The allylic anions derived by proton abstraction from 2,4,4-trimethyl-1-pentene 1 and 2,4,4-trimethyl-2-pentene 2 have been studied as short-lived intermediates. The anions were generated in t-butyl alcohol-0-d-potassium t-butoxide at 21 5 "C and relative rates of hydrogen-deuterium exchange and isomerization were compared. The isomerization of the thermodynamically less stable 2 to 1 occurs through the cisallylic anion with a low 10% intramolecular component. The intermediate anion preferentially collapses to give 2 (3 to 1). Treatment. of 1 leads more frequently into the less substituted allylic anion.