40680-12-4Relevant academic research and scientific papers
13C HYPERFINE INTERACTIONS IN TEREPHTHALATE TRIANION RADICAL
Qin, Ling,Madden, Keith P.,Schuler, Robert H.
, p. 3790 - 3792 (1988)
Sufficiently high concentrations of terephthalate radical trianion can be produced by reduction of terephthalate with acetone ketyl radical anion in in situ radiolysis experiments that ESR spectra of the radicals containing 13C at natural abundance levels can be recorded readily.The 13C hyperfine constant for the carbon atoms at the four equivalent ring positions is (-)1.46 G.Hyperfine constants of 1.37 and 4.64 G are observed for the other two pairs of equivalent carbon atoms with the smaller value found to apply to the carboxylcarbons from studies of a sample with the carboxyl group enriched in 13C.Application of the Karplus-Fraenkel relation indicates that there is an unpaired spin population of 0.26 on each of the ring carbon atoms adjacent to the carboxyl groups.This high-spin population is reflected in somewhat broadened lines of the radicals with 13C at these ring positions.The signals of this radical saturate relatively easily, indicating a longitudinal relaxation period considerably longer than for most transient radicals.
ESR study of the photochemistry of benzole acid derivatives
Jeevarajan,Fessenden, Richard W.
, p. 10461 - 10470 (2007/10/02)
Electron spin resonance (ESR) has been used to study radical intermediates in the photochemistry of a number of aromatic carboxylic acids, esters, anhydrides, amides, imides, and nitriles. Continuous photolysis was used to produce the radicals in either aqueous or alcoholic media. The triplet states of the compounds undergo two reactions in the presence of a hydrogen donor such as 2-propanol. A hydrogen atom is transferred to certain carbon atoms of the aromatic ring forming cyclohexadienyl radicals. In most cases, addition occurs at or opposite the carboxyl (or cyano) group. The pattern of addition is attributed to the higher spin density in the triplet at those positions. This pattern also correlates with the positions of higher hyperfine splitting in the corresponding anion radicals. In a parallel reaction, a hydrogen atom is also transferred to an oxygen of the carboxyl group (for acids, anhydrides, and esters) to form the one-electron-reduction product. The cyclohexadienyl radicals are not formed by protonation on a carbon of an anion radical. The ESR spectra of most of the cyclohexadienyl radicals are highly polarized to the extent that the low-field lines appear in emission. This effect is believed to be normal chemically induced dynamic spin polarization (CIDEP) as a result of cross reactions with the other radicals present.
