Resonanzhybrid

Resonanzhybrid is the real electronic structure of a molecule that cannot be accurately described by a single Lewis structure but by a superposition of several contributing resonance structures. In valence bond theory, these canonical structures differ in how pi electrons and formal charges are arranged; the actual molecule is better represented by a weighted average of them, reflecting delocalized electrons.

In a resonance hybrid, electrons are not confined to a single bond or a single location. This delocalization leads to partial bond character and bond lengths that lie between typical single and double bonds. The concept helps explain why certain molecules are unusually stable and why some properties, such as reactivity and spectroscopy, cannot be accounted for by any one structure alone. The energy stabilization associated with delocalization is often referred to as resonance energy.

Contributions from different resonance structures are not directly measurable; however, chemists judge their importance by criteria such as octet fulfillment, minimal formal charges, and electronegativity considerations. Structures that place charge on appropriate atoms and that obey the octet are usually more significant.

Common examples include benzene, where two Kekulé structures describe alternating double bonds, while the true structure presents equal bond lengths due to delocalization; the carbonate ion, with three equivalent C–O bonds; and the nitrite or nitrate ions, where the negative charge is distributed over several oxygen atoms. In modern chemistry, resonance is often discussed alongside molecular orbitals, but the resonance hybrid remains a foundational concept for understanding delocalization and chemical stability in many systems.