¹³C NMR Chemical Shifts and Atomic Charges in C₃H₄ ⁺⁺, C₃H₆ ⁺⁺ and C₄H₆ ⁺⁺ Dication Structures: A DFT Study

Structures of C₃H₄ ⁺⁺, C₃H₆ ⁺⁺ and two isomers of C₄H₆ ⁺⁺ dication were investigated by using DFT calculations at B3LYP/6-31G(d) level. Geometry optimization shows that the two structures 1a and 2b were identified as minima on the potential energy surface, whereas 2a and 1b were found to be maxima. ¹³C NMR chemical shifts were calculated by using GIAO-DFT/B3LYP/6-31G(d) method, and were applied to explore the nature of the carbocationic centers in carbodicationic species. Correlations drawn between various atomic charge (Mulliken, NBO, ChelpG, MK and AIM) of carbon atoms and their ¹³C NMR chemical shifts show a linearity only with AIM charges. In addition, NBO analysis provided more informations about charge distribution and chemical bonding in carbodicationic species.