Singlet oxygen Subject

Recently the solvent effect on the [4+2] cycloaddition of singlet oxygen to cyclic dienes has been subjected to a multiparameter analysis. A pre-equilibrium with charge-transfer character is involved, which is affected by the solvent through dipolarity-polarisability (n ) and solvophobic interactions ( Sjf and Another multiparameter analysis has been published by Gajewski, demonstrating the... 

The phenomenon of fluorescence has been synonymous with ultraviolet (UV) and visible spectroscopy rather than near-infrared (near-IR) spectroscopy from the beginning of the subject. This fact is evidenced in definitive texts which also provide useful background information for this volume (see, e.g., Refs. 1-6). Consequently, our understanding of the many molecular phenomena which can be studied with fluorescence techniques, e.g., excimer formation, energy transfer, diffusion, and rotation, is based on measurements made in the UV/visible. Historically, this emphasis was undoubtedly due to the spectral response of the eye and the availability of suitable sources and detectors for the UV/visible in contrast to the lack of equivalent instrumentation for the IR. Nevertheless, there are a few notable exceptions to the prevalence of UV/visible techniques in fluorescence such as the near-IR study of chlorophyll(7) and singlet oxygen,<8) which have been ongoing for some years. 

Dioxygen could overcome the kinetic barrier of its unpaired electrons and triplet ground state by excitation to its first excited state (xAg), in which all electrons are paired. Unfortunately, this species, referred to as singlet oxygen, is generally too reactive and too short-lived for most situations (lb, lc). However, dioxygen complexation to a transition metal can also result in activation and create stable complexes that can be studied, modified, and used in further reactions in a controlled manner (2). This latter type of activation is the subject of this chapter. 

A. A. Frimer. Chemical Reviews, volume 79, American Chemical Society (1979), p. 3S9. The reactions and their mechanisms of alkenes with singlet oxygen are the subjects of this review. 

The target of singlet oxygen in vivo has been the subject of a huge number of studies as it has the potential to change chemical reactivity, and hence biological function, at many sites. Unsaturated fatty acids, for example, are excellent targets [316] and peroxidation of cell membranes is probably... 

Pyrone (361) reacted with /wra-benzoquinone when subjected to laser irradiation in an oxygen atmosphere to give a mixture of products which included the trioxane (42) (18%) <88JOC4986>. Reaction of compound (371) with singlet oxygen, followed by treatment of the reaction mixture with trimethylsilyl triflate, gave the trioxane (388) (6%) <90CC726>. 

Oxidation with singlet oxygen is subject to sterk effects but can show poor regioselectivity. For example, (+)-3-carene (52) is oxidized to produce a mixture of all three possible regioisomeric hydroperoxides with oxygenation occurring at the face of the allyl systm 0 qx>site the gem-dimethylcyclo-propane unit in each case (equation 22). - ... 

Baeyer ). When 138 was subjected to these conditions, o-dibenzoylbenzene (140) was found to be the only product. Dufraisse and Ecary isolated a precursor of 140, namely the photooxide 219, , which seems to be formed irreversibly - from singlet oxygen ( Ag) and 138. Compound 219 was described as a crystalline solid which exploded on warming to 18°C... 

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