-The solid-state photolysis of oxiranes and aziridines produces highly colared ylide intermediates. The stability of these intermediates is dependent an a combination of electronic and steric factors as well as the solid-state constraints of the environment.Flash photolysis studies indicate that two different ylides can be produced in solution at room temperature. These intermediates appear to be identical to those formed consecutively in the solid state or lowtemperature glasses. By the use of certain gas-solid reactions, it is possible to control the lifetime of the intermediate so that it is destroyed immediately or continues to exist almest indefinitely. INTRODUCTIONThe room temperature photolyses of aryloxiranes have been shown by Griffin and co-workers to involve a two-bond cleavage producing aryl carbenes and carbonyl compounds (3,4). On the other hand, the thermal transformations of aryl aziridines were interpreted by Reine (5) and Huisgen (6) as one-bond cleavages producing azomethine ylide intermediates which could be trapped with suitable dipolarophiles.Our previous interest in low temperature and solid-state photochemical techniques (7-9) suggested the possibility of obtaining direct physical evidence for the above intermediates an photoreactions carried out at 77°K. The results of several of these studies already have appeared (10-13) and this report will describe additional recent werk with special emphasis an the relation of the low-temperature studies to the unusual room•temperature solid-state photochemistry which is exhibited by many of the compounds. LOW TEMPERATURE PHOTOCHEMISTRY OF ARYL OXIRANESThe room temperature photochemistry of aryloxiranes has been studied extensively by Griffin and co-workers (3,4). The reactions involve a cycloelimination an photolysis in solution to give aryl carbenes and carbonyl compounds. H /H~ )c=otC , - Further reactions Ar ~Ar 261Unauthenticated Download Date | 5/9/18 9:17 PM

Abstract. Photolysis of 6‐acetyluracil (λ>300nm) in aqueous solutions produced a single major photoproduct, arising from a singlet excited state. This photoproduct has been isolated and characterized as a novel oxetane‐type dimer.

No abstract

No abstract

Orotic acid (I) and 3-methylorotic acid (11) are the only orotic acid derivitives which efficiently sensitire emission from Eu(II1) in D 2 0 solution. This emission is only weakly sensitized by I-methylorotic acid (III), 1,3-dimethylorotic acid (IV), the methyl and isopropyl esters of orotic acid (V) 6-acetyluracil (VI) and not sensitized at all by the bases uracil. thymine and their nucleosides. Substituent groups on either the carboxyl group or the N-l position of the ring thus prevent efficient energy transfer from the excited orotic acid to Eu(1II). These structural requirements for efficient energy transfer are the same as the structural requirements for formation of a stable. bidentate. ground state complex between Eu(II1) and orotic acid (VII) (Sarpotdar and Burr, 1978).We. therefore. propose that sensitization of Eu(ll1) emission by orotic acid at pH 5 is an example of energy transfer within the bidentate complex of Eu(II1) and orotic acid. We also propose that the complexed orotic acid is itself excited by eollisional energy transfer from free triplet excited orotic acid (since the concentration of complex measured to be present. 5-7"4,, is too low to account for the efficiency of the sensitization). We also propose that emission from the excited complexed Eu(Il1) can be either from the complexed ion or from free Eu(III)* resulting from dissociation of the complex during the lifetime of the excited ion.The efficiency of Eu(lI1) sensitized emission is shown to depend on the concentrations of Eu(1II). orotic acid and pH with relationships kinetically consistent with the above hypothesis.