Preparation, NMR Spectroscopic, and ab Initio/DFT/GIAO-MP2 Studies of Halomethyl Cations1

A series of halomethyl cations was prepared and studied by 13 C NMR spectroscopy. Their structures and 13 C NMR chemical shifts were also calculated by ab initio/DFT/GIAO-MP2 methods. The δ 13 C of trihalomethyl cations CX 3 + (X = Cl, Br, I) and dimethylhalocarbenium ions Me 2 CX + (X = F, Cl, Br) correlate well with the Pauling electronegativities of the halogen atoms and δ 11 B of the isostructural and isoelectronic boron halides as well as with the calculated charge of carbon atoms. The CF 3 + cation was not observed, but a chemical shift of δ 13 C 150 is indicated by comparison with other experimentally observed trihalomethyl cations. GIAO-MP2 chemical shift calculations gave δ 13 C 169.2 for the CF 3 + cation.