Dimesitylketone O-oxide: verification of an unusually stable carbonyl oxide by NMR chemical shift calculations

NMR chemical shift calculations in combination with geometry optimizations both based on density functional theory were used to identify and to describe dimesitylketone O-oxide (6), which is the first carbonyl oxide that could be generated in solution at − 78°C and investigated by NMR spectroscopy. The conformation of carbonyl oxide 6 is characterized by two orthogonal mesityl rings and a close O,H contact between one of the H atoms of the mesityl methyl groups and the terminal O atom of the carbonyl oxide. The calculated geometry and conformation of 6 are verified by the agreement of calculated and measured NMR chemical shifts. The unusual rearrangement of 6 to an alcohol is explained.