The potential energy surfaces corresponding to the reaction of cyclic, unsaturated diaminocarbene (DAC), -silylene (DAS), and -germylene (DAG) with methane have been investigated by employing the B3LYP and CCSD(T) levels of theory. Our model calculations demonstrate that the electronic perturbation effect should play a significant role in determining the magnitude of their singlet-triplet splitting. Namely, the singlet-triplet gap of DAC, DAS, and DAG shows the opposite order as the parent compounds (CH2 SiH2, and GeH2), as well as the compounds with pi-donor substituents (C(NH2)(2), Si(NH2)(2), and Ge(NH2)(2)). Our theoretical investigations suggest that the heavier the X center (X = C, Si, Ge), the larger the insertion barrier, and the less exothermic (or the more endothermic) the insertion reaction. Namely, the chemical reactivity decreases in the order DAC, DAS > DAG. Even so, all the species are predicted to be kinetically stable with respect to insertion reactions with alkanes. Moreover, it is found that a singlet state DAC, DAS, or DAG inserts in a concerted manner, and that the stereochemistry at the X center (X = C, Si, and Ge) is preserved.