Valence Bond Theory and Electronic Structure in Chemistry

Valence bond theory offers a description of chemical bonding in which atomic orbitals overlap to form localized electron pairs, blending ionic and covalent contributions to yield resonance energies that stabilise molecules. Developed alongside molecular orbital theory, which treats electrons as delocalised across an entire molecule, valence bond theory emphasises the pairing and spin coupling of electrons, capturing essential aspects of bond formation, reactivity and magnetic properties. Advances in computational methods now permit rigorous treatment of electron correlation directly within a valence bond framework, revealing real-space patterns of bonding and resonance without reliance on orbital approximations. Electronic structure broadly encompasses the arrangement, energy and interactions of electrons within atoms and molecules. Core concepts include electron delocalisation, where electrons are shared over multiple centres; resonance, the stabilisation from the mixing of alternative Lewis structures; and aromaticity, a form of cyclic delocalisation governed by electron count rules. Together, these ideas underpin our understanding of bond strengths, reaction pathways and the functional properties of organic, inorganic and biological systems.

Research from Nature Portfolio

Recent studies have partitioned the full many-electron wavefunction of benzene into symmetry-related regions, or “tiles,” to map directly onto classical resonance structures. By projecting these regions into three-dimensional real space, researchers have visualised the superposition of Kekulé forms and demonstrated that opposite-spin electrons preferentially occupy alternate resonance structures. This work provides a succinct, wavefunction-based picture of electron correlation in benzene and clarifies how spatial avoidance of like-spin electrons contributes to aromatic stability.

A complementary investigation has redefined delocalisation, resonance and aromaticity from first principles in real space, using probability density pathways rather than orbitals. In this framework, electron delocalisation corresponds to high-probability connections between likely electron arrangements, while resonance arises from the inclusion of additional arrangements that open alternative paths. This approach yields a generalised derivation of the Hückel 4n + 2 rule solely from fermionic antisymmetry and offers a unified, orbital-free description of chemical bonding phenomena.

Valence Bond Theory and Electronic Structure in Chemistry publication trend

The graph below shows the total number of articles in valence bond theory and electronic structure in chemistry across all publications each year (not limited to Nature Index journals).

Technical terms

Valence bond theory: A quantum mechanical model in which chemical bonds arise from the overlap and spin coupling of atomic orbitals, emphasising localized electron pairs and resonance between Lewis structures.

Molecular orbital theory: A framework that describes electrons as delocalised in molecular orbitals formed by the linear combination of atomic orbitals, useful for capturing delocalisation and electronic excitation.

Electron correlation: The interaction between electrons beyond mean-field approximations, crucial for accurately describing energy, structure and bonding in multi-electron systems.

Resonance: The stabilisation resulting from the quantum superposition of two or more electron-pair Lewis structures, reflecting the delocalisation of bonding electrons.

Delocalisation: The spread of electron density over multiple atoms or bonds, as opposed to localisation in a single bond or region, underpinning properties such as conductivity and aromaticity.

Aromaticity: A form of cyclic electron delocalisation characterised by enhanced stability in planar ring systems with (4n + 2) π electrons, as described by Hückel’s rule.

Charge-shift bonding: A bonding paradigm in which the stability arises primarily from resonance between ionic and covalent forms, often driven by Pauli repulsion rather than pure covalent overlap.

π-Backdonation: An interaction in which electron density is donated from a metal d-orbital into an antibonding π* orbital of a ligand, strengthening metal–ligand bonds and affecting reactivity.

References

1. Identifying a real space measure of charge-shift bonding with probability density analysis. Chemical Science (2024).
2. Synergistic Charge Transfer Effect in Ferrous Heme–CO Bonding within Cytochrome P450. Molecules (2024).
3. Valence Bond Theory—Its Birth, Struggles with Molecular Orbital Theory, Its Present State and Future Prospects. Molecules (2021).
4. The electronic structure of benzene from a tiling of the correlated 126-dimensional wavefunction. Nature Communications (2020).
5. Real space electron delocalization, resonance, and aromaticity in chemistry. Nature Communications (2021).
6. On the Nature of the Bonding in Coinage Metal Halides. Molecules (2022).