Electron spin resonance study on the acrylic acid anion radical and its protonation in some irradiated frozen solutions

Abstract

An esr study has been carried out for reactions of electrons with acrylic acid (AA) in a variety of irradiated frozen solutions. The electron adducts of acrylic acid [CEL-CH-COOH]" were found to be formed in some matrices, such as 2-methyltetrahydrofuran (MTHF), triethylamine (TEA), and 3-methylhexane (MHX). The hyperfine couplings to the end CH2 protons (oq 13 G) are consistent with the INDO MO calculation made for the delocalized anion w radical. The post-irradiation thermal annealing of the frozen MTHF-AA solutions at 97°K resulted in protonation of the electron adducts to form the hydrogen addition radical [CH3-CH-COOH]. The same conversion was also observed in the TEA matrices at around 115°K, while no conversion was observed in the MHX matrices. The radical conversion seems to be associated with the molecular reorientations in the matrices which were found from the sudden change of the line width in the wide-line nmr measurements of frozen MTHF. On the other hand, the hydrogen addition radicals were found immediately after irradiation in some matrices containing polar protons such as alcohols and alkaline aqueous solutions. It is concluded that the electron adducts of acrylic acid can be stabilized either in a molecular anion or in its protonated form, depending upon the nature of the matrix molecules and that the hydrogen addition radicals are formed from the polar proton transfer to the electron adducts. A model of proton transfer from protonated cations via the hydrogen bond is proposed for protonation of the electron adducts in the MTHF and TEA matrices.

Radical formation in electron-irradiated acrylates studied by pulse radiolysis and electron paramagnetic resonance

“…4 b. A superposition of the seven-line MTHF radical and a triplet assigned to the TPGDA radical anion is observed. The hyperfine coupling constants derived [7] for the TPGDA radical anion (see Tab. 2) are similar to those given by Iwasaki [16] for the anion of acrylic acid. From the triplet structure of the EPR spectrum, resulting from isotropic coupling of two protons, it is concluded that the TPGDA radical anion is a p-radical exhibiting the resonance structures (8).…”

Electron adducts of acrylic acid and homologs. Spectra, kinetics, and protonation reactions. A pulse-radiolytic study

“…Reaction 9 was observed in this work only with cinnamic acid. The rate of reaction 10 OH-r2ccrco2h-->-R2CHCRC02- (10) or buffer with all the other monoprotonated radicals is very high. Hence equilibrium 9 cannot be achieved.…”

Electron spin resonance study of radiation-induced radicals from maleic anhydride in irradiated frozen solutions

“…2 Irradiation and ESR measurements were carried out in a manner similar to those described in our previous paper. 1 The signals of Mn2+ and DPPH were used as a marker for the magnetic field as well as for the spectral intensity standard. Irradiation by uv light was made with a high-pressure mercury lamp (Ushio 500W) at 77 K. The line shape analyses and the INDO MO calculations were made using a Facom 270-30 computer.…”