Nitroxides bearing an alpha-hydrogen decompose upon heating in a bimolecular reaction. A new mechanism is proposed for the decomposition of t-butylisopropyl-phenyl nitroxide (TIPNO) involving the formation of a head-to-tail dimer, single electron transfer to form an oxammonium salt, epimerization to the corresponding nitrone, and elimination to form a conjugated oxime. This mechanism may provide insights into designing new nitroxides for use in controlled polymerization. (c) 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polyrn Cheni 44: 697-717, 2006