In the gas phase, the unimolecular reaction of the metastable beta-distonic ion 1, CH3CH2OH+CH2CH2., yields a CH3CHOH+ fragment ion. Experiments using isotopomers of 1 and at, initio calculations show that two pathways lead to its dissociation : (i) a 1,4-H migration leading to the a-distonic ion 2, (CH3CHOH+CH2)-O-.-CH3, with subsequent elimination of C2H5.; (ii) a Il transfer within a [C2H5OH, C2H4](.+) intermediate complex 3 followed by loss of C2H5.. Two isomerization processes can occur prior to dissociation : a rapid permutation of the CH2 groups in the radical chain and a reversible 1,5-H migration. The calculated transition state for 1,5-H migration and those arising on the fragmentation pathways are close in energy and correspond to relatively ;high energy barriers (93-100 kJ/mol), in agreement with the isotope effects observed. Finally, the bimolecular reactions of 1 with several neutral molecules are Shown to be accompanied by the same 1,4- and 1,5-H migrations. The structures of the different isomeric ions thus formed were characterized by their specific ion-molecule reactions. The energy required for the various processes observed arises from the stabilization in the initial encounter complexes between 1 and each neutral molecule.