Thermal Stability of Larger Carbonyl Compounds: 2‐Methylbutyraldehyde

We have decomposed 2‐methylbutyraldehye in single pulse shock tube experiments, at temperatures between 1075 K to 1250 K and pressures of 1.5 and 6 atm. Five reaction channels have been identified from the unimolecular products that have been detected. The products involve CC bond cleavage together with a retro‐ene reaction. Particularly remarkable is the detection of small amount of butane; the first time that an alkane has been detected in these high‐temperature experiments. The formation of butane represents evidence of the roaming radical reaction or more generally the high‐temperature radical disproportionation reaction. Ethylene is present in large yields, and this is traced to a 1,2 H‐transfer reaction involving the highly exothermic transfer of a carbonyl hydrogen to an alkyl site. The results are consistent with earlier single pulse shock tube experiments on the 2‐ketones. In particular, they confirm the earlier observation that substituting a methyl and hydrogen atom with a doubly bonded oxygen atom have very little effect on the rate constant of the adjoining CC bond. The yields of ethylene are consistent with a very low value of the carbonyl resonance energy.