Resonance Raman studies of pulse radiolytically produced p-aminophenoxyl radical
The p-aminophenoxyl radical produced in the pulse radiolytic oxidation of p-aminophenol in aqueous solution has been examined by time-resolved resonance Raman methods. Eight Raman bands of fundamental vibrations were observed at microsecond times and at radical concentrations of -- 10/sup -5/M by excitation in the moderately strong absorption band of this radical at 444 nm (E = 6800 M/sup -1/ cm/sup -1/). This radical decays rapidly by second-order processes (2k = 2 x 10/sup 9/ M/sup -1/ s/sup -1/) so that at times longer than milliseconds the residual signals are very weak. The most intense Raman band of this radical, observed at 1636 cm/sup -1/, is ascribed to the Wilson 8a ring stretching mode and is similar in frequency to this mode in p-benzosemiquinone radical anion (1620 cm/sup -1/). The mixed CO/CN stretching frequency (1434 cm/sup -1/) is also very similar to that of the analogous mode in p-benzosemiquinone. This radical exhibits no strong Raman bands in the region of 1510-1520 cm/sup -1/ as do most other substituted phenoxyl radicals. Deuterium substitution of the NH/sub 2/ group shows that a band at 1673 cm/sup -1/ in the protonated radical is due to the symmetrical NH/sub 2/ bending vibration. Interestingly, this deuterium substitution results in small increases in the frequencies of the CO/CN and ring stretching vibrations. The Raman data show very clearly, in agreement with conclusions from ESR data, that the structure of p-aminophenoxyl radical is more similar to that of a semiquinone than it is that of a phenoxyl radical. The high second-order rate constant observed for decay, however, indicates that the NH/sub 2/ group contributes significantly to modifying the redox properties of this radical.
- Research Organization:
- Univ. of Notre Dame, IN
- OSTI ID:
- 6454382
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 88:9
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AQUEOUS SOLUTIONS
CHEMICAL RADIATION EFFECTS
RAMAN EFFECT
DEUTERIUM
ISOTOPE EFFECTS
ELECTRONS
PHENOLS
EXPERIMENTAL DATA
PULSED IRRADIATION
RAMAN SPECTRA
AROMATICS
CHEMISTRY
DATA
DISPERSIONS
ELEMENTARY PARTICLES
FERMIONS
HYDROGEN ISOTOPES
HYDROXY COMPOUNDS
INFORMATION
IRRADIATION
ISOTOPES
LEPTONS
LIGHT NUCLEI
MIXTURES
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
RADIATION CHEMISTRY
RADIATION EFFECTS
SOLUTIONS
SPECTRA
STABLE ISOTOPES
400600* - Radiation Chemistry
400302 - Organic Chemistry- Isotope Effects- (-1987)