Zeinab Mokhtari 1

15-December-2009

Two important fundamental molecular properties : - The ionization potential (

IP

) - The electron affinity (

EA

)

The ionization potential (IP) is the energy required to remove an electron from a molecule.

R → R + + e  H = IP The electron affinity (EA) is the energy difference between the anion and the neutral.

R + e → R  H = -EA It has a small value. So difficult to be measured.

2

E Vacuum level =0 eV EA

LUMO

IP

HOMO

3

Oxidation and Reduction

reduction oxidation e EA

LUMO Vacuum level

e LUMO IP HOMO

HOMO

E red E ox

4

The major purpose : To obtain EA of aromatic hydrocarbons reduction potentials in aprotic solvents from half wave - Fullerenes - Organic molecules containing O, N, and halogen atoms - Nucleic acids and other biologically significant molecules A second objective: To calculate the electronegativities,

(EN)=(IP+EA)/2

, of the aromatic hydrocarbons by using ionization potentials in the literature.

5

ECD or NIMS EA evaluation methods Gas phase measurment EA= 2EN-IP EA = -E

1/2

Semiempirical methods PES TCT

6

THE METHOD OF CALCULATING EA’S FROM HALF WAVE REDUCTION POTENTIALS

The first experimental method for obtaining relative electron affinities.

 G is the solution energy difference for the reaction in the gas phase and in solution.

mddG(  G) is a function of charge density.

7

Before the 1960’s: it was assumed that the mddG were the same for different molecules.

By gas phase electron affinities measurement, the mddG values range from 1.7 eV for the large fullerenes to 2.7

eV for small anions.

They make some different groups with different mddG: 8

E 1/2

Bergman Dewar set CURES EC MINDO/3 Semiempirical methods 9

Gas phase EA Some Calculative Methods 10

11

12

Different intercepts for different groups Slope = 1 13

σ(EA) = EA(Experimental) – EA(calculated) 14

σ(EA) = EA(Experimental) – EA(calculated) More precise results 15

Constant ‘‘Is the electronegativity constant?’’ Slope = 1 16

A series of aromatic hydrocarbons

Electronegativity EN is almost constant vs. size and close to the workfunction of graphite (4.3 eV).

17

18