This work aims to clarify preferred chemical routes in an autothermal system by investigating individually two-carbon molecules containing the functional groups found in bio-oil. In part 2, conversion and selectivity to major compounds are compared in the presence and absence of alpha-Al2O3 support and oxygen. Oxygen significantly increases conversion, even at feed rates insufficient to sustain autothermal operation. In general, below 450 degrees C, homogeneous reactions in the absence of oxygen are insignificant for all molecules; in the presence of oxygen, the reaction onset temperature is somewhat lower. The role of the alpha-Al2O3 support appears to be a combination of improved heat transfer and the radical quenching ability of the foam structure. Acid catalysis appears minor compared to these other functions. With no O-2 co-feed, acids, ethers, and aldehydes appear to be more stable than alcohols and esters. With O-2, co-feed, acids and ethers may be less reactive in the gas phase than the other functionalities studied. Implications for autothermal systems are discussed.