Decomposition of activation barrier of the Aza-Diels-Alder in the presence of PHX2 (X=F, Cl, Br)

The effect of PHX2 (X=F, Cl, Br) on the activation barriers of H2C=NNH2 (dienophile) and 1,3-butadiene(diene) cycloaddition has been explored by means of density functional theory (DFT) and energy decompositionanalysis (EDA). For these cycloadditions, the activation barriers were investigated using activation strain model anddecomposition of the activation barrier into orbital interaction, electrostatic interaction, paulirepulsion and distortion energy was reported. Also, the relationship between interaction energies anddistortion energies of transition states these cycloadditions were investigated. The results show that in the presence ofPHX2 (X= F, Cl, Br), distortion energy of diene and dienophile decreased and also the interaction energies betweenreactants increased. Therefore, in presence of PHX2 (X= F, Cl, Br), activation barrier for this cycloaddition decreased.