The condensation of diethyl 1-oxomethylphosphonates with α-aminoglycinemethylester, α-aminoalaninemethylester, α-aminovalinemethylester, α-aminophenylalaninemethylester at room temperature in the presence of the ceaves gives the corresponding acetamides, and not the α-iminophosphonates. This study of reactivity have also explored by the theoretical study using the program GAUSSIAN 98 and hybrid B3LYP functional density with 6-31G*. Moreover, the electronic properties such as highest occupied molecular orbital (HOMO) and lowest unoccupied orbital (LUMO) energy have been investigated. Theoretical results have confirmed that the formation of the α- iminophosphonates is not favored thermodynamically, and have indicated that B3LYP/6-31g (d) model is a suitable and precise method for studying molecular structure of α-iminophosphonates.