The free-radical addition reaction of malonic ester with a series of alkenes under the uniform conditions has been studied.The relationship between the yields and the structure of the alkenes,as expressed in teems of the inductive indices for the substituent groups on the ethylenic bond,has been found to be a reversed sigmoid ("S-") curve.It indicates that this addition reaction is an electrophilic free-radical addition of the malonic ester radical,·CH(COOC₂H₅)₂,to the alkene molecules.