Y-ray induced reactions

Also, the y-ray-induced reactions in alcohols, which sometimes lead to the same product, support the attack of ot-hydroxyalkyl radicals on the unexcited heteroaromatic compound. Yields are particularly interesting in the imidazole series, e.g., with caffeine (16). ... 

The photochemical and y-ray-induced reactions of purines and purine nucleosides with 2-propanol lead to substitution of C(CH3).20H... 

Leonov D, Elad D (1974a) Ultraviolet-and y-ray-induced reactions of nucleic acid constituents. Reactions of purines with ethers and dioxolane. J Org Chem 39 1470-1473 Leonov D, Elad D (1974b) Photochemical and y-ray-induced reactions of nucleic acid constituents. Suppression of the reactivity of pyrimidines in the presence of purines. J Am Chem Soc 96 5635-5637... 

Leonov D, Salomon J, Sasson S, Elad D (1973) Ultraviolet- and y-ray-induced reactions of nucleic acid constituents with alcohols. On the selectivity of these reactions for purines. Photochem Photobiol 17 465-468... 

Steenken S, Jovanovic SV, Candeias LP, Reynisson J (2001) Is frank" DNA-stand breakage via the guanine radical thermodynamically and sterically possible Chem Eur J 7 2829-2833 Steinmaus H, Rosenthal I, Elad D (1969) Photochemical and y-ray-induced reactions of purines and purine nucleosides with 2-propanol. J Am Chem Soc 91 4921-4923 Steinmaus H, Rosenthal I, Elad D (1971) Light- and y-ray-induced reactions of purines and purine nucleosides with alcohols. J Org Chem 36 3594-3598 Stelter L, von Sonntag C, Schulte-Frohlinde D (1974) Radiation chemistry of DNA-model compounds, V. Phosphate elimination from ribose-5-phosphate after OH radical attack at C-4. Int J Radiat Biol 25 515-519... 

UV- and y-ray-induced reactions of purines with ethers such as tetrahydrofuran or diox-olancs yield the corresponding 8-substituted purine derivatives. A typical example is given by the formation of 9. ... 

In the -y-ray induced reaction of COCl with ethene, the following products were... 

The preference for the formation of diphosphonates in reactions between trialkyl phosphites and periluoro-(l,2-dichlorocycloalkenes) has been discussed in terms of the ability of a dialkyl phosphonate group to stabilize an adjacent carbanionic site and steric effects have been invoked to account for the fact that a small amount of monophosphonate is present in the product from perfluoro-(l,2-dichloro(grclopentene) and tri-isopropyl phosphite. PoIyfluorocyclobut-1-enyl phosphonates have been obtained as the main products in y-ray-induced reactions between dialkyl phosphites and poly-fluorocyclobutenes. ... 

The mechanism of the photochemical alkylation shows particular characteristics as regards the formation of alkyl radicals, the reaction of these radicals with the heteroaromatic substrates, and the rearomatization of the intermediate products. A variety of alkylating agents (hydrocarbons, alcohols, amines, carboxylic acids, amino acids) have been used for photochemical and y-ray-induced alkylation. " ... 

At 20 °C, for y-ray induced copolymerizations, r, 0.04 for monomer compositions containing 8-39% CO 7). At 120-130 °C, for (C2HsO)2 initiated copolymerizations, tj si 0.15 9). As Eq. (6) indicates, there exists one monomer ratio for which the copolymer composition equals the monomer composition, namely if + [C]/[E]) = 1. Using the above values of r, this azeotropic composition corresponds to 48.5 mol % CO for the y-ray induced copolymerizations at 20 °C (Fig. 1) 7), and si 46 mol % CO for the free radical initiated copolymerizations 9). The value of rj is dependent on the reaction temperature. For example, for the y-ray induced copolymerizations, the value of r2 increases from 0.04 at 20 °C to 0.31 at 157 °C 7). As expected, the value of rt at 135 °C was close to that observed for the free-radical initiated polymerization at that temperature. These results indicate that the copolymerization should be carried out at low temperatures in order to get copolymers with high CO contents. The azeotropic composition is also altered by pressure. For example, for (C2HsO)2 initiated copolymerizations the %CO in the azeotropic composition drops from 46% to 36% when the total gas pressure is lowered from 100 to 13.6 MPa (from 1000 to 136 atm) 9). 

Okamoto and co-workers [45] reported y-ray induced addition reaction of carbon tetrachloride (CC14) to the vinyl group of syndiotactic 1,2 BR. They observed that addition... 

Chiral crystals generated from non-chiral molecules have served as reactants for the performance of so-called absolute asymmetric synthesis. The chiral environments of such crystals exert asymmetric induction in photochemical, thermal and heterogeneous reactions [41]. Early reports on successful absolute asymmetric synthesis include the y-ray-induced isotactic polymerization of frans-frans-l,3-pentadiene in an all-frans perhydropheny-lene crystal by Farina et al. [42] and the gas-solid asymmetric bromination ofpjp -chmethyl chalcone, yielding the chiral dibromo compound, by Penzien and Schmidt [43]. These studies were followed by the 2n + 2n photodimerization reactions of non-chiral dienes, resulting in the formation of chiral cyclobutanes [44-48]. In recent years more than a dozen such syntheses have been reported. They include unimolecular di- r-methane rearrangements and the Nourish Type II photoreactions [49] of an achiral oxo- [50] and athio-amide [51] into optically active /Mactams, photo-isomerization of alkyl-cobalt complexes [52], asymmetric synthesis of two-component molecular crystals composed from achiral molecules [53] and, more recently, the conversion of non-chiral aldehydes into homochiral alcohols [54,55]. 

An interesting new way was shown by °Co y-ray induced copolymerisation of hemin in the presence of another polymer (all reactions controlled by UVAn[S-spectra) . ... 

The apparent activation energy for the y-ray induced formation of carbonyl difluoride is calculated to be 18.0 kj moP . The kinetics results indicate a chain mechanism in which primary radicals formed from the irradiation of CjF, induce its copolymerization with Oj-The resulting long-chain peroxide radicals decompose by splitting off COFj or CjF O, depending upon whether a carbon-carbon, or oxygen-oxygen bond is broken. The perfluorinated cyclopropane is considered to be formed independently, in a minor side-reaction [420]. 

At high conversion, the growth of viscosity hinders the termination by radical-radical reactions, but it has less effect on the propagation reaction, because diffusion of small monomer molecules is not so much affected by viscosity. Hence, both the rate of polymerization and the molecular weight of the polymer show an increase, there is auto acceleration at high conversion. This effect is known as gel-effect or Tommsdorf-effect, which is usually accompanied by a sudden rise of temperature (Swallow 1973). Such effect was observed in many systems, for instance in the y-ray induced steady-state bulk polymerization of methyl methacrylate (Luthjens et al. 2001). 

Mercaptans add across olefinic double bonds in a radical chain reaction. This is a well-known process for modifying unsaturated polymers. A recent report describes the y-ray-induced addition of ethyl mercaptan to the vinyl groups of polybuta-1,2-diene to produce the modified unit (6). Carbon tetrachloride will also add under the same conditions but the reaction is complex, and involves cyclization and cross-linking. 

He) were able to show that some iron meteorites and lunar rocks also have cosmogenic W isotope anomalies that are superimposed on the radiogenic isotope effects. For the lunar rocks, these anomalies were shown to be due to the Ta(n,Y) a reaction, induced by cosmic radiation, whereby the short-lived isotope a (T = 114 days) subsequently decays to [141]. For the iron meteorites, cosmic ray-induced reactions lead to both the production and consumption of various W isotopes. As a result of these reactions, many samples of both magmatic and non-magmatic irons appear to have ratios that are... 

Thiols add to double bonds through a radical chain reaction recent reports " describe the y-ray-induced addition of mercaptoethane to 1,2-polybutadiene to form (3). 

Bulk Polymerization. The spontaneous polymerisation of VDC, so often observed when the monomer is stored at room temperature, is caused by peroxides formed from the reaction of VDC with oxygen. Very pure monomer does not polymerize under these conditions. Irradiation by either uv or y-rays (26,28) also induces polymerization of VDC. 

A beam of charged particles (an ion beam) with an energy from a few hundred keV to several MeV is produced in an accelerator and bombards a sample. Nuclear reactions with low-Z nuclei in the sample are induced by this ion beam. Products of these reactions (typically p, d, t, He, a particles, and y rays) are detected, producing a spectrum of particle yield versus energy. Many (p, a) reactions have energies that are too low for efficient detection. In these cases, the associated y rays are detected instead. Important examples are ... 

In terms of atomic spectrometry, NAA is a method combining excitation by nuclear reaction with delayed de-excitation of the radioactive atoms produced by emission of ionising radiation (fi, y, X-ray). Measurement of delayed particles or radiations from the decay of a radioactive product of a neutron-induced nuclear reaction is known as simple or delayed-gamma NAA, and may be purely instrumental (INAA). The y-ray energies are characteristic of specific indicator radionuclides, and their intensities are proportional to the amounts of the various target nuclides in the sample. NAA can thus... 

In some cases it is possible to differentiate between the various alkyl substituents. Primary, secondary and tertiary nitrates and nitrites all show clearly different infrared absorptions. The spectra of acid fluorides can be used to differentiate chain-end groups from pendant acid groups. Furthermore, the loss of all -OH species upon sulfur tetrafluoride exposure allows the reliable estimation of ketones, esters and lactones without the complication of hydrogen-bonding induced shifts in the spectra. Preliminary results from the use of these reactions to characterize y-ray oxidized polyethylene and polypropylene are used to illustrate the scope of the methods. 

In contrast to PIXE and RBS, where forces are respectively electromagnetic and electrostatic, this kind of microanalysis uses low range nuclear forces. The analysis is based on the detection of the y-rays emitted from nuclei that are in an excited state following a charged particle induced nuclear reaction. 

Matsue et al. [43] attempted to study the molecular rocket reaction in a ruthenocene-/ -cyclodextrin inclusion compound using the I00Ru y, p) "raTc reaction. They noticed a parallel relationship between chemical processes and nuclear-recoil-induced processes in the non-included ruthenocene compound, as shown in Fig. 9. In the nuclear-recoil-induced processes no dimerization can be observed because of the extremely low concentration of the product, whereas in the chemical processes dimerization is possible, as demonstrated by Apostolidis et al. [48]. When ruthenocene included in /J-cyclodextrin is irradiated with y-rays, a part of the ruthenocene molecule is converted to [TcCp2-] which escapes from the jS-cyclodextrin cavity. The [TcCp2] rocket thus produced can attack neighboring inclusion compounds so as to extract the enclosed ruthenocene molecules and abstract H or Cp (Cp cyclopentadienyl radical). This process is shown schematically in Fig. 10. 

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