Aromaticity - Yale...
Transcript of Aromaticity - Yale...
![Page 1: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/1.jpg)
End
Aromaticity
![Page 2: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/2.jpg)
Coal
Coal as a Source of Benzene
1675 - Bituminous coal is distilled to form tars
Coal1000 oCgas + liquid + tar
illuminating gas H2 + CH4
light oil 3.2 gal/ton
60% benzene
tar pitch
asphalt
![Page 3: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/3.jpg)
Faraday
Faraday Isolates Bicarburetted Hydrogen
1825 - Michael Faraday isolates “bicarburetted hydrogen” (C12H6) from liquid residue in a cylinder of illuminating gas. [C = 6, H = 1]
Michael Faraday (1791-1867)
"One Christmas was so much like another, in those years around the sea-town corner now and out of all sound except the distant speaking of the voices I sometimes hear a moment before sleep, that I can never remember whether it snowed for six days and six nights when I was twelve or whether it snowed for twelve days and twelve nights when I was six." "A Child's Christmas in Wales" --- Dylan Thomas
![Page 4: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/4.jpg)
Mitscherlich
The Preparation, Naming and Correct Formula of Benzene
1834 - Mitscherlich prepares benzene (C6H6) from benzoic acid by heating with CaO. Benzoic acid was prepared from gum benzoin resin from Styrax benzoin.
Eilhard Mitscherlich (1794-1863)
![Page 5: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/5.jpg)
Kekule’s Theory
Kekulé’s First Structure of Benzene
1865 - Proposes a cyclic structure for benzene with alternating single and double bonds
August Kekulé
(1829-1896)
1890- Benzene Fest - Kekulé’s Dream
![Page 6: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/6.jpg)
Ladenburg’s Objection
Ladenburg’s Riposte
Ladenburg, a former student of Kekulé’s, objects to his mentor’s formula for benzene because only one o-dibromobenzene is known, not two.
Albert Ladenburg (1842 - 1911)
BrBr
BrBr
![Page 7: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/7.jpg)
Kekule Revised
Kekule’s Response
1872 - Kekulé revises his theory, suggesting that the single bonds are changing places with the double bonds.
BrBr
BrBr
not resonance - barrier implied
![Page 8: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/8.jpg)
Ladenburg’s Prisman
Ladenburg’s Prismane Structure
1869 - Ladenburg proposes the prismane structure for benzene.
.
X
X
X
X
X
X
ortho para meta
![Page 9: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/9.jpg)
Van’t Hoff’s Objection
Van’t Hoff’s Objection
1869 - Ladenburg proposes the prismane structure for benzene.
X
X
X
X
X
X
Van’t Hoff objects to Ladenburg’s prismane structure because the ortho isomer is chiral and should be resolvable.
ortho para meta
![Page 10: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/10.jpg)
Ortho Isomer
The ortho-Isomer
X
X
X
X
X
X
X
X
X
X
![Page 11: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/11.jpg)
Acton and Katz
104 Years Later…
1973 - Acton and Katz synthesize prismane. .
1H NMR: δ 2.28, s 13C NMR: 30.6 ppm
Prismane Benzene
1H NMR: δ 7.34, s 13C NMR: 128.4 ppm
![Page 12: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/12.jpg)
Armstrong-Baeyer (1887)
Other Benzenes
Other Benzenes
Claus (1867)
Dewar (1867) Stadeler (1868) Wichelhaus (1869)
“Dewar benzene”
Thiele (1899)
![Page 13: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/13.jpg)
Cyclohexatriene
Cyclohexatriene vs. Benzene
Std. State
ΔHho = -28.5 kcal/mol
ΔHho = -26.0 kcal/mol
ΔHfo = +25.0 kcal/mol
ΔHfo = +24.0 kcal/mol
ΔHfo = -1.0 kcal/mol
ΔHfo = -29.5 kcal/mol
cyclohexatriene
est. ΔHho = -84.5 kcal/mol
(3 x (-28.5))
est. ΔHfo = +55.0 kcal/mol
ΔHfo = +19.8 kcal/mol
ΔHho = -49.3 kcal/mol
resonance stabilization 35.7 kcal/mol
![Page 14: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/14.jpg)
ΔHho=-49.8 kcal/mol
Is Cyclooctateraene Aromatic?
Is Cyclooctatetraene Aromatic?
ΔHho=-72.4 kcal/mol
Std. State
ΔHho=-24.3 kcal/mol
ΔHho=-98.0 kcal/mol
Δ(ΔHho)=25.6 kcal/mol
Δ(ΔHho)=22.6 kcal/mol
Δ(ΔHho)=25.5 kcal/mol
![Page 15: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/15.jpg)
1H NMR Shifts
7.40 H
H
HH
H
H 5.66 H
H
1H NMR: Aromatic vs. Alkenyl Hydrogens
0 1 2 3 5 7 8 9 6 4 10 δ
Aromatic H Alkenyl H
deshielding / downfield shielding / upfield
![Page 16: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/16.jpg)
Magnetic Anisotropy
Bo Downfield shift for aromatic protons (δ 6.0-8.5)
Magnetic Anisotropy
H H
H H
H H
![Page 17: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/17.jpg)
MOs of Benzene
Molecular Orbitals of Benzene
bonding antibonding
π1 0 nodes
π2 π3 2 nodes
π6* 6 nodes
Aromatic - 4n+2 Frost Diagram
π4* π5
* 4 nodes
![Page 18: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/18.jpg)
MOs of Cyclooctatetraene
Molecular Orbitals of Cyclooctatetraene
Anti-aromatic - 4n
![Page 19: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/19.jpg)
MOs of Cyclooctatetraene Dianion
Molecular Orbitals of Cyclooctatetraene Dianion
Aromatic - 4n+2
![Page 20: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/20.jpg)
MOs of Cyclooctatetraene Dianion
Molecular Orbitals of Cyclobutadiene
Anti-aromatic - 4n
![Page 21: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/21.jpg)
4n + 2 (E,Z,Z,E,Z,Z)-Cyclodecapentaene
4n + 2 (E,Z,Z,E,Z)-Cyclodecapentaene
(E,Z)-Dihedral angle = 48o
(Z,Z)-Dihedral angle = 31o
4n + 2, non-planar; non-aromatic!
![Page 22: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/22.jpg)
1,6-Methano-(E,Z,Z,E,Z,Z)-Cyclodecapentaene
1,6-Methano-(E,Z,Z,E,Z)-Cyclodecapentaene
4n + 2, “planar”; aromatic
(E,Z)-Dihedral angle = 24o
(Z,Z)-Dihedral angle = 0.5o
![Page 23: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/23.jpg)
(E,Z,Z,Z,Z,Z)-Cyclodecapentaene
(E,Z,Z,Z,Z,Z)-Cyclodecapentaene
4n + 2, non-planar; non-aromatic
![Page 24: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/24.jpg)
Naphthalene and Azulene
Naphthalene and Azulene
4n + 2, planar; aromatic
![Page 25: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/25.jpg)
Pyrenes I
14e: aromatic
?
Pyrenes
H3 C
C H3
hν
![Page 26: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/26.jpg)
Pyrenes II
16e: anti-aromatic? 14e: aromatic!
Pyrenes
H3 C
C H3
14e: aromatic
hν
![Page 27: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/27.jpg)
[18]-Annulene
[18]-Annulene
B0 1H NMR:
120OC; δ5.45 (18H,s)
H H
H
H
H
H
HHH
H
H
H
H HH
HHH
-60oC; δ9.25 (12H,s), -2.9 (6H,s)
![Page 28: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/28.jpg)
Aromatic Cations
Aromatic Cations
Cyclopropenium cation
Tropylium cation 1H NMR: δ9.17, singlet
![Page 29: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/29.jpg)
Aromatic Anions
Aromatic Anions
H H
deprotonation
Cyclononatetraenyl anion
H H
pKa = 16
deprotonation
Cyclopentadienyl anion
![Page 30: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/30.jpg)
Aromatic Dianions
Aromatic Dianions I
1H NMR: δ6.75, singlet
Cyclooctatetraene
anti-aromatic
tub-shaped
Cyclooctatetraenyl anion
aromatic
planar
1H NMR: δ5.56, singlet
2 Na=
![Page 31: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/31.jpg)
Aromatic Dianions
Aromatic Dianions II
Dihydropentalene
2 n-butyllithiumH
H
HH
Pentalene dianion
Pentalene
![Page 32: Aromaticity - Yale Universityursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/aromaticity.pdfAromaticity. Coal Coal as a Source of Benzene 1675 - Bituminous coal is distilled to form](https://reader031.fdocuments.net/reader031/viewer/2022021417/5acd17aa7f8b9a27628d3c3d/html5/thumbnails/32.jpg)
End
The End