Acceptor numbers (AN) of several halogenated and perfluorohalogenated solvents were determined using P-31 NMR of triethylphosphine oxide (Et3P=O) as a probe. The halogen and/or hydrogen bonding complex, C-X center dot center dot center dot O=PEt3 or C-H center dot center dot center dot O=PEt3, between the probe and solvent molecules was simulated by MP2 and DFT methods. The halogen bonding energies of perfluorohalogenated solvents and iodobenzene with the probe show a good linear correlation to the AN. The results indicate that the AN can act as a possible criterion for the ability of halogen bonding as a specific solvent effect. (C) 2013 Elsevier B.V. All rights reserved.