2-Hydroxy-2-propyl radical reacts with highly different rate coefficients (k) with the three protonation forms of maleic and fumaric acids. With protonated fumaric acid k is high, (2.1 +/- 0.4) x 10(9) mol(-1) dm(3) s-(1) due to the nucleophilic character of IP reaction and the electron withdrawing -COOH groups. With mono- and dianion molecules the k's are smaller, (6.6 +/- 0.7) x 10(8) and (3.1 +/- 3.0) x 107 mol(-1) dm(3) S-1. In maleic acid k for the monoanion is higher ((1. 34 +/- 0.03) x 10(9) mol(-1) dm(3) s(-1)) than for protonated and dianion species, (5.6 +/- 0.6) x 10(8) and (3.5 +/- 3.1) X 10(7) mol(-1) dm(3) s(-1). The high k is interpreted in terms of cyclic structure and charge localization between carboxylic groups. (c) 2007 Elsevier B.V. All rights reserved.