Speaker: ke AnAdvisor: Jun Zhu 2012.11.30

A Direct Energetic Measure of Aromaticity Based on a Cleavage of the Rings

in Cyclic Compounds

Abstract

+ 2 +

Homodesmotic reaction1

cyclic acyclicASE

1. Hehre, W. J.; Ditchfield, R.; Radom, L.; Pople, J. A. J. Am. Chem. Soc. 1970, 92, 4796–4801.

Outline

Introduction Results and discussion Conclusion Other work

Introduction

Various criteria: Geometry2

Energy3,4

Magnetism5

Electronic property

2. Krygowski, T. M.; Cyranski, M. K. Chem. Rev. 2001, 101, 1385-1419.3. Slayden, S. W.; Liebman, J. F. Chem. Rev. 2001, 101, 1541-1566.4. Cyranski, M. K. Chem. Rev. 2005, 105, 3773-3811.5. Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.. Schleyer, P. v. R. Chem. Rev. 2005, 105, 3842-3888.

Results and Discussion

Benzene, naphthalene and pyridine were calculated at B3LYP/6-311+G* level, zero-point energy were applied.

6.Cyranski, M. K. Chem. Rev. 2005, 105, 3773–3811.

+ 2ASE = 33.3

+

+ 4ASE = 54.1

2 +

N

+ 2ASE = 29.1

+N

(33.26)

(51.3~54.36)

(31.06)

7.Krygowski, T. M.; Cyranski, M. K. Chem. Rev. 2001, 101, 1385-1419.

Pyrrole, furan and thiophene were calculated at MP2(fc)/6-311+G** level, zero-point energy were applied.

NH

+ 2ASE = 19.0

+NH

O+ 2

ASE = 16.5+

O

S+ 2

ASE = 19.4+

S

(20.67)

(14.87)

(18.67)

+ 4 2 +

+ 4 2 +ASE=46.5

ASE=54.1

Attention: ?

There are two trans π-conjugated configurations in the latter naphthalene.

cis trans-3.6kcal/mol

+ 4 2 +

+ 4 2 +

+ 4 + +

ASE=46.5

ASE=46.1

ASE=46.2

ASEcorr=53.7

ASEcorr=53.3

ASEcorr=53.4

Conclusion:The results above indicate that the cleavage method could be an effective way to evaluate the aromaticity of the cyclic compounds, especially for some cyclic unstrained π-conjugated rings

To examine the scope of the method

Os

PH3

PH3

Cl

Cl+

HOs

PH3

PH3

Cl

Cl+ Os

PH3

PH3

Cl

Cl+

HOs

PH3

PH3

Cl

Cl

ASE=12.3

Os

PH3

PH3

Cl

Cl

+ 2 Os

PH3

PH3

Cl

Cl+

ASE=15.4

Os

PH3

PH3

OC

OC

+H

Os

PH3

PH3

OC

OC+ Os

PH3

PH3

OC

OC

+H

Os

PH3

PH3

OC

OC

ASE=23.5

Os

PH3

PH3

OC

OC

+ 2 Os

PH3

PH3

OC

OC

+ASE=24.5

Os

PH3

PH3

Cl

ClOs

PH3

PH3

OC

OC

When CO replaces chloride ligand, there is a change from nonplanarity to planarity in osmabenzene. The dihedral in the former osmabenzene is 23.9 degrees. So its aromaticity is weaker than the latter one.

Conclusion

We conclude that the new method, based on the energy difference between the cyclic compound and the acyclic one, is able to produce a reliable result to evaluate the ASEs for both organic aromatics and metallaaromatics. In addition, it could be also applied to strained molecules if the strain energy can be evaluated separately.

Other Work

Antiaromatics:

pentalene cyclobutadiene

Nonaromatics:

Os

PH3

PH3

OC

OCosmacyclopentadiene

cyclopentadiene

+ 4 + +

+ 4 + 2

+ 2 2

ASE=-26.0

ASE=-29.6

ASE=-34.3

• This method can also be employed to evaluate the ASEs of antiaromatics.

• The ring strain energy(RSE) of the cyclobutadiene is taken into consideration.

Os

PH3

PH3

OC

OC+ 2 Os

PH3

PH3

OC

OC+

ASE=8.9

+ 2 +ASE= -0.3

However,

it seems to be that the osmacyclopentadiene is aromatic.

How could it happen?

Next Plans

To evaluate the ASEs of other strained molecules.

To extend this method to other organic aromatics and metallaaromatics.

To calculate the energies of the excited states both in aromatics and antiaromatics.