Handbook of Solvents - George Wypych - ChemTech - Ventech!

750 Roland Schmid
tween calculated and experimental solvation energies for selected inert gases and nonpolar
large solutes. 54
In the paper referred to, 54 the relevance of the theoretical considerations has been
tested on experimental solvation free energies of nitromethane as the solute in select solvents.
The total solvation energy is a competition of the positive cavity formation energy
and the negative solvation energy of dispersion and dipolar forces,
ΔG = ΔG + ΔG + ΔG
[13.1.11]
cav disp dipolar
where the dipolar term includes permanent and induced dipole interactions. The
nitromethane molecule is represented by the parameters of the HS diameter σ = 4.36 Å, the
gas-phase dipole moment μ = 3.57 D, the polarizability α = 4.95 Å , and the LJ energy
ε LJ/k=391K. Further, the solvent is modeled by spherical hard molecules of spherical
polarizability, centered dipole moment, and central dispersion potential. To calculate the
dipolar response, the Padé approximation was applied for the chemical potential of solvation
in the dipolar liquid and then extended to a polarizable fluid according to the procedure
of Wertheim. The basic idea of the Wertheim theory is to replace the polarizable liquid of
coupled induced dipoles with a fictitious fluid with an effective dipole moment calculated in
a self-consistent manner. Further, the Padé form is a simple analytical way to describe the
dependence of the dipolar response on solvent polarity, solvent density, and solute/solvent
size ratio. The theory/experiment agreement of the net solvation free energy is acceptable as
seen in Table 13.1.3 where solvent ordering is according to the dielectric constant. Note that
the contribution of dispersion forces is considerable even in strongly polar solvents.
Table 13.1.3. Thermodynamic potentials (kJ/mol) of dissolution of nitromethane at
25°C. Data are from reference 54
Solvent εs ΔGcav ΔGdisp ΔGdipolar ΔG(calc) ΔG(exp)
n-C6 1.9 23.0 -32.9 -2.2 -12.1 -12.1
c-C6 2.0 28.1 -38.1 -2.8 -12.7 -12.0
Et3N 2.4 24.2 -33.5 -2.9 -12.2 -15.2
Et2O 4.2 22.6 -33.4 -5.8 -16.5 -17.5
EtOAc 6.0 28.0 -38.5 -9.7 -20.1 -21.2
THF 7.5 32.5 -41.5 -12.2 -21.1 -21.3
c-hexanone 15.5 35.1 -39.8 -17.9 -22.6 -21.8
2-butanone 17.9 28.3 -33.9 -18.9 -24.5 -21.9
Acetone 20.7 27.8 -31.2 -22.1 -25.5 -22.5
DMF 36.7 38.1 -32.1 -28.5 -22.5 -23.7
DMSO 46.7 41.9 -31.1 -31.0 -20.2 -23.6
With an adequate treating of simple forms of intermolecular attractions becoming
available, there is currently great interest to making a connection between the empirical
scales and solvation theory. Of course, the large, and reliable, experimental databases on