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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