Effect of Methyl Substitution on the Thermochemistry of Ketene

The heats of formation of ketene, methylketene, and dimethylketene have been measured by energy-selected electron-induced dissociation of phenyl acetate, propanoate, and isobutyrate, respectively. The values are Δf H°[CH2CO] = −54 ± 5 kJ mol-1, Δf H°[CH3CHCO] = −95 ± 5 kJ mol-1, and Δf H°[(CH3)2CCO] = −137 ± 5 kJ mol-1. For ketene, the new result was in excellent agreement with literature data and recent high-level ab initio calculations. …