ISSN:
1572-9001
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Electronic absorption and fluorescence emission spectra of several biologically important pyrimidines were measured at room temperature (298 K) in the following solvents: dioxane, ethyl ether, chloroform, ethyl acetate, 1-butanol, 2-propanol, methanol, dimethylformamide, acetonitrile, and dimethyl sulfoxide. The compounds studied were uracil, thymine, cytosine, 5-fluorouracil, 5-chlorouracil, 5-bromouracil, 5-iodouracil, 2-thiouracil, barbituric acid, and orotic acid. In combination with the ground-state dipole moments of the above compounds, these spectral data were used to determine their lowest excited singlet-state dipole moments using the soivatochromic method. The effects of the solvent upon the spectral properties and of the structure upon the ground and excited singlet-state dipole moments are discussed. For most of the compounds, the excited singlet-state dipole moments are higher than their ground-state counterparts. The theoretical dipole moments for all the pyrimidines listed above, as well as for pyrimidine, alloxan, and uracil-5-carboxylic acid, were calculated by two methods. One approach involved a combination of the PPP (π-LCI-SCF-MO) method for the π-contribution to the overall dipole moment and the σ-contribution obtained as a vector sum of the σ-bond moments and group moments. The second set of theoretical values was obtained by the CNDO/2 method. The results were compared with the experimental dipole moments.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00672795
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