A quantum chemical investigation of pyrolysis reactions of glyoxylic acid ethylester

Two possible reaction paths for the pyrolysis of the ethylester of glyoxylic acid have been studied by ab initio molecular orbital calculations. The basis sets 3‐21 G and 6‐31 G * have been used, and electron correlation has been included by Møller–Plesset calculations up to fourth order. Our calculations indicate that the reaction leading to acid and ethylene through a 6‐membered ring transition state is favored relative to a process involving a formyl hydrogen transfer via a 5‐membered ring to the alkyl unit leading to ethane, CO, and CO 2 . The predicted activation energies for these two reactions obtained at the highest level of calculation, MP 4( SDTQ )/6–31 G *, are 50.4 and 71.7 kcal/mol, respectively. The transition states have RHF wave functions that are stable relative to UHF solutions using the 3–21 G basis. The geometry of the transition states and IRC following indicate that both reactions are strongly asynchronous: The CO bond rupture is virtually completed before hydrogen transfer occurs. For comparative purposes, analogous calculations have been performed for the ethylester of formic acid, where it is confirmed that a 6‐membered ring transition state is preferred relative to a 4‐membered one by around 42 kcal/mol at the highest level of calculation.