Theoretical Study on the Cycloaddition of Propadiene with Ethyene

The reaction mechanism of 2+2 cycloaddition of propadiene with ethylene has been studied by semi-empirical M.O. theory AM1 method. The results show that ethylene can attack either the middle or the terminal carbon atom of propadiene. The reaction proceeds via two steps.The reactions will first pass a transition state structure and produce an intermediate, and then pass the second transition state structure to produce the product. The rate determining step is the first one, and the activation barrier is about 23 kcal/ mol, which is in accordance with experimental data.