Direct X-ray photoelectron (XPS) and reflection-absorption infrared (RAIRS) spectroscopic evidence is reported here for the formation of a C-O bond via the thermal activation of adsorbed 2-propyl groups in the presence of chemisorbed oxygen on a Ni(100) single-crystal surface. The resulting species, 2-propoxide intermediate, was identified by a shift in binding energy of some of the C Is photoelectrons to approximately 285.3 eV and by the appearance of a C-O stretching vibrational mode in the infrared spectrum at about 1095 cm(-1). The propoxide species forms around 200 K and remains on the surface until temperatures above 300 K, at which point they undergo beta -hydride elimination to yield acetone.