In organic radicals, is there a relationship between the single electron density and electronegativity of the substituent on the atom possessing single electron?
The electronegativity of a substituent is the same as the electronegativity of the whole molecule (due to Sanderson "Electronegativit yequalization principle"). Parr et al related this property to the single-particle density (electron density) suggesting that one can identify the derivative of the energy functinal with respect to the electron density, evaluated at the ground-state density, with the electronegativity (chemical potential) of the system (which in turn can be equivalently defined as the derivative of the ground-state energy with respect to the number of electrons if the system). More insight can be gained in: Parr, Yang "Densit yfunctional theory of atoms and molecules"
thank you Ramón Alain Miranda-Quintana, I understand your first point, (that electronecativity of whole molecule equals the E.N. of the substituent group).
but I don't understand the second idea. what you talk about seems the origin of DFT, but how does it relate to the density of an unpaired electron ? could you be more specific on that ?
I suggest that you read the following publication: https://www.researchgate.net/publication/232248885_A_new_method_to_derive_electronegativity_from_resonant_inelastic_x-ray_scattering
in which the authors derive the electronegativity of a radical from a spectroscopic parameter related to the electronic density of the excited electron.
Best regards
Article A new method to derive electronegativity from resonant inela...