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Effect of pH on muonium reactions in aqueous solutions of p-aminobenzoic acid

TitleEffect of pH on muonium reactions in aqueous solutions of p-aminobenzoic acid
Publication TypeJournal Article
Year of Publication1996
AuthorsVenkateswaran, K, Stadlbauer, JM, Wu, ZN, Gillis, HA, Walker, DC
JournalJournal of Physical Chemistry
Volume100
Pagination3569-3572
Date PublishedFeb
Type of ArticleArticle
ISBN Number0022-3654
KeywordsADDITION-REACTIONS, electron, ENERGY, HYDROGEN, LEVEL-CROSSING-RESONANCE, ORGANIC FREE-RADICALS, SPECTROSCOPY, SPIN ROTATION
Abstract

p-Aminobenzoic acid was studied as a solute in water to determine the effect of altering the pH from 1 to 10 on the rate of reaction and on the site of addition of muonium atoms. This solute exists in three different acid-base states ranging from the fully protonated, through neutral, to anionic, and its substituents change from electron-accepters to electron-donors with increasing pH. The overall rate of reaction is barely affected by pH, but there is nearly a 2-fold switch in the site at which muonium adds to the ring. There is also a considerable switch in the magnetic field at which muon level crossing resonance occurs, the radical with muonium attached at C(2) moving upfield by 125 mT and the C(3) one moving downfield by a similar amount. If this compound is representative of aromatic systems, then the differences in pH which usually exist between hydrogen and muonium studies would account for only a small factor in most reported kinetic isotope effects.

URL<Go to ISI>://A1996TX76600039