Carbon from photolysis

Torrents A, BG Anderson, S Bilboulian, WE Johnson, CJ Hapeman (1997) Atrazine photolysis mechanistic investigations of direct and nitrate-mediated hydroxyl radical processes and the influence of dissolved organic carbon from the Chesapeake Bay. Environ Sci Technol 31 1476-1482. 

Eq. 52). It seems likely that the reaction of arc generated C with 93 actually follows this same pathway with the H2 and some CO resulting from photolysis of formaldehyde in the carbon arc. 

Although we could not isolate and characterize a pure product from photolysis of [RuH2(CO)(PPh3)3] in benzene, we could trap the proposed intermediate by irradiation under carbon monoxide. When irradiation was conducted under CO, the ir and 31P NMR spectral changes showed that [Ru(CO)3(PPh3)2] was produced quantitatively (see Reaction 9) (35). The product could be isolated pure by solvent concentration. 

Schemes 5 and 6 outline the functionalization of a 10/1-Me by a steroidal 6/f-ol [1] and a 2/3-61 nitrite [6], Functionalization of 13/i-Me by a 20a-ol nitrite [7] and functionalization in the terpenoid field [8] are outlined in Schemes 7 and 8. The last example involves a 7-membered cyclic transition state that seldom occurs. Scheme 9 outlines a recent application of the Barton reaction in the synthesis of a biologically active carbacepham [9]. The photolysis of acyclic 5-phenyl-1-pentanol nitrite gives, preferentially, a nitroso dimer arising as a result of the abstraction of a hydrogen attached to the d-carbon, rather than the e-carbon from which the better stabilized benzyl radical can be generated (Scheme 10) [10].

The presence of OH radicals, H202 and 03 must cause mechanisms known from photolysis, photocatalysis or ozonation (Langlais et al. 1991). New ROS such as 03 , 02 , O-, H02, H03, HO4 and others are possible most of them are short lived. Interactions with chloride, carbonate, bicarbonate, sulphate and other ions may form longer lived radicals (Gottschalk et al. 2000 Le Truong et al. 2004). The discussion below makes it clear that there are many indications of OH radicals reacting with other ions. 

Torrents, A. Anderson, B. G. Bilboulian, S. Johnson, W. E. Hapeman, C. J. Atrazine Photolysis Mechanistic Investigations of Direct and Nitrate-Mediated Hydroxy Radical Processes and the Influence of Dissolved Organic Carbon from the Chesapeake Bay, Environ. Sci. Technol. 1997, 31, 1476-1482. 

Cyclobutanediones, once exotic compounds represented by a few perhalo derivatives, have become readily available as a result of new synthetic developments in recent years. These include the modified acyloin condensation 52) in which the intermediate enediolate is trapped as bis-trimethylsilyl ether (28) which can be converted to cyclobutanedione by reaction with bromine or hydrolyzed to acyloin and oxidized in a separate step. In addition to this efficient and general method, bi- or polycyclic unsaturated cyclobutanediones (30) have become available from photolysis of bridged cyclohexenediones (29) to be discussed in the following section. Photocycloaddition of dichlorovinylene carbonate (DCVC) to olefins53) promises to provide a third route if the problems associated with hydrolysis of the photoadducts (31) can be overcome. 

Irradiation of asymmetrically substituted A -benzyl-A -isopropyl-aP-unsatu-rated thioamides (102) in benzene solution induces hydrogen abstraction by the alkenyl carbon from the benzyl and isopropyl groups to give a P-thiolactam (103) and 1,3,5-dithiazinane (104) as products. In the solid state, however, photolysis causes hydrogen abstraction from only the isopropyl group to give the isomeric P-thiolactam (105). 

Ab initio calculations performed by Bigot and Roux have led to an alternative mechanism involving two photochemical steps and the intermediacy of an azirine, as shown in Scheme 40 . Hydrogen atom transfer from the enamine nitrogen to the nitrile carbon of 173 would generate diradical intermediate 177, which would then collapse to the postulated azirine 178. In a second photochemical step, the azirine would then undergo carbon-carbon bond homolysis to 179 followed by reclosure to the imidazole 176. In support of this proposed second photochemical step, structurally similar azirines have been shown to undergo facile carbon-carbon bond photolysis . This mechanism does not, however, explain the initial formation of a thermally unstable intermediate with the observed IR stretch, since azirines of this type are thermally stable at room temperature . ... 

The first example in which a temporarily tethered reagent was directed to attack unactivated C-H bonds remote from the tether point was a study of the products from photolysis of esters of benzophenone-4-carboxylic acid 1 carrying long-chain alkyl groups (Scheme 6-1) [31]. The n-tetradecyl ester was attacked over carbons 8-13, with half the... 

The observed acceleration of the rate was then assumed to arise from the increased concentration of barium nuclei. The evidence presented for the presence of barium was the color change in a decomposed sample on exposure to air. The brown color resulting from photolysis gradually turned white on exposure to air (apparently forming barium carbonate). A proposed reaction scheme includes the photoionization of electrons from the barium nuclei ... 

Unlike water, there is no cold trap for methane or H2 on an earthlike planet. Rather, methane and H2 diffuse to the top of the atmosphere and disassociate from photolysis. The H then escapes to space. The remaining carbon makes it back to the surface where it eventually reacts to form more methane. The hydrogen to do this ultimately comes from water. The net reaction is equivalent to disassociating water and having the hydrogen escape to space. 

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