ESR and proton ENDOR studies in urea oxalic acid (2:1) single crystal: Radical transformation

A radical transformation has been investigated in a single crystal of urea oxalic acid (2:1) irradiated at room temperature. ENDOR studies (∼−160 °C) have been performed on both the initial and final radicals. The initial species has been assigned to a protonated anion radical. The results indicated that a common proton was involved in the protonation of the anion and in the subsequent transformation to R–ĊHOH. Two important differences in relation to the earlier studies on the protonated anions were noted. The maximum dipolar coupling values (Bmax) for the O–Hβ protons are smaller than normal and the proton transfer is not across the hydrogen bridge. A qualitative estimation of the spin densities indicated delocalization and the possible causes for small values of Bmax are discussed. A mechanism proposed earlier is invoked to understand the radical transformation.

[1]  T. Rao,et al.  CO2− radical in γ-irradiated single crystal of calcium formate: reinvestigation , 1981 .

[2]  T. Rao,et al.  Studies of radicals in oxalate systems , 1980 .

[3]  H. Box,et al.  Exchangeable proton couplings in free radicals: Radiation products of hydroxyproline HCl , 1978 .

[4]  W. Bernhard,et al.  Radiation Effects: ESR and ENDOR Analysis , 1977 .

[5]  J. Hüttermann,et al.  ESR and ENDOR of free radicals in X-irradiated barbituric acid , 1976 .

[6]  L. Kevan,et al.  Electron spin double resonance spectroscopy , 1976 .

[7]  M. Iwasaki,et al.  ENDOR studies of the superhyperfine couplings of hydrogen‐bonded protons. IV. Carboxyl radical anions in irradiated glycine and α‐amino isobutyric acid , 1974 .

[8]  K. Nunome,et al.  ENDOR studies of the superhyperfine couplings of hydrogen-bonded protons. III. Protonated radical anions in irradiated l-valine hydrochloride monohydrate , 1974 .

[9]  K. Nunome,et al.  ENDOR studies of the superhyperfine couplings of hydrogen bonded protons. II. Protonated radical anion in irradiated succinic acid single crystals , 1974 .

[10]  M. B. Yim,et al.  ESR study of 13C hyperfine splittings for the single line radical produced in γ‐irradiated single crystals of succinic acid , 1974 .

[11]  O. Edlund,et al.  ENDOR study of γ-irradiated single crystals of sodium hydrogen oxalate monohydrate, NaHC2O4·H2O , 1973 .

[12]  R. Rudman,et al.  The formation of the plastic crystal phase in several pentaerythritol derivatives , 1973 .

[13]  C. Poole,et al.  Solving the Spin Hamiltonian for the Electron Spin Resonance of Irradiated Organic Single Crystals , 1971 .

[14]  E. Gabe,et al.  The crystal structure of anhydrous lithium glycolate, 6Li-(s)-glycolate-2d. , 1966, Acta crystallographica.

[15]  D. Whiffen,et al.  Hyperfine coupling in containing radicals , 1964 .

[16]  W. Derbyshire.  The coupling between an unpaired electron spin and a proton two bonds away , 1962 .

[17]  W. Gordy,et al.  DUKE MICROWAVE LABORATORY REPORT NO. 33, APRIL 1, 1961-JUNE 30, 1961. Includes papers: ELECTRON SPIN RESONANCE INVESTIGATIONS OF THE PROTEINS. ELECTRON SPIN RESONANCE OF AN IRRADIATED SINGLE CRYSTAL OF UREA OXALATE , 1961 .

[18]  D. Whiffen,et al.  Electron spin resonance of ?-irradiated malonic acid , 1961 .

[19]  D. Whiffen,et al.  Conformational isomerism in the HĊ(OH)CO–2 radical ion , 1961 .

[20]  D. Whiffen,et al.  An electron spin resonance study of a γ-irradiated single crystal of glycollic acid , 1960 .