Ab Initio/DFT/GIAO—CCSD(T) Calculational Study of the t-Butyl Cation: Comparison of Experimental Data with Structures, Energetics, IR Vibrational Frequencies, and ~(13)C NMR Chemical Shifts Indicating Preferred C_S Conformation

摘要

The C_S conformation of the tert-butyl cation 3 was established to be the preferred global energy minimum using a combination of ab initio, DFT, and CCSD(T) methodology with correlation-consistent basis sets. The potential energy surface of methyl rotation involving the conformation C_S and C_(3h) forms, however, in accord with previous studies, is quite flat. The computed IR absorptions of 3 indicate that it has the greatest degree of electron donation from C—H bonds into the C~+—C bonds. The experimental ~(13)C NMR chemical shifts also agree very well with the experimental data.