The paper presents the first application of unrestricted Hartree–Fock formalism to the consideration of spin-orbit coupling (SOC) of open-shell systems in general and sp2 nanocarbons in particular. The SOC parameters determination is exhibited on the example of stretched ethylene. g-Factor determination addresses fullerene C60 due to its peculiar “paradiamagnetic” behavior at low temperature characterized by a set of local spins with different g-factors. The approach application has allowed not only to suggest a reliable explanation of the factor variability but to supplement it by a quantitative agreement with experimental data. © 2017 Taylor & Francis Group, LLC.