The bonding properties and the potential energy surfaces for the chemical reactions of doubly bonded compounds that have the >E-13-E-15< pattern are studied using density functional theory (M06-2X/Def2-SVPD). Nine molecules, >E-13-P< (E-13 = B, Al, Ga, In, and Tl) and >B-E-15< (E-15 = N, P, As, Sb, and Bi), are used as model reactants in this work. Four types of chemical reactions, H2 addition, acetonitrile, benzophenone [2 + 2] cycloadditions, and dimethylbutadiene [4 + 2] cycloaddition, are used to study the chemical reactivity of these inorganic, ethylene-like molecules. The results of these theoretical analyses show that only the >B=P< molecule has a weak B-P double bond, while the >Al=P< , >Ga=P< , >In=P< , >Tl=P< , >B=N< , >B=As<, >B=Sb<, and >B-Bi< compounds are best described as having a strong single s bond, instead of a traditional p-p p bond. The theoretical results also show that the singlet-triplet energy gap can be used to determine the relative reactivity of these doubly bonded molecules. According to these theoretical investigations, it is predicted that the order of reactivity is as follows: B-P > Al-P > Ga-P > In-P > Tl-P and B-N<< B=P < B-As < B=Sb < B=Bi. The conclusions drawn are consistent with the available experimental observations.