Resonance Raman studies of substituent effects on the electronic structure of phenoxyl radicals

Journal Article · Thu Sep 08 00:00:00 EDT 1988 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100329a015· OSTI ID:6254985

Tripathi, G N.R.; Schuler, R H

The resonance Raman spectra of para-substituted phenoxyl radicals (XC/sub 6/H/sub 4/O/center dot/; X = CH/sub 3/, F, Cl, Br, OCH/sub 3/, OH) observed by time-resolved techniques in aqueous medium, exhibit a wide variation in spectral features intermediate between phenoxyl and /rho/-benzosemiquinone anion radicals. The ..nu../sub 7a/ (CO stretch) vibration, which is strongly enhanced on Raman excitation in resonance with the electronic transition in the approx. 400-nm region, appears in a narrow frequency range 1511-1518 cm/sup /minus/1/, indicating that the CO bond in the ground electronic state of these radicals is very similar to that of phenoxyl (..nu../sub 7a/ at 1505 cm/sup /minus/1/). The relative intensities of the ..nu../sub 8a/ bands (CC stretch), observed in the 1552-1613-cm/sup /minus/1/ region, change dramatically with the electronic properties of the substituent group. This vibration, which is not apparent in the Raman spectrum of phenoxyl excited at 400 nm, is observed with an intensity comparable to the of the ..nu../sub 7a/ vibration in the /rho/-bromo, /rho/-methoxy, and /rho/-hydroxy derivatives. The Raman intensities show that the electronic structures in the excited states of the /rho/-methoxy and /rho/-fluoro-, and p-chloro-substituted radicals are essentially phenoxyl like, while the structures in p-methoxy and p-hydroxy derivatives approach that of /rho/-benzosemiquinone anion radical as a result of strong interaction of the substituent's p..pi.. electrons with the phenoxyl ..pi.. system. The excited state of /rho/-bromophenoxyl radical represents an important intermediate case. The resonance enhancement of the ..nu../sub 9a/ CH bending vibration, observed at approx. 1160 cm/sup /minus/1/, parallels that of the ..nu../sub 8a/ phenyl mode and provides an important diagnostic for assignment of the latter vibration.

• Research Organization: Univ. of Notre Dame, IN (USA)
• OSTI ID: 6254985
• Journal Information: J. Phys. Chem.; (United States), Vol. 92:18
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
HYDROXY COMPOUNDS
ELECTRONIC STRUCTURE
ORGANIC BROMINE COMPOUNDS
ORGANIC CHLORINE COMPOUNDS
ORGANIC FLUORINE COMPOUNDS
PHENOXY RADICALS
EXPERIMENTAL DATA
NORMAL-MODE ANALYSIS
RAMAN SPECTRA
RAMAN SPECTROSCOPY
RESONANCE SCATTERING
VIBRATIONAL STATES
DATA
ENERGY LEVELS
EXCITED STATES
INELASTIC SCATTERING
INFORMATION
LASER SPECTROSCOPY
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
RADICALS
SCATTERING
SPECTRA
SPECTROSCOPY
400201* - Chemical & Physicochemical Properties