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

A Direct Energetic Measure of Aromaticity Based on a

Cleavage of the Rings in Cyclic Compounds

Speaker: Ke AnAdvisor: Jun Zhu

2013/11/08 1

Conclusion

Results and Discussion

Motivation

Introduction

Main ContentMain Content

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IntroductionIntroduction

1. Criteria of Aromaticity

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Structural Criteria

Magnetic Criteria

Planarity Equal bond length tendency Krygowski et al, Chem. Rev. 2001, 101, 1385.

Diamagnetic susceptibility exaltation (Λ) Pascal, P. Ann. Chim. Phys. 1910, 19, 5 Pink, Trans. Faraday Soc. 1948, 4, 407 Schleyer, Pure Appl. Chem. 1996, 68, 209

H+ NMR Chemical Shift Paquette et al, J. Am. Chem. Soc. 1990, 112, 8776 Sekiguchi et al, J. Am. Chem. Soc. 1991, 113, 7081

NICS (Nucleas-Independent Chemical Shifts) Schleyer et al, J. Am. Chem. Soc. 1996, 118, 6317

IntroductionIntroduction

1. Criteria of Aromaticity

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Reactive Criteria

Energetic Criteria

Electrophilic aromatic substitution

HOMA= 1-257.7/n∑(dopt-di)2

Krygowski et al, Tetra. Lett. 1972, 13, 3839.

RE (resonance energy) Schaad et al, Chem. Rev. 2001, 101, 1465.

ASE (aromatic stabilization energy) Cryanski et al, Tetrahedron 2003, 59, 1657.

ISE (isomerization stabilization energy) Schleyer et al, Org. Lett. 2002, 4, 2873. Wannere et al, Org. Lett. 2003, 5, 2983. J. Zhu et al, Org. Lett. 2013, 15, 2442.

IntroductionIntroduction

2. Isomerization Stabilization Energy

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CH3CH2H

H ISE(S0) = -33.2

C1 Cs

Schleyer et al, Org. Lett. 2002, 4, 2873.

H

H

H

H

ISE(S0) = -29.0

Wannere et al, Org. Lett. 2003, 5, 2983.

IntroductionIntroduction

3. Baird’s Rule

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Rules for ground state aromaticity are reversed in the lowest triplet state.

4n rings: “aromatic character”

4n+2 systems: “antiaromaticity”.

S0 T1

aromatic antiaromatic

antiaromatic aromatic

D6h

D8h

Baird, N.C. J. Am. Chem. Soc. 1972, 94, 4941

Motivation

To develop an energetic method to evaluate the triplet aromaticity.

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CH3CH2H

H ISE(S0) = -33.2

C1 Cs

nonaromatic aromatic

Results and Discussion

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CH2H

H

CH3

(1)

H

CH2H

HH

CH3

ISE = 3.4 (2)

HHHH

H

1b1a

ISE = 13.5

ISEcorr. = 16.9

Results and Discussion

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Structures and energies of anti- and syn-butadiene conformations in their S0 and T1 states.

Results and Discussion

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CH2H

H

CH3

ISE = -12.0(3)

2b2a

2+ 2+ISEcorr. = -14.5

CH2

H

HCH3

ISE = -15.6

ISEcorr. = -24.7

CH2

H

H

CH3

ISE = -24.2

ISEcorr. = -24.6

4b4a

3b3a

(5)

(4)

Results and Discussion

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ISE = 0.6ISE = -22.5

ISE = -13.7HSi

ISE = -16.1HB

ISE = -16.4

CH2CH2

CH2

CH2

CH2

HH

H

H

H

HH

H

H

H

(11)

10b10a

ISE = -12.5

H3CH2C

H

H

5aCH3

HSi

CH3

HB

CH3

CH3

CH3

(6)

(7)

(8)

(9)

(10)

5b

6b

7b

8b

9b9a

8a

6a

7a

Results and Discussion

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HSi

9

2+1

2

3

4

7

6

5

HB

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Plot of ISE vs NICS(T1;1)zz for a series of planar monocyclic species with 4n and 4n+2 electrons in the T1 state.

Conclusion

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The ISE method can be extended to confirm the aromaticity of the T1 state of 4n -cyclic species.

Most annulenes with 4n+2 -electrons in the T1 state have a strong tendency to reduce their antiaromaticity by nonplanar deformations.

Thanks For Your Attention !

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