Ab initio study of molecular structure and hyperfine coupling constants of 1,3,5-cycloheptatriene radical cation

Geometrical optimizations for the radical cation of 1,3,5-cycloheptatriene (CHT+) were performed at different levels of theory, UHF, UMP2, CASSCF and DFT/B3LYP, with the 6–31G(d) basis set. In all cases, planar structures with the C2ν symmetry were obtained. Vibrational analyses showed that the C2ν planar structure is at a local minimum and not very rigid for the ring inversion. Using the optimized structure, the hyperfine coupling constants for hydrogen atoms in CHT+ were calculated and were compared with the experimental values. The UHF and UMP2 calculations failed to predict the hyperfine coupling constants (hfcc) correctly, while DFT hfcc agreed well with experiments.