For many years we have sought computational support for the bent bond/antiperiplanar hypothesis (BBAH). The concept of geminals1 (two-electron orbitals) in quantum chemistry addresses many of the inherent issues stemming from the one-electron formalism that is Hartree-Fock theory. Geminals offer a close connection to the valence bond model that is so familiar to organic chemists.
APSG (antisymmetry product of strongly orthogonal geminals) calculations were recently carried out on the allyl anion as an initial test case for the computational support of the BBAH. We are grateful for these preliminary results obtained by Prof. Patrick Cassam-Chenai2 (U. Côte D’Azur), which reveal clear bent geminals for the C=C component of the allyl anion! The following orbitals were generated by the APSG/ccpVDZ protocol and visualized with IQmol3:
The two tau orbitals appear as geminals #10 and #11. In its planar molecular geometry, the allylic geminal (#12) is symmetric. How the lone pair of geminal #12 delocalizes into the bent geminals needs to be established. How the geminals change shape as the allylic carbon becomes pyramidal needs to be determined. According to the BBAH, a non-symmetric allylic anion (or radical) should delocalize into the antiperiplanar bent bond:
- Surjan, P. R. An introduction to the theory of geminals. Topics in current chemistry 203, 64–77 (1999).
- https://univ-cotedazur.fr/patrick-cassam-chenai
- http://www.iqmol.org
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