is still used (Table 4). The only true colourless species is (77). Because of the very high oxygen-sensitivity of 1,5-dihydroflavin its chemical and physical properties were investigated only recently Long before crystallographic data on flavins were available, conclusions were drawn from the molar extinction coefficient at 450 nm of 1,5-dihydroflavins with respect to the planarity of the molecules. From the data presented in Table 5 it was proposed that anionic... 

While there are few examples of conjugate additions of either a-oxygen- or a-silyl-stabilized carbanions, Tamao and Posner have reported two hydroxymethyl synthons ["ClfcOH] (246 and 247) which show synthetic promise. Additions with the silicon-based synthon (246) is restricted to 2-cyclohexen-l-ones and work-up requires a successive acid and base procedure that is incompatible with sensitive molecules,188a-b while the tin-based synthon (247) is more versatile and the hydroxyl group is obtained under neutral conditions (Scheme 83).,88c... 

Oxygen is a very effective catalyst for the decomposition " even trace amounts (approximately 10 %) nearly double the rate at 477 °C Oxygen below 10 % has no appreciable influence on the rate . Niclause and Letort studied the oxygen-sensitized decomposition at temperatures (150-400 C) where the acetaldehyde is thermally stable. They pointed out that, even at temperatures as low as 150 °C, the chain length is still appreciable. The number of molecules decomposed per oxygen molecule added changes with the temperature in a characteristic way the approximate values are 140, 210, 65 and 340 at temperatures of 150, 200, 315 and 400 °C, respectively. 

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