This work presents the computation of spin-spin coupling that arise between interactions of spin-centers which eventually leads to zero-field splitting in organic molecules. With DFT implementation spin-spin Hamiltonian is subjected to recently observed compact trimethylenemethane analogue di-radicals -nitroxide-substituted nitronyl nitroxide and iminonitroxide, which exhibits large positive exchange interactions with ZFS at the room temperature. We obtain the parameters defining the ZFS that have an excellent agreement with the experiment, consistent with the perception that spin-orbit coupling contribution to the ZFS is negligible in organic molecule. g-tensor shift also calculated with restricted DFT-linear response formalism (RDFT-LR) and compared with realistic observations. (C) 2010 Elsevier B.V. All rights reserved.