The reactions of 9-substituted anthracene cation radicals (XA (+) (.) s) with water and methanol in acetonitrile were analyzed using an electron transfer stopped-flow (ETSF) method. By adopting the tris(2,4-dibromophenyl)amine cation radical (TDBPA (+ .)) as a reaction initiator, five XA (+ .) s, i.e. phenyl, bromo, acetyl, benzyl, and methyl derivatives, could be generated quantitatively by mixing XA with TDBPA (+ .) and the chemical reaction processes of XA (+ .) s with water or methanol (ROH) could then be followed by observing dynamic transformation processes of the absorption spectra. Consequently, the reaction orders of XA (+ .) and ROH as well as the reaction rates could be determined. The order of the reactivity was anthracene (+ .) > 9-methylanthracene (+ .) > 9-benzylanthracene (+ .) > 9-acetylanthracene (+ .), 9-bromoanthracene (+ .) > 9-phenylanthracene (+ .), and diverse changes in the reaction orders of both XA (+ .) and ROH were observed indicating some mechanistic changes. The order of the reactivity was difficult to explain only on the basis of the character of XAs or XA (+ .)s. However, as a hypothesis, it can be assumed that when the electron transfer between XA (+ .) and XA(ROH) (+ .) is favorable to formation of XA(ROH)(2+), the reaction order of [XA (+ .)] is second, and the reaction rates become faster. (C) 2003 Elsevier B.V. All rights reserved.