Density functional study of some aliphatic semidione radical ions

B3LYP density functional with 6-31G * basis set has been used to estimate ESR proton hyperfine coupling constants for a series of rigid semidione radical ions. The calculated estimates are in excellent agreement with experimental results. Single- point UB3LYP calculations have also been made using tJHF/3-21G and UAM2 optimized geometries. Interestingly, the results of these computationally cheaper calculations are also in good agreement with the experimental results.