TIP= relat.ivo salvation of the ground and the excited states corresponding to the n -L R* W transition of carbonyl chromophores is determined, for a serie of solvents, on the basis of (11 the value of AE = hv, (2) the salvation enthaipy of the ground state determined by calorimetry, (3) the enthaipy of cavity formation. The importance of the Iast contr~ution is emphasized. The n + IT* transition energy of an unconjugated carbonyl group is solvent sensitive and characterized by the so-called blue-shift in solvents of increased polarity. This blue-shift has been explained by a better stabilization of the ground state of the molecule compared to its excited state. This simple interpretation is based on arguments involving the iower value of the dipole moment of the excited state with respect to the ground state [2] _ Recently, Haberfield [3] claimed that, by calorimetry, he was able to estimate the relative solvation of the ground state of acetone and benzophenone in various solvents. The method used by Haberfield was described previously by Arnett et at. [4] and applied by these authors to other systems. This method is based on the assumption that the heat of transfer of a solute from solvent to solvent is a direct measure of the relative position of the solute ground state in each solvent. Therefore, according to these authors, the measurement of the A.5 = hv values of a particular electronic transition of the solute in the same series of solvents gives directly the relative positions of tie excited state in alI the solvents f3,4]. From such a study, ~aber~eld concluded that the * ForpartIoftKsseriesseeref. [I].