1 not necessarily stinky aromatic compounds. historical significance spices and herbs desire to...
TRANSCRIPT
![Page 1: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/1.jpg)
1N O T N E C E S S A R I LY S T I N KY
AROMATIC COMPOUNDS
![Page 2: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/2.jpg)
2
HISTORICAL SIGNIFICANCE
• Spices and herbs• Desire to synthesize• Deduced rather simple structure• Common• Benzaldehyde• Benzyl alcohol• Toluene
• Oxidation and further rxn yields the parent hydrocarbon• C6H6
![Page 3: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/3.jpg)
3
BENZENE FACTS
• First isolated by Michael Faraday in 1825• Parent HC of aromatic cpds• Stable cpds• Appears unsaturated• Br2 added to it still appears brown unlike other
unsaturated cpds• KMnO4 oxidation uncommon
• Does not undergo typical addition rxns of alkenes
• Substitution• Main rxn of benzene
![Page 4: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/4.jpg)
4
BENZENE FACTS
C6H6 + Br2 C6H5Br + HBrbenzene bromobenzene
C6H6 + Cl2 C6H5Cl + HClbenzene chlorobenzene
• No isomers are produced by either rxn• All six H’s must be chemically equivalent
FeBr3
FeCl3
![Page 5: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/5.jpg)
5
BENZENE FACTS
C6H5Br + Br2 C6H4Br2 + HBrbromobenzene dibromobenzene
• 3 isomers are produced by further addition of Br2
• Same will occur with chlorobenzene• Must be explained by structure of benzene
FeBr3
![Page 6: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/6.jpg)
6
KEKULÉ BENZENE STRUCTURE
• 1865 Friedrich August Kekulé proposed reasonable structure• First to realize that C was tetravalent (needed 4 bonds)• Architect originally
• Suggested conjugated structure of 6 C’s in hexagonal shape with 1 H on each C• To account for lack of positive tests for
unsaturation, proposed that single and double bonds exchange positions rapidly
![Page 7: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/7.jpg)
7
KEKULÉ BENZENE STRUCTURE
Write the equation for the rxn of benzene and bromine using a Kekulé structure.
![Page 8: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/8.jpg)
8
RESONANCE BENZENE MODEL
• Kekulé not entirely correct• His structures differ only in arrangement of
electrons• Atoms occupy same positions• This is resonance• No equilibrium arrows• Resonance double-headed arrow instead
![Page 9: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/9.jpg)
9
RESONANCE BENZENE MODEL
• No single or double bonds btw C’s in benzene• Planar• All C-C lengths are the same: 1.39 Å• How does this compare to single and double lengths?• Compare to cyclohexane
![Page 10: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/10.jpg)
10
ORBITAL MODEL OF BENZENE
• All C’s are attached to only 3 other atoms• All C’s are sp2 hybridized• 2 sp2 of one C overlap with 2 similar of another C
to make the bonds that form the hexagon• Other sp2 overlaps with 1s of each H• Perpendicular to each sp2 plane, lay unhybridized
p’s• Those p’s do a side-to-side bond… bond
![Page 11: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/11.jpg)
11
ORBITAL MODEL OF BENZENE
• Notice p orbitals do not lie in plane of bonded sp2 and 1s orbitals
![Page 12: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/12.jpg)
12
SYMBOLS FOR BENZENE
• Kekulé structure…keeps electrons clearly in mind• 2 delocalized representations• H’s not usually written in either
![Page 13: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/13.jpg)
13
NOMENCLATURE OF AROMATICS
• Preceded systematic nomenclature• Historic names are respected and accepted by
IUPAC• Several important aromatics that need to be
committed to memory
![Page 14: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/14.jpg)
14
NOMENCLATURE OF AROMATICS
benzene toluene cumene styrenephenol
anisole benzaldehyde acetophenone benzoic acidaniline
CH3CH3CH3 CH2
OH
OCH3 O
OCH3 OOHNH2
![Page 15: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/15.jpg)
15
NOMENCLATURE OF AROMATICS
• Monosubstituted benzenes w/o common names accepted by IUPAC named with benzene as the root chain
bromobenzene nitrobenzene ethylbenzene propylbenzene
BrCH3
CH3
N+ O
-O
![Page 16: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/16.jpg)
16
NOMENCLATURE OF AROMATICS
• When 2 substituents, 3 isomers are possible• 1,2, ortho-, o-• 1,3, ,meta, m-• 1,4, para, p-
ortho-dichlorobenzene meta-dichlorobenzene para-dichlorobenzene(o-dichlorobenzene) (m-dichlorobenzene) (p-dichlorobenzene)(1,2-dichlorobenzene) (1,3-dichlorobenzene) (1,4-dichlorobenzene)
Cl
Cl
Cl
Cl
Cl
Cl
![Page 17: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/17.jpg)
17
NOMENCLATURE OF AROMATICS
• Benzene with 2 methyl groups is called xylene
o-xylene p-xylene
• When 2 substituents are not identical, o-, m-, p- are still used• Substituents are alphabetized where appropriate
• With 3 substituents, normal IUPAC rules
CH3
CH3
CH3
CH3
![Page 18: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/18.jpg)
18
NOMENCLATURE OF AROMATICS
o-bromochlorobenzene m-nitrotoluene
m-chlorophenol o-ethylaniline p-chlorostyrene
Cl
Br
NH2CH3Cl
OH
Cl
CH2
N+
O-
O
OH
![Page 19: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/19.jpg)
19
NOMENCLATURE OF AROMATICS
• Aromatic HC’s known as arenes (Ar, aryl group)• Ar-R…arylalkane
• Benzene can be a substituent• Known as phenyl group (Ph)
• Another group worth noting• Known as benzyl group
R
R
![Page 20: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/20.jpg)
20
NOMENCLATURE OF AROMATICS
2-phenylpentane phenylcyclopropane 1,3,5-triphenylbenzene(2-pentylbenzene) (cyclopropylbenzene)
biphenyl benzyl chloride m-nitrobenzyl alcohol
CH3
CH3
Cl
OH
N+
O-
O
![Page 21: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/21.jpg)
21
RESONANCE ENERGY OF BENZENE
• Resonance hybrid more stable than any contributing structures…proven by benzene’s hybrid structure• Hydrogenation of C=C bond is exothermic and
releases 109-125 kJ/mol• C=C + H-H C-C + 109-125 kJ
• + H-H + 119.5 kJ
![Page 22: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/22.jpg)
22
RESONANCE ENERGY OF BENZENE
• Two C=C bonds broken should release 2x the amount of 1 bond
• + 2 H-H + 239 kJ
• Thus, three C=C bonds should release 3x
• + 3 H-H + 208 kJ
• Benzene proves more difficult to hydrogenate, than simple alkenes
![Page 23: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/23.jpg)
23
RESONANCE ENERGY OF BENZENE
• Therefore, the resonance hybrid structure is more stable (by >150 kJ) than any contributing structure proposed by Kekulé• Difference in hypothesized energy and actual
energy is known as resonance energy• Aromatic cpds tend to preserve their aromatic
structures and thus preserve their resonance energy
![Page 24: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/24.jpg)
24
ELECTROPHILIC AROMATIC SUBSTITUTION
• Most common rxn• Replaces 1 H in the ring
• Chlorination: + Cl2 + HCl
• Nitration: + HNO3 + H2O
• Sulfonation: + H2SO4 + H2O
FeCl3
S
OH
O O
Cl
H2SO4
SO3
N+
O-
O
![Page 25: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/25.jpg)
25
ELECTROPHILIC AROMATIC SUBSTITUTION
• Alkylation: + RCl + HCl
• Alkylation: + CH2=CH2
• Acylation: + + HCl
AlCl3
H2SO4
AlCl3
R
CH3
R
O
R
Cl
O
![Page 26: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/26.jpg)
26
MECHANISM OF ELECTROPHILIC AROMATIC SUBSTITUTION
• Most of the previously illustrated substitution rxns involve initial attack by an electrophile on the benzene ring• Consider the chlorination rxn
+ Cl2 + HCl
• Without the catalyst, the rxn occurs very slowly.• The catalyst acts as a Lewis acid, converting Cl2
to a strong electrophile
FeCl3Cl
![Page 27: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/27.jpg)
27
MECHANISM OF ELECTROPHILIC AROMATIC SUBSTITUTION
Cl ClCl—Cl + Fe—Cl Cl∙∙∙∙∙Cl∙∙∙∙∙Fe—Cl
Cl Clweak strong electrophileelectrophile
+ Cl—Cl∙∙∙∙∙FeCl3 + FeCl4
benzonium ion
Cl
H
![Page 28: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/28.jpg)
28
MECHANISM OF ELECTROPHILIC AROMATIC SUBSTITUTION
• Resulting carbocation is benzonium ion• Positive charge is delocalized by resonance in an
ortho and para manner to the sp3 hybridized C
• Composite illustration of resonance hybrid of benzonium ion
so…sp3 C loses a proton Cl- + HCl
Cl
H
Cl
H
Cl
H
Cl
H
Cl
H
Cl
![Page 29: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/29.jpg)
29
MECHANISM OF ELECTROPHILIC AROMATIC SUBSTITUTION
• Generalizing this 2-step mechanism yields:
+ E+ + H+
• In step 1, resonance energy is lost as pi bond is disrupted as electrophile attaches to a C in ring
• In step 2, resonance energy is regained with loss of proton (H+)
• Step 1 is slow since it requires so much energy (Ea), thus is rate-determining step
• Step 2 is fast with low Ea
EE
Hstep 1 step 2
![Page 30: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/30.jpg)
30
MECHANISM OF HALOGENATION
• Cl and Br easily react as seen• Halogen added slowly to mixture of aromatic cpd
and Fe filings• Fe filings react with halogen to make catalyst,
iron halide• F and I substitution are possible, but require other
methods
![Page 31: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/31.jpg)
31
MECHANISM OF NITRATION
• Nitric acid is protonated by sulfuric acid• Protonated nitric acid loses water and makes
nitronium ion, a very strong electrophile
+
nitric acid protonated nitric acid nitronium ion
N+
O-
O
O
HH+
N+
O-
O
O+
H
H
N+
O
O
O
H
H
![Page 32: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/32.jpg)
32
MECHANISM OF SULFONATION
• Concentrated sulfuric acid catalyst• Strong electrophile is either sulfur trioxide, SO3, or
protonated sulfur trioxide, HSO3+
• SO3 is a strong electrophile at S
benzenesulfonic acid phenol
• Sulfonic acids are products; these are strong organic acids
• If base is added, phenol is formed
S
O
OOH
OH
SO3
H2SO4
NaOH
200°C
![Page 33: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/33.jpg)
33
MECHANISM OF ALKYLATIONAND ACYLATION
• Alkylation and acylation of benzene known as Friedel-Crafts rxns• In alkylation carbocation is electrophile• Formed by removing halide from alkyl halide with Lewis
acid catalyst (i.e. AlCl3)
• Or formed by adding proton to an alkene
• Cannot occur if benzene already has nitro or sulfonic acid group• In acylations acyl cation is electrophile• Generated from acid derivative, usually acyl halide• Makes aromatic ketones
![Page 34: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/34.jpg)
34
MECHANISM OF ALKYLATION
Cl Cl
Cl—Al + ClCH2CH3 Cl—Al—Cl + CH2CH3
Cl Cl ethyl cation
CH2=CH2 CH2CH3
ethyl cation
H+
![Page 35: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/35.jpg)
35
MECHANISM OF ALKYLATION
+ CH2CH3
ethyl cation
ethylbenzene
H+
CH3
H
CH3
H
CH3
H
CH3
![Page 36: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/36.jpg)
36
MECHANISM OF ACYLATION
O
CH3CCl + AlCl3 CH3C=O + AlCl4-
acetyl chloride acyl cation
+ CH3C=O
acetophenone
CH3
HO
CH3
O
H+
![Page 37: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/37.jpg)
37
RING-ACTIVATING VS RING-DEACTIVATING SUBSTITUENTS
• Electron-seeking substituents increase rxn rate• Hydroxyl (-OH)…phenol• Methyl (-CH3)…methylbenzene
• Electron-withdrawing substituents decrease rxn rate• Chloro (--Cl)…chlorobenzene• Nitro (-NO2)…nitrobenzene
![Page 38: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/38.jpg)
38
ORTHO, PARA-DIRECTING VS META-DIRECTING SUBSTITUENTS
• Substituents already present on a ring determine the position taken by a new substituent• Some are ortho,para-directing• Amino, hydroxy, alkyl, halo
• Some are meta-directing• Acyl, carboxyl, nitro
• Important to know which it is due to desired products• Bromobenzene that is nitrated makes o- and p-
bromonitrobenzene• Nitrobenzene that is brominated makes m-
bromonitrobenzene
![Page 39: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/39.jpg)
39
POLYCYCLIC AROMATIC HYDROCARBONS
• Aromaticity…unusual stability of certain fully conjugated cyclic systems…beyond benzene• Naphthalene, C10H8, first pure cpd isolated from a
by-product of converting coal to coke
• C’s are numbered to indicate 3 sets of equivalent C’s• BL’s are not all the same, but close to 1.39 Å• RE < 2x that of benzene 251 kJ/mol• Undergoes electrophilic substitution, with
monosubstitution predominantly at C-1
1
2
3
44a
5
6
7
88a
![Page 40: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/40.jpg)
40
NITRATION OF NAPHTHALENE AT C-1
• Four contributors are possible…
• Draw the contributors for nitration at C-2. Why is C-1 preferred?
HN+
O-
OH
N+
O-
O
HN+
O-
OHN+
O-
O
![Page 41: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/41.jpg)
41
FUSED POLYCYCLIC HYDROCARBONS
anthracene phenanthrene pyrene
• PAH’s make up a large percentage of the C found in interstellar space• Observed in interstellar ice (Halley’s comet)• UV radiation of PAH’s in ice yield aromatic ketones,
alcohols, and other cpds—prebiotic chemistry role?!
![Page 42: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/42.jpg)
42
![Page 43: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/43.jpg)
43
![Page 44: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/44.jpg)
44
![Page 45: 1 NOT NECESSARILY STINKY AROMATIC COMPOUNDS. HISTORICAL SIGNIFICANCE Spices and herbs Desire to synthesize Deduced rather simple structure Common Benzaldehyde](https://reader030.vdocuments.net/reader030/viewer/2022032703/56649d175503460f949ed010/html5/thumbnails/45.jpg)
45