UB1LYP method was used to study the geometries together with hyperfine coupling constants (hfccs) and natural atomic occupancies (NAO) for the cyclic (cyclohexanone-type) and bicyclic (camphor-type) iminoxy radicals. The positional and angular dependence of the hyperfine interactions, affected by radical substituents and conformations, was analyzed in terms of different mechanisms of spin density transmission. The calculations predicted a significant distortion of regular conformations and change of hyperfine couplings upon introduction of C=O into cyclohexane iminoxyl and the C=NO spin label into, a boat cyclohexane. Hyperfine splittings of the EPR spectra were compared with the computed hfccs to verify their assignment. (c) 2005 Elsevier B.V. All rights reserved.