Electron spin resonance investigator of the 5-halouracil and 5-halocytosine. pi. -cations produced by attack of the Cl/sub 2//sup -/ radical

Journal Article · Mon Apr 12 04:00:00 EST 1982 · J. Phys. Chem.; (United States)

OSTI ID:6563091

Sevilla, M D; Swarts, S; Riederer, H; Huettermann, J

The ..pi..-cation radicals of a number of 5-halopyrimidines have been produced by attack of the one-electron oxidizing agent, Cl/sub 2//sup -/, n ..gamma..-irradiated basic 12 M LiCl glasses at low temperatures. Analysis of the ESR spectra for the ..pi..-cations was completed with the inclusion of nuclear quadrupole terms for Cl, Br, and I, in addition to the hyperfine and g tensors. The halopyrimidines investigated were 5-fluorouracil, 5-chlorouracil, 5-bromouracil, 5-iodouracil, 5-fluorocytosine, and 5-bromocytosine. The results for the halouracil ..pi..-cations are found to be in agreement with previous results found for the N-1 deprotonated cations identified in single crystals and acid glasses. The halocytosine ..pi..-cations gave evidence for a further reaction after production by Cl/sub 2//sup -/ attack. Both the 5-fluorocytosine and 5-fluorouracil ..pi..-cation radicals show large fluorine couplings (A/sub zz/ = 150 G) and a single nitrogen coupling (A/sub zz/ = 13 G) at low temperatures. However, in the case of 5-fluorocytosine warming results in the conversion of the original ..pi..-cation to a new species whose fluorine splitting decreases dramatically to 115 G while two nitrogen splittings are found of nearly equal magnitude (A/sub zz/ = 16 G). These results are shown to be excellent evidence that deprotonation of the exocyclic nitrogen has taken place. Similar results are found with 5-bromocytosine. The reduction of the halogen splitting after deprotonation of the exocyclic nitrogen in 5-fluorocytosine and 5-bromocytosine is suggested to be a result of increased delocalization of the unpaired spin onto the exocyclic nitrogen. This is supported by INDO-MO calculations for the protonated and unprotonated structures.

• Research Organization: Oakland Univ., Rochester, MI
• OSTI ID: 6563091
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 88:8; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400301* -- Organic Chemistry-- Chemical & Physicochemical Properties-- (-1987)
ALKALI METAL COMPOUNDS
AZINES
CHARGED PARTICLES
CHEMICAL REACTIONS
CHLORIDES
CHLORINE COMPOUNDS
CHLORINE IONS
DATA
ELECTROMAGNETIC RADIATION
ELECTRON SPIN RESONANCE
EXPERIMENTAL DATA
GAMMA RADIATION
GLASS
HALIDES
HALOGEN COMPOUNDS
HETEROCYCLIC COMPOUNDS
INFORMATION
IONIZING RADIATIONS
IONS
LITHIUM CHLORIDES
LITHIUM COMPOUNDS
LITHIUM HALIDES
MAGNETIC RESONANCE
MOLECULAR STRUCTURE
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PYRIMIDINES
RADIATIONS
RESONANCE