Lasttime1. Geometry optimization2. Vibrational normal mode3. Frequency calculation4. IR and Raman5. Thermochemistry2
Last time 2 1. Geometry optimization 2. Vibrational normal mode 3. Frequency calculation 4. IR and Raman 5. Thermochemistry
Contents1. Explicit solvation models2. Implicit solvation modelsForesmanandFrisch,Chapter5Jensen,Chapter15.63
Contents 3 1. Explicit solvation models 2. Implicit solvation models Foresman and Frisch, Chapter 5 Jensen, Chapter 15.6
Fromvacuumto liquidOur calculations are all in vacuum;- Thermochemistry is based on the gas phase model, i.e., theideal gas model;Vacuum or gas phase properties can be extended to condensedphase?- Geometry, charge, dipole, spectra, bonding, and reactivity?The key change is the solvation free energy;- The net energy change upon transferring the molecule fromthe gas phase into a solvent with which it equilibrates;△Gsol = Gsol -Ggas4
From vacuum to liquid • Our calculations are all in vacuum; – Thermochemistry is based on the gas phase model, i.e., the ideal gas model; • Vacuum or gas phase properties can be extended to condensedphase? – Geometry, charge, dipole, spectra, bonding, and reactivity? • The key change is the solvation free energy; – The net energy change upon transferring the molecule from the gas phase into a solvent with which it equilibrates; 4 ΔGsol = Gsol – Ggas
Freeenergysurfacefromgasto liquidgas-phaseThick lines on the two surfacessurfaceindicate some chemicalreaction proceeding fromoneAGg(x,y)minimum-energy structuretoanother;EsolvatedNote that there is nosurfacerequirement forthe x and ycoordinates of equivalentstationary points on the two[ (x,y)surfaces to be the same;△Gsol = Gsol - GgasPolarsolvents shift theequilibrium to right;5
Free energy surface from gas to liquid • Thick lines on the two surfaces indicate some chemical reaction proceeding from one minimum-energy structure to another; • Note that there is no requirement for the x and y coordinates of equivalent stationary points on the two surfaces to be the same; 5 ΔGsol = Gsol – Ggas • Polar solvents shift the equilibrium to right;
Born-HabercycleforcomputationofafreeenergychangeinsolutionAG (gas)BW(gas) +A(gasX(gas) +(gas)AGS(W)AG%(A)△G%(B)AG(X)e.g.Menschutkin△G%(...)AG%(.)reaction has differentB(sol)W(sol)energy profiles in gasA(sol)X(sol)+4AG(snhandinwaterAGgasGs(+)HoNgasTAGgasphaseaqueousAGs(R)AGs(FsolutionGStHaNCH + CINHa + CHgCIAGSolR*QReaction coordinate6Arbitrary coordinate
Born–Haber cycle for computation of a freeenergy change in solution 6 e.g. Menschutkin reaction has different energy profiles in gas and in water