The DFT B3LYP study on 1-C4H^+~8, 2-C4H^+~8 and C4H^+~10 has been carried out. The molecular structures were optimized at the B3LYP/6- 31G(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/6-311+G(d, p) levels, and the frequency analysis calculations were performed at the B3LYP/6-311G(d, p) level. 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), MP2(full)/6-311G(d, p), and MRSDCI levels. 1-C4H^+~8 is predicted to have a nonplanar structure, which is in contrast to the previous conclusions based on the ab initio and DFT calculations. 2-C4H^+~8 is predicted to have stable cis and trans conformations with planar structures, and C4H^+~10 is predicted to have stable trans and gauche conformations. The calculated hfcc results are in good agreement with experiment and more accurate than the previous theoretical results.

Key words: BUTENE P, BUTANE P, MOLECULAR STRUCTURE, FINE STRUCTURE, QUANTUM CHEMISTRY