Methyl from photolysis

We note, however, that even if methane comes from the photolysis of the methyl ester, this does not necessarily mean that all of it arises as a result of first breaking down the PET itself by photolysis. Both the PET of early reports and also the PECT were undoubtedly produced using dimethyl terephthalate (DMT) instead of terephthalic acid and so have methyl ester end groups owing to the well-known incomplete reaction of the DMT. There may be only a small level of these ester groups, but the amount of methane produced was small as well. This, at the very least, causes some potential confusion about the source of all the methane should some of it come from methyl ester photolysis. No such confusion would exist for the ethane should that be coming from photolysis of an ethyl ester. 

The dimer has been shown by Blackburn and Davies40 to have a geometrical structure similar to that of thymine dimer (10). The proof consisted in observation of the 13C—H satellite NMR spectrum of 5,5 -dideutero-,3,3 -dimethyl uracil dimer (prepared by methylation of the dimer from photolysis of uracil-5-rf). The magnitude of the H6H6 coupling constant showed that these hydrogens were vicinal, and was... 

The homologous azirine (143) with a one-atom bridge gave quite different results.70 Photolysis led to the 3,5-fused bicyclic dihydropyrrole (144). The isomeric azirine (145) also led to (144), although the initial products included dihydropyrrole (146) which apparently converted to (144) as photolysis continued. Azirines (143) and (145) were shown to not interconvert and die postulated two discrete azomethine ylides were trapped with methyl trifluoroacetate. Formation of dihydropyrrole (144) was explained based on a two-step cycloaddition process involving a common diradical intermediate. The observation of (146) from photolysis of (145) but not (143) can be explained based on extinction coefficient differences. Azirine (145) has a high extinction coefficient as does (146). The initial product (146) can then be optically pumped to (144) with a low extinction coefficient. Azirine (143) also has a low extinction coefficient and any (146) that formed from it would be optically pumped to (144) before observa-... 

Formation of Five-Membered Rings via [3 + 2]-Cyc oadditions 255 Table 8.4 Cycloadduct yields from photolysis of stilbene oxides in the presence of methyl acrylate. 

Bell and co-workers 24, 25) have investigated the generation of tri-fluoromethyl radicals from photolysis of HFA in the presence of silanes. Abstraction of the proton is observed in the case of trichlorosilane (24), while methyl(fluoro)silanes lead to the formation of CFjH, CjF, and CF CH 2(25). 

Evidence of primary S-S cleavage is further substantiated in the case of unsym-metrical disulfides obtained from photolysis of mixtures of disulfides In the case of methyl and ethyl disulfides, (methyl ethyl disulfide) = 494, indicating a chain mechanism is operative . 

Methyl-1-phenylcyclopropane (1) was obtained in 33% yield when phenylcyclopropane in tetrahydrofuran was reacted with trimethylsilylmethylpotassium and then with iodo-methane. Photon-induced hydrogen abstraction promoted formation of 7b-phenyl-la,7b-di-hydro-l/f-cyclopropa[a]naphthalen-3(2/f)-one (2) from photolysis of /ra v-l-phenyl-2-(2-oxo-... 

The loss processes (wall deposition and photolysis) make a large contribution of around 50-55% to the measured total loss of most of the compounds investigated. In die case of 5-methyl-2-nitrophenol the contribution was between 29 - 33%. This lower contribution from photolysis and wall loss to the overall loss for this compound can be explained by the higher reactivity of 5-methyl-2-nitrophenol towards OH radical compared to die other nitrocresols. The losses due solely to photolysis were approximately 23-27% in all cases. 

A very low chemical yield of orr/zo-(methylthio)-benzaldehyde was obtained from photolysis of ort/to-methylsulfmylbenzyl alcohol [89], but other relevant experimental parameters (e.g., comparative quantum yields) were not reported. The analogous reaction does not occur with ortho-lo y methyl sulfoxide. The reaction of 163 also proceeds under acetone sensitization. 

Systems of the type [CpM(CO)3R] (M=Group VI metal) have attracted a considerable amount of attention studies have been concerned with both their thermal and photochemical reactions. Scheme 19 shows the principal products obtained from photolysis of the species where R represents methyl or benzyl the primary process is evidently CO dissociation. The photochemical reactions of [CpM(CO)sMe] with ethylene (M = W), acetylene (M = Mo or W), and trimethylphosphine (M = Cr, Mo, or W) have been investigated the results are summarized in Scheme 20. The unusual structure (12), is proposed for the... 

The 3-methyl-2-butene-1-thiol is formed by recombination of a 3-methyl-2-butenyl radical and a thiol radical, possibly derived from sulfur-containing proteins present in beer. The alkenyl radical originates from photolysis of the acyloin group, which is composed of the tertiary alcohol function at C-4 and the carbonyl group of the 4-methyl-3-pentenoyl side chain at C-4 of the iso-alpha acids (Fig. 49). Alternatively,... 

---