On quantum-chemical estimates of constants of isotropic hyperfine couplingwith protons in free radicals

A scheme of consistent quantum-chemical calculations of constants of isotro pic hyperfine coupling (IHFC) with protons (a(iso)(H)) in free radicals is considered for the case where the spin populations rho(s)(H) are determined In the basic set of symmetrically orthogonalized atomic orbitals taking mo del sigma- and pi-electron fragments as an example. The competence of using two coefficients of proportionality K(H) when estimating the proton IHFC c onstants by semiempirical quantum-chemical methods was demonstrated. Theore tical substantiation of empirical values of the above coefficients previous ly used is revealed.