We reproduce the general trend that the frequency of the carbonyl stretching mode is redshifted and broadened the more polar the solvent. The frequency of the carbonyl stretching mode drops from 1815 cm -1 in cyclohexane (non-polar), to 1797 cm -1 in acetonitrile (intermediate polarity), and to 1769 cm -1 in water (high polarity). Comparing the solvent shifts, the shift from cyclohexane to acetonitrile is 18 cm -1 , while the experiment reports a shift of 9 cm -1 . We thus overestimate the solvent shift by a factor of two. The same applies to the shift when going from acetonitrile to water, which is 28 cm -1 in our work and 14 cm -1 experimentally. Using a vibrational scaling factor would reduce these discrepancies. However, the appropriate scaling factor in this case would have a minor impact on the solvent shifts. Our calculated solvent shifts are twice as large as the experimental ones. This result is higher than the maximum basis-set error found in the benchmark calculations (see Sec. 4). This can possibly be explained by the errors introduced by the partitioning of our system into a core and environment region. In particular, the hydrogen bonds, which are especially important for the carbonyl stretching mode, cross the two parts and are only partially accounted for by the PE-QM approach.