Prolonged irradiation

CgHgO, PhCH = CHCOiH. Colourless crystals. Decarboxylales on prolonged heating. Oxidized by nitric acid to benzoic acid. Ordinary cinnamic acid is the trans-isomer, m.p. 135-136 C on irradiation with u.v. light it can be isomerized to the less stable cis-isomer, m.p. 42" C. 

Photoisomerization of perfluoro(4,5-diisopropylpyridazine) is postulated to proceed through Dewar diazabenzenes (25) and (26) to perfluoro(2,5-diisopropylpyrazine) (27), which is in equilibrium with the isomeric perfluoro(2,6-diisopropylpyrazine) (28) after prolonged irradiation in the liquid phase (Scheme 9) (75JCS(P1)1130). Benzo-fused pyridazines do not isomerize readily under photochemical conditions. An exception is perfluorocinnoline which rearranges to perfluoroquinazoline. 

The investigation of the photochemistry of steroidal cross-conjugated dienones was initiated by both Barton and Jeger and was pursued most extensively by the latter group. Despite the frequently complex product patterns which result from prolonged dienone irradiations, some prepara-tively convenient and useful methods for the synthesis of novel systems have been worked out in this field. 

Prolonged irradiation of 1-benzothiepins 3 results in the formation of the secondary photoproducts 4 via a diradical photorearrangement.12,95... 

Curiously, prolonged irradiation of 1,3-dimethyl-5//-pyrazolo[l,2-a]benzotriazolyl-4-ium (108) in benzene in the presence of dipropylamine produces the 2//-azepine 109 rather than the 3H-isomer.192... 

Interestingly, the azepinoazepines 16 and 20 are produced by irradiation of the azidobenz-azcpines 15 and 19 for a short time (5-10 min), whereas prolonged irradiation of the diazidcs results in decreased yields of the azepinoazepinc systems. Photolysis of 1.2-diazido- and 2,3-diazidonaphthalene yield only ring-opened or rearranged products. 

Prolonged irradiation (18 h) of chlordiazepoxide yields the 4//-l,3,6-benzoxadiazocine 19, which is also produced when the oxaziridinobenzodiazepine 13 is exposed to ultraviolet light.240... 

The violet color of the anion radical pair is changed to the yellow color of the anion radical. The replacement of the septet of the adduct by an anisotropic spectrum and the change of the color from violet to yellow occurs also on prolonged standing of a freshly irradiated sample of DMSO-d6 at 77 K ( 15 h8,13). 

A major limitation still remained in this methodology cychzation of hydroxyamides substituted a to the hydroxy group could not be achieved except when the substituent was a mere methyl group, as anything bulkier would prevent the tosylation step, hi this case, using microwave irradiation to force the reaction (Scheme 16) did not prove sufficient, and even after prolonged microwave irradiation at 150 °C no trace of the desired material could be observed. 

An interesting modification of the Pictet-Spengler reaction has been described by Besson and co-workers that employed the degradation of DMSO under microwave irradiation [154]. DMSO undergoes decomposition by prolonged microwave heating, generating dimethyl sulfide, dimethyl disulfide. 

What is the nature of the defects seen in the EPR spectra For alkali and alkali earth halogenides it is well known that irradiation with X-ray, neutrons, gamma-radiation, or electrons produce paramagnetic color centers (F-center) [109-111]. If these centers are created in large amounts, they can be stabilized by the formation of metal clusters as observed for MgCl2 films after prolonged electron radiation [106]. From the temperature dependence... 

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