Uracil spectral data

Spectral data (Amax and AE, and e x 10 3) for the pyrimidine bases investigated in a few representative papers are collected in Table XXVIII. The absorption bands are denoted by the capital letters A, B, C, etc. In Table XXVIII we have listed the results of the vacuum ultraviolet measurements by Yamada and Fukutome428 (cf. also ref. 429), who measured the spectra of sublimed films of cytosine, thymine, uracil (and also of guanine and adenine) down to 120 nm at room temperature. Several remarkable absorption peaks were found below 190 nm in addition to the already known ones near 260 and 200 nm. A weak absorption at 230-240 nm in cytosine was not indicated in the sublimed films of the molecule,428 but was visible in the stretched polyvinyl alcohol film spectrum.432 Crewe et al.i3° studied the interactions of fast electrons with the five nucleic acid bases and measured the energy-loss spectra of 20 keV electrons transmitted through thin films of these bases. These last data are also listed in Table XXVIII for comparison with the other spectral findings. 

Near- and Far-UV Spectral Data for Cytosine, Uracil, and Thymine... 

Hydrolysis of 63 in concentrated hydrochloric acid at 100 °C for 6 h afforded 95% of uracil diol 65 with H and 13C NMR spectral data virtually identical to those of cylindrospermopsin except for the protons and carbons close to C12. A similar hydrolysis of 64 provided 95% of 66. This hydrolysis is perhaps the most remarkable step in the synthesis. Very harsh conditions are needed to hydrolyze the dimethoxypyrimidine to the uracil. However, the reaction is remarkably clean, accompanied only by the desired hydrolysis of the acetate ester, but no decomposition or epimerization at any of the stereocenters. Presumably, the protonated guanidine and uracil make it hard to protonate either alcohol and solvolyze to form a trication. 

The formation of a solid, isolated by bubbling fluorine diluted with nitrogen into a solution of pyridine in trichlorofluoromethane at — 80 °C followed by filtering at low temperature, has been noted.30 The solid is considered to be a pyridine/fluorine compound with polar character however, spectral or other data on the structure of the pyridine/fluorine compound are presently not available, probably due to its explosive nature. This compound has been used for the fluorination of uracil and some chloroalkenes,30,31 but the adduct is of little use because of its violent decomposition above — 2CC. 

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