Polarisation of Electron Density and Electronic Effects: Revisiting the Carbon–Halogen Bonds

Abstract

Electronic effects (inductive and mesomeric) are of fundamental importance to understand the reactivity and selectivity of a molecule. In this article, polarisation temperature is used as a principal index to describe how electronic effects propagate in halogeno-alkanes and halogeno-alkenes. It is found that as chain length increases, polarisation temperature decreases. As expected, polarisation is much larger for alkenes than for alkanes. Finally, the polarisation mode of the carbon–fluorine bond is found to be quite different and might explain the unusual reactivity of fluoride compounds.

DFT exchange: sharing perspectives on the workhorse of quantum chemistry and materials science

“…Therefore, using the external electrostatic potential as a probe and the polarization energy, entropy, and density as electronic responses, one can get qualitative and quantitative insight into the reactivity and the selectivity of molecular fragments. 483 (3.9.5) Fuentealba : One should not forget that, along with density functionals, one has density functions as a special case. Ramon Carbó-Dorca Carre has studied the mathematical structure of such functions.…”

“…where r k 0 (r) is the transition density coupling the kth state to the ground state. 483 From a link between conceptual DFT and statistical thermodynamics, it has been shown that the perturbation energy due to intermolecular electrostatic interactions can be understood in terms of effective work and heat exchange, 484 the first-order correction Ð r r ð Þdv r ð Þdr being the effective work and the secondorder correction in eqn (60) being the heat exchange. A polarization entropy and a polarization temperature can also been defined by this analogy.…”

“… 482 The stabilization energy due to interaction between the polarization density and the electrostatic potential δ v ( r ) is given by where c k 2 [δ v ( r )] is the oscillator strength of the k th excited state and E 0 − E k is minus the k th excitation energy. 483 Therefore, eqn (60) can be viewed as a minus the energy required to rearrange the electron configuration so that c k 2 electrons are promoted from the ground state to the k th state. Following the same line of thought, the plot of c k 2 versus ( E 0 − E k ) can be considered as a polarization spectrum.…”

“…The polarization density can be computed as where ρ k 0 ( r ) is the transition density coupling the k th state to the ground state. 483 …”

“…Therefore, using the external electrostatic potential as a probe and the polarization energy, entropy, and density as electronic responses, one can get qualitative and quantitative insight into the reactivity and the selectivity of molecular fragments. 483 …”