Welcome
Professor Lin
to direct our group!
Self-introduction
Name: Yulei.Hao
Hometown: Shou County in Anhui Province
Mother school: Hefei University of Technology
合肥工业大学
Grade: First-year graduate
2
σ-Aromaticity Review and σ-Aromaticity
investigation of 3MRs transition metal
alkylidene complexes
Reportor: Yulei Hao
Advisor: Jun Zhu
1
Introduction of σ-Aromaticity
2
Computed methods
3
Results and Discussion
4
Further work
4
1
Introduction of σ-Aromaticity
Dewar firstly proposed the concept of σ-
cyclopropane
Aromaticity to explain the anomalous behavior of
cyclopropane such as the upfield 1HNMR chemical
shift (1.25ppm to 0.22ppm), small difference of
CSE (conventional strain energy) compared with
cyclobutane , 27.5 kcal mol-1 and 26.5 kcal mol-1
respectively. He concluded that σ-Aromaticity
energy compensate the high strain energy, and σring induce the diamagnetic property.
σ-Conjugation and σ-Aromaticity
Figure1. Magnetic lines of force in cyclopropane.
M. J. Dewar, Bull. Soc. Chim. Belg. 1979, 88, 957-967
5
1
Introduction of σ-Aromaticity
The two structure models of cyclopropane
Walsh
three trignal near-sp2 methylene carbenes
Coulson and Moffitt
three bent C(sp3)-C(sp3)bonds
6
1
Introduction of σ-Aromaticity
Table1. the deveiopment of cyclopropane of σ-Aromaticity and evaluation criteria.
author
concept
Method or
conclusion
1979 Dewar
σ-Aromaticity
proposed σ-ring current and aromaticity
energy
1985 Cremer
electron density and surface
delocalization
ab initio caculation
1996 Schleyer
NICS values
absolute magnetic shieldings coputed at ring
centers
2001 Schleyer
intrinsic bond
energy
evaluate ASE (11.3 kal.mol-1)
2002 Schleyer
ISE
simple way to evaluation ASE
2005 Schleyer
2007 Folwer
2009
Wu Wei and
Schleyer
evaluation ASE and correlated well with
ECRE(extra cyclic resonance energy)
NICS
coupled Hatree-Fock
σ-ring current
"ipsocentric"
VBSCF motheod,
small σ-ASE (3.5 kal mol-1)
ECRE
7
1
Introduction of σ-Aromaticity
References:
Theoretical Determination of Molecular Structure and Conformation. 1 5.
Three-Membered Rings: Bent Bonds, Ring Strain, and Surface Delocalization
J. Am. Chem. Soc. 1985, 107, 13, 3805.
Nucleus-Independent Chemical Shifts: A Simple
and Efficient Aromaticity Probe
J. Am. Chem. Soc. 1996, 118, 6317.
Theoretical Bond Energies: A Critical Evaluation
J. Phys. Chem. A 2001, 105, 3407-3416.
Recommendations for the Evaluation of Aromatic Stabilization Energies
Org. Lett. 2002, 4, 2873-2876.
An Energetic Measure of Aromaticity andAntiaromaticity Basedon the
Pauling–Wheland Resonance.
Chem. Eur. J. 2006, 12, 2009-2020.
The ring current in cyclopropane
Theor. Chem. Acc. 2007, 118, 123-127.
Is Cyclopropane Really the s-Aromatic Paradigm?
Chem. Eur. J. 2009, 15 9730-9736.
8
1
Introduction of σ-Aromaticity
ISE: isomeric stabilization energy
The differences between a methyl derivative of the aromatic
system and its nonaromatic exocyclic methylene isomer.
Recommendations for the Evaluation of Aromatic Stabilization Energies
Org Lett.Vol. 2002, 4, 2873-2876
.
9
1
Introduction of σ-Aromaticity
ECRE: extra cyclic resonance energy
The RE (resonance energy) difference between a fully
cyclic aromatic compound and appropriate acyclic model.
An Energetic Measure of Aromaticity and Antiaromaticity Based
on the Pauling–Wheland Resonance.
Chem. Eur. J. 2006, 12, 2009-2020.10
1
Introduction of σ-Aromaticity
a
b
Fig. 3 a Current density map for cyclopropane. b the sum of localised C–H bonds of the
cyclopropane molecule. The current induced in the plane of the carbon nuclei by a
perpendicular external magnetic field is calculated at the (CTOCD-DZ/ 6-31G**//RHF/6-31G**)
level.
The ring current in cyclopropane.
Patrick W. Fowler Theor. Chem. Acc. 2007, 118, 123-127.
11
2
Computed Methods
Opt
DFT: B3LYP
Base sets: 6-31G* and LanL2DZ
NICS
DFT: B3LYP
Base sets: 6-311++G** and LanL2DZ
ASE
DFT: B3LYP
Base sets: 6-31G* and LanL2DZ
12
3
Results and Discussion
13
3
Results and Discussion
14
3
Results and Discussion
Table 2. NICS values [ppm] of non-metal rings1-3 and alkylidene
compelexes rings 4-18.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
NICS(0)
NICS(0)ZZ
NICS(1) a
NICS(1)ZZ b
-8.1
-28.3
-42.4
-33.8
-20.2
-39.5
-31.6
-25.2
-35.7
-13.2
-36.6
-36.0
-33.5
-47.5
-33.2
-45.5
-39.0
-31.7
-14.5
-18.2
-29.8
-59.1
-41.7
-65.6
-54.6
-21.2
-51.5
-25.5
-60.5
-63.0
-55.3
-65.4
-42.4
-69.6
-49.0
-41.2
-10.2
-6.9
-8.6
-18.8
-13.5
-18.9
-24.1
-17.6
-16.5
-9.6
-20.2
-18.4
-17.1
-19.2
-16.3
-18.5
-19.1
-17.0
-29.1
-15.1
-24.2
-21.4
-16.9
-24.9
-35.9
-20.2
-22.4
-11.5
-29.6
-28.1
-25.8
-30.0
-24.4
-25.7
-25.8
-24.4
a, b These are the average values of above and below center(0) 1Å.
15
3
Results and Discussion
Benzene
Fig. 4 Comparison of NICS(0) with NICS(1), and NICS(0)ZZ
with NICS(1)ZZ based on the result in table 2.
16
3
Results and Discussion
17
4
Further work
• Try to find other ways to evaluate σ-Aromaticity
energy by VB.
• Explain the NICS results reasonably.
18
Thank you !
19