PUB - Publikationen an der Universität Bielefeld

A novel fragmentation reaction accompanied by the unidirectional migration of three hydrogen atoms has been found in the radical cations of -arylpropanols with electron-donating substituents in the para position. This triple hydrogen (3H) rearrangement reaction is the dominant fragmentation channel of the long-lived molecular ions of trans-2-(4-dimethylaminobenzyl)-l-indanol, 2, but it occurs also in simpler -arylpropanol ions. Deuterium labelling of 2 reveals that the three hydrogen atoms originate with extraordinarily high specificity from the C(l), C(2) and O positions of the alcohol moiety. Cis- and 3-substituted isomers do not undergo this reaction. Along with the 3H rearrangement reaction a unidirectional double hydrogen (2H) rearrangement reaction takes place independently and with less specificity in the trans-2-(4-X-benzyl)-l-indanol ions 1+· and 2+·. No hydrogen exchange occurs during the 3H and 2H rearrangement reactions. Mechanistic alternatives of these unusual fragmentation reactions are discussed; the experimental evidence strongly favours pathways via several intermediate ion-neutral complexes.