Large Stabilization Effects by Intramolecular Beryllium Bonds in Ortho-Benzene Derivatives

Intramolecular interactions are shown to be key for favoring a given structure in systems with a variety of conformers. In ortho-substituted benzene derivatives including a beryllium moiety, beryllium bonds provide very large stabilizations with respect to non-bound conformers and enthalpy differences above one hundred kJ center dot mol(-1) are found in the most favorable cases, especially if the newly formed rings are five or six-membered heterocycles. These values are in general significantly larger than hydrogen bonds in 1,2-dihidroxybenzene. Conformers stabilized by a beryllium bond exhibit the typical features of this non-covalent interaction, such as the presence of a bond critical point according to the topology of the electron density, positive Laplacian values, significant geometrical distortions and strong interaction energies between the donor and acceptor quantified by using the Natural Bond Orbital approach. An isodesmic reaction scheme is used as a tool to measure the strength of the beryllium bond in these systems in terms of isodesmic energies (analogous to binding energies), interaction energies and deformation energies. This approach shows that a huge amount of energy is spent on deforming the donor-acceptor pairs to form the new rings.

Automated summary

Intramolecular interactions, particularly beryllium bonds in ortho-substituted benzene derivatives, play a crucial role in stabilizing conformers with newly formed five or six-membered heterocycles. The strength of the beryllium bond is quantified using Natural Bond Orbital approach, showing significant interaction energies between the donor and acceptor. Energy is mostly spent on deforming donor-acceptor pairs to form new rings in these systems.