1,3-Dioxa-2,4-dimetaletanes (X = Si, Ge, Sn, Pb) are possible products from the reaction of the H2X=XH2 double bonds with dioxygen as well as from H2X=O dimerization. The energies of these reactions were investigated with DFT pseudopotential calculations (using the Becke3LYP functional and DZ+P basis sets) in order to assess the relative stabilities of X=X and X=O double bonds. While ethene and formaldehyde are exceptionally stable in this context, the reactions of most of the heavier group 14 element compounds are very exothermic. The H?X=O dimerization energy trend follows the electronegativity of X. However, the H2X=XH2 oxygenation energy decreases down group 14 from silicon to lead, and the dioxygen reaction of the trans-bent Pb2H4 minimum is even less favorable than that of of H2C=CH2. Nevertheless, Pb=Pb pi bonds are not very stable. Diplumbene can dissociate easily; reaction of the resulting divalent PbH2 subunits to tetravalent lead-oxygen compounds is not very favorable. The 1,3-dioxa-2,4-dimetaletanes have short through-ring X X distances, but no evidence for an X...X bond war found by natural bond orbital analysis. Instead, the intramolecular distances are due to the short and inflexible X-O bond lengths and to the electrostatic O ... O repulsion. In (H2XO)(2), the hybridization not only of the group 14 elements down the group but also of the oxygen lone pairs and bond orbitals changes significantly.