Novel silylphenol antioxidants by density functional theory

We have scrutinized five novel silylphenol antioxidants, including 2-silylphenol ( 1 ), 4-silylphenol ( 2 ), 2,6-disilylphenol ( 3 ), 2,4-disilylphenol ( 4 ), and 2,4,6-trisilylphenol ( 5 ), at M06/6–311++G** level of theory. To evaluate the antioxidant efficiency, the electronic effects on O─H bond dissociation energy (BDE) and vertical ionization potential (IP_v) of 1 – 5 are investigated, which are mainly governed by electronic effects. The conductor-like polarized continuum model (CPCM) is applied to measure the antioxidant capacity in the solution phase. The results show that antioxidants with the lowest BDE and IP_v values can efficiently act via hydrogen atom transfer (HAT) and single electron transfer (SET) mechanisms, respectively. The stability of resulting radicals is measured by nucleus independent chemical shift (NICS) index, natural bond orbital (NBO) analysis, and nucleophilicity (N) index. The BDE shows lower values in the gas phase with respect to water, while water exhibits lower IP_v values than gas. Structure 5 turns out as the most efficient antioxidant. The overall order of antioxidant efficiency in both gas and water phases is 5 > 2 > 3 > 4 > 1 .