Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.
-
Upload
patricia-mills -
Category
Documents
-
view
239 -
download
9
Transcript of Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.
![Page 1: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/1.jpg)
Ch. 14 - 1
Chapter 14Chapter 14
Aromatic CompoundsAromatic Compounds
Modified from sides of William Tam & Phillis Chang
![Page 2: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/2.jpg)
Nomenclature
Naming monosubstituted benzenesMost: benzene is the parent name and the substituent is a prefix
benzene
![Page 3: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/3.jpg)
Other simple, common benzenes, have accepted parent name (for substituent and ring)
![Page 4: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/4.jpg)
Disubstituted benzenesWith two substituents:
Their relative positions are indicated by prefixesor numbers : ortho- (abbreviated o-, or 1,2-) meta-, (m- , 1,3-) para-, (p- , 1,4-)
![Page 5: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/5.jpg)
examples
![Page 6: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/6.jpg)
Dimethylbenzenes = xylenes
![Page 7: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/7.jpg)
More than two groups1. Positions must be indicated by numbers
2. Number the benzene ring to giveSubstituents the lowest possible numbers
![Page 8: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/8.jpg)
More than two different substituents list in alphabetical order
![Page 9: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/9.jpg)
A substituent gives “special” base name (aniline, anisole, etc.) that substituent is position 1
![Page 10: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/10.jpg)
Benzene as a substituent = phenyl group (C6H5)
hydrocarbon with saturated chain and 1 benzene ring Base/parent is the larger structural unit.
butylbenzene t-butylbenzene (S)-2-phenylheptane
![Page 11: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/11.jpg)
Unsaturated chains, the parent/base name is of that chain, (regardless of ring size)
trans-1-phenyl-2-butene
![Page 12: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/12.jpg)
Benzyl (Bn) is a common name for the phenylmethyl group
![Page 13: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/13.jpg)
recall
![Page 14: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/14.jpg)
![Page 15: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/15.jpg)
substitution not additionReactions of Benzene
[+ HBr] substitution
![Page 16: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/16.jpg)
The Kekulé Structure for Benzene
![Page 17: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/17.jpg)
These 1,2-dibromobenzenes are not isomers
RESONANCE
or an equilibrium
X
X
![Page 18: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/18.jpg)
+ other Br2 additons
However
aromatic character?
![Page 19: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/19.jpg)
3-D structure
π-electrons above and below ring
Note: Planar structure All carbons sp2 hybridized
![Page 20: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/20.jpg)
Hückel’s Rule: The 4n + 2 π Electron Rule
(1) Planar monocyclic rings (2) containing 4n + 2 π electrons, where n = 0
or an integer (2, 6, 10, 14 . . .etc.) have substantial resonance energies, “aromatic”
i.e. a planar ring containing 6 π electrons is “aromatic”
![Page 21: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/21.jpg)
Hückel’s rule states that planar monocyclic rings with 2, 6, 10, 14 . . . delocalized electrons should be aromatic
![Page 22: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/22.jpg)
How To Diagram the Relative Energies of p How To Diagram the Relative Energies of p Molecular Orbitals in Monocyclics Molecular Orbitals in Monocyclics Based on HückelBased on Hückel’’s Rules Rule
circledpolygon
antibonding orbitals
nonbonding orbitals
bonding orbitals
type of orbitals
orbitalenergy levels
![Page 23: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/23.jpg)
π molecular orbitals of cyclooctatetraene, if planar Predicted to have 2 nonbonding orbitals and
an unpaired electron in each nonbonding orbital
Not be expected to be aromatic
![Page 24: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/24.jpg)
System not planar
The bonds alternately long and short; (1.48 and 1.34 Å)
![Page 25: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/25.jpg)
The AnnulenesThe Annulenes
Hückel’s rule predicts that annulenes will be aromatic
if the molecule has 4n + 2 π electrons and have a planar carbon skeleton
![Page 26: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/26.jpg)
All these (4n + 2)π, planar annulenes are aromatic
![Page 27: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/27.jpg)
Non-planar (4n + 2)π annulenes are antiaromatic
![Page 28: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/28.jpg)
(4n) non-planar annulenes are antiaromatic
![Page 29: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/29.jpg)
NMR Spectroscopy: Evidence for ElectronNMR Spectroscopy: Evidence for Electron Delocalization in Aromatic CompoundsDelocalization in Aromatic Compounds
1H NMR spectrum 1H occurs at relatively high frequencyIs compelling evidence for aromaticity
![Page 30: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/30.jpg)
(δ -3.0)
(δ 9.3)
![Page 31: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/31.jpg)
Aromatic Ions
pka = 16 pka = 36
pKa unsaturated and saturated hydrocarbon 44-53
![Page 32: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/32.jpg)
sp3 sp2
6 π electrons aromatic
![Page 33: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/33.jpg)
strong base
LA
![Page 34: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/34.jpg)
Aromatic, Antiaromatic, and Nonaromatic Aromatic, Antiaromatic, and Nonaromatic CompoundsCompounds
An aromatic compound has its π electrons delocalized over the entire ring and
It is stabilized by the π-electron delocalization
Evaluation: compare cyclic compound vs acyclic with same number of electrons.
![Page 35: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/35.jpg)
Ring is aromatic if the ring has lower -electron energy then the acyclic chain
Based on sound calculations or experiments
Nonaromatic if the ring and the chain have the same -electron energy [non-planar]
Antiaromatic if the ring has greater π-electron energy than the open chain [4n e’s]
![Page 36: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/36.jpg)
Cyclobutadiene
Benzene
![Page 37: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/37.jpg)
Other Aromatic Compounds
Benzenoid polycyclic aromatic hydrocarbons having two or more fused benzene rings.
Benzenoid Aromatic CompoundsBenzenoid Aromatic Compounds
![Page 38: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/38.jpg)
Nonbenzenoid Aromatic CompoundsNonbenzenoid Aromatic Compounds
![Page 39: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/39.jpg)
FullerenesFullerenes
![Page 40: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/40.jpg)
Heterocyclic Aromatic Compoundsheterocyclic compounds cyclic compounds with an
element(s) other than carbon, e.g. piperidine
aromatic heterocyclic:
![Page 41: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/41.jpg)
Examples of useful heterocyclic aromatic compounds
![Page 42: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/42.jpg)
Aromaticity
![Page 43: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/43.jpg)
Basicity of nitrogen-containing heterocycles
![Page 44: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/44.jpg)
Basicity of nitrogen-containing heterocycles
poor base:
loss of aromaticity
still aromaticityimidazolearomatic weak base
![Page 45: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/45.jpg)
Aromatic Compounds in Biochemistry
Two amino acids necessary for protein synthesis contain the benzene ring
![Page 46: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/46.jpg)
Derivatives of purine and pyrimidine are essential parts of DNA and RNA
![Page 47: Ch. 14 - 1 Chapter 14 Aromatic Compounds Modified from sides of William Tam & Phillis Chang.](https://reader034.fdocuments.in/reader034/viewer/2022042508/56649d835503460f94a6a1f8/html5/thumbnails/47.jpg)
Nicotinamide adenine dinucleotide important coenzymes in oxidations and reductions
-pyridine derivative (nicotinamide) -purine derivative (adenine)
O O