Abstract: The reaction mechanism of the homogeneous prolysis of β-propiolactone (3-oxetanone) was studied by means of ab initio SCF MO method with 3-2lG basis set. There are two possible reaction channels:
C_2H_4+CO_2(1)←CH_2—C—O—CH_2→(2)CH_2=C=O+H_2CO
The geometries of the reactant, transition states and products of (1) and (2) have been optiminzed by energy gradient technique. Second order Mφller-Plesset perturbation (MP2) calculations were carried out at the HF optimized geometries to obtain better energetics. The activation barriers are 116.0 and 302.0 kJ mol~(-1) for (1) and (2) respectively. From the results of calculations it can be seen that pyrolysis must chiefly proceed via the reaction path (1). This conclusion is in accordance with experimental observations.