The solvent effect of CCl4 on the C=O stretching mode of acetone is studied by carrying out ab initio MO calculations for an acetone-(CCl4), cluster. It is shown that the electric field operating on the C=O bond of acetone is significantly larger than that expected for the reaction field induced by the dipole moment of acetone, and is in the direction that the chlorine atoms look as if they had large positive charges. It is suggested that the atomic quadrupoles of the chlorine atoms, generated by the covalent bonds with the carbon atom, give rise to this effect. (C) 2002 Elsevier Science B.V. All rights reserved.