Exercise 5 Gibbs free energy, which can be used to compute the solvation energy of a molecule: the energy change going from the gas phase to solution. The solvation energy can be computed for the same compound with several solvents in order to understand its relative solubility in different environments. We want to compare the solubility of acetic acid in several solvents: chloroform and water. Optimize the geometry of acetic acid in the gas phase and in both solvents (optimization in solvents can be started from the gas phase-optimized structure) at the M06-2X/def2-TZVP level. Repeat all calculations twice: one using the CPCM solvation model, the other using the SMD solvation model 2. We will compute solvation energy as the difference of the predicted Gibbs free energy values in the gas phase and in solution, taken from the two frequency calculations: Gsolv=GsolventGgas where Gsolv is the Gibbs free energy of solvation. Fill the Table below in order to compare with the experimental value. Which of the two solvents the acetic acid is most soluble? Does this result confirm your general information about the solubility of acetic acid in both solvents? 2 SMD (the Solvation Model based on Density) is a solvation model designed in particular for solvation energies. In some cases (e.g. for very large problems and/or in computing environments where resources are limited) a frequency calculation cannot be performed, we can subtract the solute total energy from the SMD total energy, both computed at the gas phase optimized geometry Gsolv=EsolventEgas Of course, Eq(5.2) is a very crude approximation of Eq (5.1). Exercise 5 Gibbs free energy, which can be used to compute the solvation energy of a molecule: the energy change going from the gas phase to solution. The solvation energy can be computed for the same compound with several solvents in order to understand its relative solubility in different environments. We want to compare the solubility of acetic acid in several solvents: chloroform and water. Optimize the geometry of acetic acid in the gas phase and in both solvents (optimization in solvents can be started from the gas phase-optimized structure) at the M06-2X/def2-TZVP level. Repeat all calculations twice: one using the CPCM solvation model, the other using the SMD solvation model 2. We will compute solvation energy as the difference of the predicted Gibbs free energy values in the gas phase and in solution, taken from the two frequency calculations: Gsolv=GsolventGgas where Gsolv is the Gibbs free energy of solvation. Fill the Table below in order to compare with the experimental value. Which of the two solvents the acetic acid is most soluble? Does this result confirm your general information about the solubility of acetic acid in both solvents? 2 SMD (the Solvation Model based on Density) is a solvation model designed in particular for solvation energies. In some cases (e.g. for very large problems and/or in computing environments where resources are limited) a frequency calculation cannot be performed, we can subtract the solute total energy from the SMD total energy, both computed at the gas phase optimized geometry Gsolv=EsolventEgas Of course, Eq(5.2) is a very crude approximation of Eq (5.1)
