Abstract
We present the linear response function of bond-orders (LRF-BO) based on a real space integration scheme for molecular systems. As in the case of the LRF of density, the LRF-BO is defined as the response of the bond order of the molecule for the virtual perturbation. Our calculations show that the LRF-BO enables us not only to detect inductive and resonating effects of conjugating systems, but also to predict pKa values on substitution groups via linear relationships between the Hammett constants and the LRF-BO values for meta- and para-substituted benzoic acids. More importantly, the LRF-BO values for the O-H bonds strongly depend on the sites to which the virtual perturbation is applied, implying that the LRF-BO values include essential information about reaction mechanism of the acid-dissociation of substituted benzoic acids.
Highlights
During the past decades, the main branch of contemporary computational chemistry has been developed mainly to simulate chemical phenomena realistically, typically with quantum mechanics/molecular mechanics (QM/MM) methods [1,2]
We presented the linear response function of bond-order (LRF-BO) based on a real space integration scheme
We presented the fundamental features of the linear response function of bond-orders (LRF-BO) values for non-polar and polar covalent bonding systems
Summary
The main branch of contemporary computational chemistry has been developed mainly to simulate chemical phenomena realistically, typically with quantum mechanics/molecular mechanics (QM/MM) methods [1,2]. The LRF is reported to have maximum values at transition states for several Diels-Alder reactions, being another important descriptor of chemical reactions [13] These two properties, together with other properties, such as softness and hardness that have been well-known concepts in general chemistry, are defined as energy derivatives or grandcanonical potential (at T = 0 K) derivatives with v, N, and chemical potential, μ, and are related to each other [3,5,14], enabling us to understand intrinsic properties of molecules in a quantitative way using ab initio computational results. We inspect dependency of δBOH/δv(K) values on K, i.e., the site to which we apply the perturbation, and discuss the implication of the LRF-BO values in describing chemical reaction mechanism of the acid dissociations
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