Abstract The structures, vibrational frequencies and interaction energies of acetone and its complexes with various metal cations (Li +, Na +, K + , Rb + Cs +, Mg +, Ca +, Al +, Mg 2+, and Ca 2+) have been determined using the hybrid three-parameter B3LYP density functional method. For all the studied complexes, the carbonyl (C O) stretch vibration is red-shifted by 8–181 cm −1 with respect to the C O vibrational frequency (1731 cm −1) in acetone. Our calculated shifts are in good agreement with available experiments. The chemical origin of the direction and the trend of the C O vibration shift was analyzed by using the nature bond orbital (NBO) theory. Lee’s explanation [J.H. Song, J. Kim, G. Seo, J.Y. Lee, J. Mol. Struct. (Theochem) 686 (2004) 147], based on the electrostatic nature of the interactions, fails in some complexes. Instead, our explanation using electron density redistribution and rehybridization is more efficient and reasonable.