A DFT B3LYP study on the 1-C_6H_(12)~+, 2-C_6H_(12)~+ and 3-C_6H_ (12)~+ radical cations has been carried out. The molecular geometries for various conformations of the three cations were optimized at the B3LYP/6-31G(d,p) B3LYP/6-31+G(d,p), B3LYP/6-311G(d,p) and B3LYP/6- 311+G(d,p) levels, and the frequency analysis calculations were performed at the B3LYP/6-311G(d,p) level. The most stable conformations are predicted for the three cations. Based on the B3LYP/6-311G(d,p) geometries, the proton isotropic hyperfine coupling constants (hfcc's) were calculated at the B3LYP/6-311G(d,p) and MP2 (full)/6-311G(d,p) levels. The calculated hfcc results for 3-C_6H_(12) ~+ are in good agreement with experiment and more accurate than the previous theoretical results. No experimental hfcc data are available for either 1-C_6H_(12)~+ or 2-C_6H_(12)~+. The hfcc's values and the most stable structures for both 1-C_6H_(12)~+ and 2-C_6H_(12)~+ are predicted in the present work.

Key words: HEXENE, DFT B3LYP, FREE RADICAL, CONFIGURATION, FINE STRUCTURE, COUPLING CONSTANTS