The influence of several substituents on the ring-opening elementary step of cyclobutene-like systems is analyzed computationally in details. We focus on trans-1,2-disiloxycyclobutene-like molecules. Electronic effects (hyperconjugation and [small pi] delocalization) and geometrical constraints are decoupled and allow for an instructive analysis. It is found that the energy difference between closed and open forms are dictated mainly by the electronic structure of the open form, in which the rotation along the resulting simple C-C bond drives the electronic delocalization. Our calculations lead us to quantify effects that determine the energy difference in the special case of disubstituted benzocyclobutene with respect to the disubstituted o-xylylene (aromaticity, [small pi] delocalization, ring strain). The relevant role of the siloxo-substituents is rationalized by an analysis of the molecular orbital interaction in an original manner. Finally, calculations are presented and show that the PBE0 functional must be preferred to the popular B3LYP functional for computations on substituted cyclobutene-like rings.