X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, and temperature-programmed reaction/desorption have been employed to investigate the adsorption and reaction pathways of CH2=CHCOOH and CH3CHFCOOH on Cu(100) and oxygen-precovered Cu(100) [O/Cu(100)]. In the case of CH2=CHCOOH on O/Cu(100), CH2=CHCOO is the surface intermediate detected between 110 K and 400 K. CH2=CHCOO is adsorbed vertically and can change adsorption sites at a higher temperature. The propenoate (acrylate) decomposes at higher temperatures (>500 K), with formation of >C=C=O (ketenylidene) surface species and gaseous products. On Cu(100), CH2=CHCOOH is adsorbed in dimer form and can dissociate to generate CH2=CHCOO and CH3CHCOO intermediates on the surface. The CH3CHCOO continuously recombines with the H from deprotonation of CH2=CHCOOH, resulting in the formation CH3CH2COO. The co-existing CH2=CHCOO and CH3CH2COO further decompose at ∼550 K to evolve reaction products, but without >C=C=O being detected. On O/Cu(100), CH3CHFCOOH readily deprotonates to form CH3CHFCOO at 120 K. This intermediate reacts on the surface at ∼460 K to evolve gaseous products, also producing CH2=CHCOO. In the case of Cu(100), deprotonation of CH3CHFCOOH occurs at ∼250 K, forming CH3CHFCOO. Without oxygen on the surface, this intermediate decomposes into HF and CH2=CHCOO at ∼455 K.