Fragmentation photo

Cycloadditions.—Continuing interest has been shown in the photo-oxygenation of adamantylideneadamantane and in the reverse, thermally initiated, chemiluminescent fragmentation. Photo-oxygenation of the olefin affords the dioxetan (313) and the epoxide (312). With /ncso-tetraphenylporphin as sensitizer, (313) is the major product in all the solvents studied, whereas photo-oxygenation of the olefin in acetone and using a variety of dye sensitizers led to marked changes in the (312) (313) ratio. ... 

A comparison of the electron impact (El) and chemical ionization (Cl-methane) mass spectra of 1//-azepine-1-carboxylates and l-(arylsulfonyl)-l//-azepines reveals that in the El spectra at low temperature the azepines retain their 8 -electron ring structure prior to fragmentation, whereas the Cl spectra are complicated by high temperature thermal decompositions.90 It has been concluded that Cl mass spectrometry is not an efficient technique for studying azepines, and that there is no apparent correlation between the thermal and photo-induced rearrangements of 1//-azepines and their mass spectral behavior. 

An interesting carbene, 1-oxobutatrienylidene [25], having cumulated double bonds, has been found by IR spectroscopy in the photolysis (A>230nm) products of matrix-isolated l,2,3,4-pentatetraene-l,5-dione [26] (Maier et al., 1988) (in its turn the unstable dione [26] was generated by thermo- or photo-destruction of compound [27]). The second product was carbon monoxide. The linear structure of the carbene [25] has been suggested on the basis of two intense IR bands at 2222 cm and 1923 cm indicating respectively ketene and allene fragments. 

S., Grzesiek, S., litman, B. J., Bax, A. Measurement of dipolar couplings in a transdudn peptide fragment weakly bound to oriented photo-activated rhodopsin. f. Biomol. NMR 2000, 16, 121-125. 

There was no evidence for production of (n C5H5)Co(C0) in Ar matrices, presumably because of very ready recombination with CO in the matrix cage. Whether a matrix isolated carbonyl molecule can eject CO without automatic reconbination probably requires the photochemical path to lead to a ground state fragment in which the empty coordination site is oriented away from the photo-ejected CO - see the Cr(C0)5 photochemical scheme (Figure 3).]... 

Relative to the most intense photo-dissociation peak ionic fragmentation of the parent molecule is not included. 

In the second dual photo/thermal initiation strategy, the approach described above is augmented by the inclusion of a thermal initiator. Upon illumination, active centers produced by fragmentation of the photoinitiator start the polymerization reaction. The heat evolved from the exothermic photopolymerization elevates the temperature of the system and results in the production of additional active sites by the thermal initiator. This dual initiating strategy provides both the cure on demand (temporal control) afforded by photopolymerization, and the completeness of cure provided by the thermal initiator. 

The simplest form of such photo-dissociation is that when one of the fragments is simply an electron ... 

By convention, the groups of atoms formed during photo-dissociation are usually called fragments. 

We next examine the possible fates of the alkoxy radical produced as a result of hydroperoxide fragmentation. It should be noted that the other fragment produced in this process, an hydroxy radical (not shown), would be an extremely reactive species. Since it is not attached to a polymer chain end, it is also capable of more readily diffusing through the polymer matrix than most of the radicals discussed to this point. This also makes the photo-oxidation of the glycol potentially more destructive. 

The first part of the review deals with aspects of photodissociation theory and the second, with reactive scattering theory. Three appendix sections are devoted to important technical details of photodissociation theory, namely, the detailed form of the parity-adapted body-fixed scattering wavefunction needed to analyze the asymptotic wavefunction in photodissociation theory, the definition of the initial wavepacket in photodissociation theory and its relationship to the initial bound-state wavepacket, and finally the theory of differential state-specific photo-fragmentation cross sections. Many of the details developed in these appendix sections are also relevant to the theory of reactive scattering. 

Figure 19.5 Visualization of DNA damage induction in cultured human keratinocytes by photo-activated lomefloxacin using the comet assay. The presence of DNA breaks (induced either by ROS or by excision of DNA lesions) leads to fragmentation and electrophoretic migration to produce the comet tails, whereas bulky genomic DNA remains in the comets heads.

The photolysis of the meso-ionic 1,4-diphenyl-l,2,4-triazol-3-one (200, R = R = Ph, R = H) was stated to yield phenyl isocyanate (13%), 7V,iV -diphenylurea (23%), and the bicyclic compound 215 (49%). These results were interpreted in terms of the fragmentation of the photo-intermediate 213 yielding the iV-phenyldiazirine (214). A later publication by the same group reports different results. Photolysis of meso-ionic 1,4-diphenyl-l,2,4-triazol-3-one (200, R = R = Ph, R = H) was stated to yield phenylisocyanate and the bicyclic compound 215. Later studies have shown that the bicyclic compound... 

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