To get a deeper insight into the structural and electronic features of the studied fragments, DFT study of 2-methyl-3,3-difluorooxetane (15a), 2-methyloxetane (15b), 1,1-difluoro-2-methylcyclobutane (15c), and methylcyclobutane (15d) was performed. Molecular electrostatic potential (MEP) analysis was used to identify reactive sites of the corresponding fragments (Figure , C). Negative (red) and positive (blue) regions of the electrostatic potential contour maps denote the sites of possible electrophilic and nucleophilic attack, respectively. Thus, introduction of a single electron-withdrawing moiety (either O or CF2) mainly affected α-Carbon atoms, inverting their electrostatic potentials from slightly negative to neutral or positive values (compare 15d and 15b/15c). At the same time, the combination of both CF2 and O fragments in the molecule 15a had a synergistic effect, significantly decreasing the electrostatic potential on all the Carbon atoms of the four-membered ring and hence creating an X-shaped electrostatic map with opposite potential signs.