Photochemical Decomposition of

For O3, two equivalent increased-valence structures 57 and 69 can be For simplicity, both FenO species in VB structure 66 are displayed for 5 = Ms= 1, each of which involves one Slater determinant. According to Eq.(18), S = 1 with Ms =0 and +1. S = 1 with Ms = 0 involves two Slater determinants, to give two (S = 1 S = 0)/2 VB structures . 

Photochemical dissociation of O3 can generate C 2(3Eg ) + 0(3P) as well as 02(1Ag) + 0( D) [50]. A low-energy 5 = 0 excited state has 2 symmetry. In terms of resonance between the increased-valence structures, the wavefunction for this state is F(1i 2) = 57 - 69. which can be expressed according to Eq.(23), 

Increased-valence structure 79 retains the double-bond character for each of the O2 moieties. This structure also involves fractional intermolecular 0=0 bonds - their a and n bond-numbers are both equal to 0.25 [43] - thereby implying that the latter bonds should be substantially longer than normal 0=0 bonds. These bond properties are in accord with calculated estimates of the 0-0 bond-lengths for O4 (1.21 and 3.2-3.5 A [43]). However the results of ST0-6G VB calculations show that the and n y-n y spin-pairings alone are 

By analogy with S2O2 and O4, an S = 0 state for Fen02FeH, with an increased-valence structure of type 65, but with opposed spins for the two 

With S=S replacing 0=0 in VB structure 78, the primary increased-valence structure for C2 symmetry S2O2 is obtained [2,4,51]. 

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Table B2.5.5. The photochemical decomposition of methyl radicals (UV excitation at 216 nm). ris tire wavenumber linewidth of the methyl radical absorption and /ris the effective first-order decay constant [54].

Thermal and photochemical decomposition of peroxides (4) and (5) lacking a-hydrogens (those derived from ketones) produces macrocycHc hydrocarbons andlactones (119,152,153). For example, 7,8,15,16,23,24-hexaoxatrispiro [5.2.5.2.5.2] tetracosane (see Table 5) yields cyclopentadecane and oxacycloheptadecan-2-one. 

Photochemical decomposition of riboflavin in neutral or acid solution gives lumichrome (3), 7,8-dimethyl all oxazine, which was synthesized and characterized by Karrer and his co-workers in 1934 (11). In alkaline solution, the irradiation product is lumiflavin (4), 7,8,10-trimethyhsoalloxazine its uv—vis absorption spectmm resembles that of riboflavin. It was prepared and characterized in 1933 (5). Another photodecomposition product of riboflavin is 7,8-dimethy1-10-foTmylmethy1isoa11oxazine (12). 

There are few reports of the thermal and photochemical decomposition of simple azetidines. 

The thermal or photochemical decomposition of A -haloamines containing a d- (ore-) H-atom represents the earliest example " offunction-... 

Depending on structure, photolysis of films of arenediazonium fluoroborates and hexafluorophosphates at room temperature gives aryl fluorides m 10-75% yield [32] In situ photochemical decomposition of arenediazonium fluoroborates... 

The Hofmann-Loffler-Freytag reaction represents formation of pyrrolidines or piperidines by thermal or photochemical decomposition of protonated A -haloamines in the presence of strong acid such as sulfuric acid or trifluoroacetic acid. " The Hofmann-Loffler-Freytag reaction may also be carried out in milder conditions, for example, PhI(OAc)2,12, hv as shown in section 2.3.4. 

The thermal (or photochemical) decomposition of the azo group gives rise to a radically initiated polymerization. The reactive site F, the transformation site, however, can, depending on its chemical nature, initiate a condensation or addition type reaction. It can also start radical or ionic polymerizations. F may also terminate a polymerization or even enable the azo initiator to act as a monomer in chain polymerizations. 

Electrolysis, and thermochemical and photochemical decomposition of water followed by purification through diffusion methods are expensive processes to produce hydrogen. 

The kinetics and mechanism of the thermal and photochemical decomposition of dialkyldiazenes (15) have been comprehensively reviewed by Engel. The use of these compounds as initiators of radical polymerization has been covered by Moad and Solomon2 and Sheppard.50 The general chemistry of azo-compounds has also been reviewed by Koga et cr/./11 Koenig,3 and Smith.3J... 

Thermal or photochemical decomposition of azonitriles (e.g. AIBN) affords o-cyanoalkyl radicals (Scheme 3.71 ).29... 

The reactions of /-butoxy radicals are amongst the most studied of all radical processes. These radicals are generated by thermal or photochemical decomposition of peroxides or hyponitrites (Scheme 3.75). 

Aroyloxy radicals are formed by thermal or photochemical decomposition of diaroyl peroxides (see 3.3.2.1) and aromatic peroxyesters (3.3.2.3) (Scheme 3.78) alkoxycarbonyloxy radicals are similarly produced from peroxydicarbonates (33.2.2). 

Thiyl radicals are formed by transfer to thiols or by thermal or photochemical decomposition of disulfides (Scheme 3.84). 

Boddington and Iqbal [727] have interpreted kinetic data for the slow thermal and photochemical decompositions of Hg, Ag, Na and T1 fulminates with due regard for the physical data available. The reactions are complex some rate studies were complicated by self-heating and the kinetic behaviour of the Na and T1 salts is not described in detail. It was concluded that electron transfer was involved in the decomposition of the ionic solids (i.e. Na+ and Tl+ salts), whereas the rate-controlling process during breakdown of the more covalent compounds (Hg and Ag salts) was probably bond rupture. 

Branching. Photochemical decomposition of D6-acetone yields CD3, which can then react with acetone or with an added hydrocarbon 43... 

Partial photochemical decomposition of racemic alkyl aryl sulphoxides in the presence of chiral amines as sensitizers gave non-decomposed sulphoxides in optically active form with optical purity of about 3%339. The report340 on the use of cholesteric liquid crystalline reaction media to change the enantiomeric composition of racemic sulphoxides at high temperatures could not be reproduced341. 

The oxygen atoms are produced by the photochemical decomposition of N02, an emission product of automobile engines ... 

Besides thermolysis, the photochemical decomposition of solid trihalo-methylmercury compounds RHgCCli, CF3HgOCOCF3 and Hg(OCOCF3)2 has been studied (Scheme 2). The irradiation of samples placed in an evacuated quartz tube, which was connected to a helium cryostat, was carried out at -50 to +10°C. Thus, a desorption into the gas phase of the primary products of the photolysis occurred, and consequent low-temperature matrix stabilization of them was made. As a result, the formation of only the radicals CCI3 (1 3 898 cm" ) and CF3 (vi 1084, V2 702, P2+ V4 1205, r>3 1249 cm ) or of products of their secondary reactions was observed (Mal tsev et al., 1974, 1975, 1977b). 

Although Ce(IV) oxidation of carboxylic acids is slow and incomplete under similar reaction conditions , the rate is greatly enhanced on addition of perchloric acid. No kinetics were obtained but product analysis of the oxidations of -butyric, isobutyric, pivalic and acetic acids indicates an identical oxidative decarboxylation to take place. Photochemical decomposition of Ce(IV) carbo-xylates is highly efficient unity) and Cu(ll) diverts the course of reaction in the same way as in the thermal oxidation by Co(IIl). Direct spectroscopic evidence for the intermediate formation of alkyl radicals was obtained by Greatorex and Kemp ° who photoirradiated several Ce(IV) carboxylates in a degassed perchloric acid glass at 77 °K in the cavity of an electron spin resonance spectro-... 

There has been considerable interest in the photochemical decomposition of perflnori-nated compounds that have become nbiqnitons. 

Hori H, A Yamamoto, S Kutsuna (2005b) Efficient photochemical decomposition of long-chain perfluorocarboxylic acids by means of an aqueous/liquid COj biphasic system. Environ Sci Technol 39 7692-7697. 

One of the main challenges in the field is the controlled crystalhzation of the nanoparticles into 3D super-lattices, similar to artificial opals but including much smaller individual particles. For this we have used electrically charged stabihzers (ligands and surfactants). For example, the photochemical decomposition of the precursor [Sn(NMe2)2]2 in the presence of HDA... 

Reaction of diazo compounds with a variety of transition metal compounds leads to evolution of nitrogen and formation of products of the same general type as those formed by thermal and photochemical decomposition of diazoalkanes. These transition... 

Carbenes from Sulfonylhydrazones. The second method listed in Scheme 10.8, thermal or photochemical decomposition of salts of arenesulfonylhy-drazones, is actually a variation of the diazoalkane method, since diazo compounds are intermediates. The conditions of the decomposition are usually such that the diazo compound reacts immediately on formation.147 The nature of the solvent plays an important role in the outcome of sulfonylhydrazone decompositions. In protic solvents, the diazoalkane can be diverted to a carbocation by protonation.148 Aprotic solvents favor decomposition via the carbene pathway. 

Alkanes are formed when the radical intermediate abstracts hydrogen from solvent faster than it is oxidized to the carbocation. This reductive step is promoted by good hydrogen donor solvents. It is also more prevalent for primary alkyl radicals because of the higher activation energy associated with formation of primary carbocations. The most favorable conditions for alkane formation involve photochemical decomposition of the carboxylic acid in chloroform, which is a relatively good hydrogen donor. 

The thermal, but not the photochemical, decomposition of ferro-cenylsulphonyl azide (14) in benzene gave some intermolecular aromatic substitution product FCSO2NHC6H5 (6.5%) but no intermolecular cyclization product (17). Contrariwise, photolysis of 14 in benzene gave 17 but no anilide 1 ). 

Emeleus HJ, Taylor HS (1931) The photochemical decomposition of amines and the photochemical interaction of amines and ethylene. J Am Chem Soc 53 3370-3377... 

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