Implicit Solvent Effects

Question 1

Why are properties effected more by solution?

Answer 1

Neighbouring molecules effect molecular properties, in gas-phase (more disperse) the effects are negligible but in solution they are much more present

Question 2

Implicit solvent modelling

Answer 2

Computation that treats solvent as an electric field

Question 3

How does solvation effect polar molecules

Answer 3

Increases their polar dipole moment
Stretching their bond lengths
Lowers G

(roughly proportional to polarity of solvent and solute)

Question 4

What does lowering G effect?

Answer 4

Effects delta G rxn and delta G ts
(reaction and activation energies)

Question 5

What will happen to energies if the delta rxn | u = dipole moment | > 0

Answer 5

Solvation will lower delta G rxn

(same relation ship for delta rxn | u = dipole moment |ts and delta G ts)

Question 6

Can transition states disappear upon solvation?

Answer 6

Yes

Question 7

What is Gch in Gp?

Answer 7

The work required to create the separation of charge

Three forms for computing Gch, so three forms for computing Gp

Question 8

What are the three methods for computing Gch?

Answer 8

Poisson method
Generalized Born approach
Conductor-like screening model

Question 9

Poisson method

Answer 9

External potential of solvent reaction field (o(r)) depends on disturbance (p(r)) and the solvent’s dialectric constant (ability to respond to disturbance)

Question 10

Spherical molecule in Poisson

Answer 10

Integral is easy, result is Born equation:
Gp = -0.5( 1-1/e ) ( q^2 / a )

Gaussian uses overlapping sphere cavities and numerical integration

Question 11

Generalized Born approach

Answer 11

Steps bypassed and Gp equation altered (no Gch) by trating molecule as a set of monatomic atoms with partial charge qk

Question 12

Conductor-like Screening Model (COSMO, CPCM)

Answer 12

Simplified Poisson method
(1) pretend dielectric constant is infinity
(2) back correct for true dielectric constant value