Quantitative decomposition of resonance‐assisted hydrogen bond energy in β‐diketones into resonance and hydrogen bonding (π‐ and σ‐) components using molecular tailoring and function‐based approaches

Using the molecular tailoring and function‐based approaches allows one to divide the energy of the O─H⋯O═C resonance‐assisted hydrogen bond in a series of the β‐diketones into resonance and hydrogen bonding components. The magnitude of the resonance component is assessed as about 6 kcal mol−1. This value increases by ca. 1 kcal mol−1 on going from the weak to strong resonance‐assisted hydrogen bonding. The magnitude of the hydrogen bonding component varies in the wide range from 2 to 20 kcal mol−1 depending on the structure of the β‐diketone in question. Energy of the intramolecular O─H⋯O═C resonance‐assisted H‐bond in the β‐diketones is estimated via molecular tailoring approach (MTA) and function‐based approach (FBA). Former approach yields estimate of “pure” H‐bond (σ‐component) while latter approach yields the total energy of resonance‐assisted H‐bond. Difference in energy estimated by FBA and MTAs provides a quantitative assessment of the resonance effect in the resonance‐assisted H‐bond (or π‐component).