Matriculation Chemistry Introduction to Organic Compound part 1.pdf
Matriculation Chemistry Aromatic Compound
Transcript of Matriculation Chemistry Aromatic Compound
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The origin of August Kekulé’s view of benzene structure:
“There I sat and wrote mytetbook! but things did notgo well" my mind wasoccu#iedwith other matters! I turnedthe
chair towards the fire#laceandbegan to doze$
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“%nce again the atoms dancedbefore my eyes$ This timesmaller grou#s modestly
remained in the background$&y mental eye! shar#ened byre#eated a##aritions of similar kind! now distinguished larger
units of various sha#es$'
“(ong rows! fre)uently *oined more densely" everything inmotion! twisting and turninglike snakes$ And behold! whatwas that+ %ne of the snakescaught hold of its own tail andmockingly whirled around my
eyes$
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“, awoke! as if by lightening"
this time! too! I s#ent the rest ofthe night working out theconse)uences of thishy#othesis'
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“(et us learn to dream! gentlemen! then #erha#s we shall find the truth'
A-.-/T K0K-(1
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0dison! 0instein and many others have used thesubconscious mind to give them the insight and the
“know2how' to bring about their great achievements$
August Kekulé
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“In variably! my device works as I imagined it should$
In twenty years there has not been
single ece#tion$' 3IK%(A T0/(A
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“Imagination is more im#ortant than knowledge$'
A(405T 0I3/T0I3
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A5%&ATI6 6%&7%-38/
Introduction toaromatic 6om#ounds
,9$,
Arenes aromatic com#ounds:
the word aromatic has nothing to do with odour $
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Kekulé structure
resonance structure
aromatic
ortho meta #ara
;riedel26raft acylationelectro#hilic substitution
activating anddeactivating grou#
ortho2#ara and meta director
oidation of
alkylbenzene
substitution of
toluene
K0<=%58/
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,>?@ &ichael ;araday4ritishB
Isolated a #ure com#ound of
boiling #oint >Co6
0m#irical formula 6D
3amed “bicarburet of hydrogen'
8I/6%E05< %; 403F030
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,>G9 0ilhard &itscherlich .ermanB
7re#ared benzene from benzoic acid6HD@6%?D 6a% 6HDH 6a6%G
heat
&olar mass J>! molecular formula 6HDH
named “benzin'
benzene benzin benzoin
ben*oin;renchB
gum benzoin (uban awiArabicB
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,>HH ;riedrich August Kekulé .ermanB
7ro#osed a cyclic structure for benzene$
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In earlier time! com#ounds are called aromatic because of their #leasant odours$
Today! we use the word aromatic to refer to
benzene and its structural relatives$
4enzene has strong
#leasant odour $
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6
66
66
6
D
D
D
D
D
D
or
K0K-(1’/ /T5-6T-50
Kekule was the first to formulate areasonable re#resentation of benzene
The Kekule structure suggests alternating doubleand single carbon2carbon bonds
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The si π electrons com#letely delocalized around the ring
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All si 6 atoms and si p orbitals are e)uivalent
The circle re#resents the siπ electrons! distributed over
the si atoms of the ringN
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TD0 65IT05IA ;%5 A5%&ATI6IT<
9 structural criteria must be satisfied forcom#ound to be aromatic
6 o m # l e t e l y
c o n * u g a t e d
6 y c l i c 7 l a
nar
6 o n t a i n # a r t i c u l a r n u m b e r o f ∏ e l e c t r o n o b e y s D Ü c k e l ’ s 5 u l e
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TD0 65IT05IA ;%5 A5%&ATI6IT<
%-/% -35 5-6789
:en;ene
,$ Aromatic com#ounds with a single ring
[4n+2] ∏ = [4(1 + 2]∏
= # ∏ electrons
aromatic
:en;ene is aromatic !ecause<
contains #∏ electrons
(obeys HÜc'els ule
cyclic, planar and has dou!le
!ond in the ring
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TD0 65IT05IA ;%5 A5%&ATI6IT<
?$ Aromatic com#ounds with more than one ring
na#hthalene
4n+2= 4(2+ 2 10 ∏ electrons
romatic
3"o !en;ene rings joined together $orms naphthalene
%-/%
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A5%&ATI6 6%&7%-38/
3omenclature of benzene and its derivatives,9$?
Arenes aromatic com#ounds:
the word aromatic has nothing to do with odour $
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3A&I3. 403F030 805IEATIE0/
&any organic molecules contain a benzene ring with one or more substituents$
&any common name arerecognized by the I-7A6system
6DG
6ommon: tolueneI-7A6: methylbenzene
0OA&7(0:
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4enzene is the #arent name and the substituent
is indicated by a #refi$
;
fluorobenzene
6l
chlorobenzene
4r
bromobenzene
3%?
nitrobenzene
6D?6DG
ethylbenzene
&%3% /-4/TIT-T08 403F030
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I-7A6 rules allow some common names to be retained$
6DG
toluene
%D
#henol
3D?
aniline
6%%D
benzoic acid
6D%
benzaldehyde
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5elative #osition of subsituents are indicated by #refies ortho! meta! and para o L! m L! and p LB
or by the use of number $
4r
4r , ?
,!?Ldibromobenzeneor
o Ldibromobenzene
4r
4r
,?
G
,!GLdibromobenzeneor
m Ldibromobenzene
4r
4r
,!9Ldibromobenzeneor
p Ldibromobenzene
,?
G9
8I/-4/TIT-T08 403F030
3"o 9ame 9u!stituents
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6%%D3%?
,?
?Lnitrobenzoic acidor
o Lnitrobenzoic acid
,?
G
GLnitrobenzoic acidor
m Lnitrobenzoic acid
6%%D
3%?
9Lnitrobenzoic acidor
p Lnitrobenzoic acid
, ?
G9
6%%D
3%?
/elect one of the substituent that givenew #arent name and numbered as 6,$
8I/-4/TIT-T08 403F030
3"o 8i$$erent 9u!stituents
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7osition of substituents must be indicated bynumbers$
4r
4r
4r
, ?
G9
,!?!9Ltribromobenzene
The substituents are listed al#habetically when writing the name$
6l
4r
I?LbromoL,LchloroLGLiodobenzene
TD500 %5 &%50 /-4/TIT-03T/
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6 atom bearing the subtituent that define thenew #arent name is numbered as 6,$
%D
3%?
3%?
?!9Ldinitro#henol
D% %D
6%%D,
?
G
9
,?
G
9
@
H
G!@Ldihydroybenzoic acid
4r
6DG
6DG
,
?G9
9LbromoL,!?Ldimethylbenzene
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4r
6DG
6DG
,
?G
9
9LbromoL,!?Ldimethylbenzene
o L! m L and p L naming system is usedfor arenes with ? substituents onlyN
9LbromoLo Ldimethylbenzene
correct
14 2-11
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If alkyl substituent is larger than the ringmore than H 6B! the com#ound is named as
#henyl2substituted alkane$
6DL6D? L6D? L6D? L6D? L6DG
6D?,
?G 9 @ H J
?L#henylhe#tane
14.2 11
7D03<( .5%-7
4enzene ring as substituent$
7henyl 6HD@ L 7h
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A5%&ATI6 6%&7%-38/
6hemical #ro#erties of benzeneand its derivatives
,9$G
Arenes aromatic com#ounds:
the word aromatic has nothing to do with odour $
14.3-01
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403F030
4r ? S 66l9 no addition of 4r ?no decolorizationB
K&n%9 S D?% no oidation
no decolorizationBD? S 3islow addition at hightem#erature and #ressure
-3-/-A( 50A6TI%3/ %; 403F03014.3 01
Alkenes readily undergo additionreaction! benzene does notN
14 3-03
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Involves substituents attached to the ring
0lectro#hilic aromatic substitution
4r ?;e4r G
4r
benzene bromobenzene
Involves the benzene ring itself
6DG6D?6D?6DG K&n%9
D?%
6%%D
butylbenzene benzoic acid
50A6TI%3 %; A5030/ 14.3 03
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14.3-05
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OO?! ;eOG
O 6l 4rB DOhalogenatio
n
D%3%?
D?/%9
3%?
D?%nitratio
n
56l ! Al6lG
5 can rearrangeB
5 D6l
;riedel26raftsAlkylation
566l ! Al6lG
%
6L5%
D6l
;riedel26raftsAcylation
14.3 05
14.3-07
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/T07 , ;ormation of arenium ion
D
D
D
D
D
D 0
D
D
D
D
0D
D
D D
D
D
0D
D
D
D
D
D
D
0D
.0305A( &06DA3I/&14.3 07
arenium ion
14.3-08
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0
0lectro#hile takes two electrons of siLelectronsπ system to form σ bond$
benzene ring
This interru#ts of cyclic system of π electrons$
4enzene ring arenium ion aromaticB nonaromaticB
The four π electrons delocalized through these
the five 6 atom p orbitalsB
0
D
arenium ion
A503I-& I%314.3 08
14.3-09
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/T07 ? (oss of D
D
D
D
D
D
0D
D
D
D
D
0
D
0D
0
H π electrons 9 π electrons
0 L D
H π electrons
/ubstitution reaction allowaromatic si π electrons to
be regenerated$
14.3 09
14.3-10
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Kekulé structures are more a##ro#riate for writing
mechanisms$ ;or sim#licity! however! we can show the mechanism
in the following way:
/T07 ,
0
0
D
arenium ion
/T07 ? 0
D
0
D
14.3-11
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4r
4r ?no reactiondecolorization not observedB
4r ?;e4r G
bromobenzene
D4r
DA(%.03ATI%3
5eactants: benzene and halogens 6l? or 4r ?B$
6onditions:
(ewis acid such as ;e6lG and ;e4r G
14.2-13
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/T07 , ;ormation of 4r
4r L4r ;e4r G 4r R4rL;e4r G L
4r ;e4r 9 L
com#le
4r
/T07 ? ;ormation of arenium ion
/T07 G (oss of D
4r
D4r
&06DA3I/&
;e4r 9 L
;e4r G
4r D
4r
D
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12.5-49
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/T07 , ;ormation of nitronium ion 3%?B
D?% 3%?
&06DA3I/&
D
. .
. .
D2%23%? D2%/%GD D2%23%? D/%9 L..
nitronium ion
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3%?
/T07 ? ;ormation of arenium ion
/T07 G (oss of D
3%?
D?/%9
D/%9 L
3%?
D
3%?
D
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12.5-52
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6D6DGB?
/T07 ? ;ormation of arenium ion
/T07 G (oss of D
6D6DG
B?
D6l
Al6l9 L
6D6DGB?
D
6D6DGB?
D
%TD05 ;A6T/ A4%-T 12.5-55
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5earrangement can occur! es#ecially when
,o haloalkanes are used$
0OA&7(0:
6DG6D?6D?6D?6l
6D?6D?6D?6DG
butylbenzene
6D6D?6DG
6DG
sec Lbutylbenzene
H@
G@
5earrangement:
6DGR6D?R6DR6D?
D
,o carbocation
6DGR6D?R6DR6DG
?o carbocation
Al6lG
%TD05 ;A6T/ A4%-T;5I080(L65A;T A(K<(ATI%3
;5I080( 65A;T A6<(ATI%312.5-56
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0OA&7(0:
6DG6R6l%
acetyl chloride
Al6lG66DG
%
aceto#henone
D6l
;5I080(L65A;T A6<(ATI%3
5eactants: benzene and acid chloride$
6onditions:
6atalyst: (ewis acid such as Al6lG$
7roduct: ketone$
A6<( .5%-712.5-57
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0OA&7(0:
6DG6R
%
acyl grou#
benzoyl grou#
L6R
%
56R%
acetyl grou#
A6<( .5%-7
Acylation transfer anacyl grou# to benzene
&06DA3I/&12.5-59
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/T07 , ;ormation of acylium ion
acylium ion
5L6L6l Al6lG 5L6L6lLAl6lG
:%: :%:
5L6 P % 5L6Q% Al6l9 L
&06DA3I/&
:
:
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5L6 P%
/T07 ? ;ormation of arenium ion
/T07 G (oss of D
D6l6P%
5
6%
D
5
6%
D
5 Al6l9 L
/-4/TIT-03T 0;;06T12.5-61
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4ut! what would ha##en if we were to carry out a reactionon aromatic ring that already has a substituent+
/-4/TIT-03T 0;;06T
0;;06T %3 50A6TIEIT<12.5-62
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Activating grou#s:
/ubstituents that activate the ring!making it more reactive than benzene$
3%? 6l D %D
relative rateof nitration
0OA&7(0:
H ,C L> C$CGG , ,CCC
reactivity
0;;06T %3 50A6TIEIT<
8eactivating grou#s:
/ubstituents that deactivate the ring!making it less reactive than benzene$
0;;06T %3 %5I03TATI%312.5-63
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0OA&7(0:
6DG
D3%G
D?/%9
6DG
3%?
6DG
3%?
6DG
3%?
@MB GJ
9
ortho2#ara director
%rthoL#ara directors
0;;06T %3 %5I03TATI%3
&eta directors
Tend to direct the incoming grou# intoortho and #ara #ositions$
Tend to direct the incoming grou# intometa #osition$
6(A//I;I6ATI%3 %; /-4/TIT-03T/12.5-64
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6(A//I;I6ATI%3 %; /-4/TIT-03T/
ortho L ! para L directingactivators
ortho L ! para L directingdeactivators
meta L directing deactivators
%5TD%L ! 7A5AL 12.5-65
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!8I506TI3. A6TIEAT%5/
R3D?
●●
R5
R3D6%5●●
R%5●●
●●
R%D
●●
●●
R3D5●●
R35?
●●
Increasing activation
.eneralstructure:R5 or RF
●●
Alkyl grou#s or havenonbonded electron #air on the atom bonded to
benzene ring
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0OA&7(0:
6D?6DG
4r ?
;e4r G
6D?6DG
4r
6D?6DG
4r G>B
ethylbenzene H?B
%5TD%L ! 7A5AL 12.5-67
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!8I506TI3. 80A6TIEAT%5/
R;●●
●●
●●
R6l●●
●●
●●
R4r ●●
●●
●●
R I●●
●●
●●
.eneral structure
RO halogensB
●●
●●
●●
12.5-68
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0OA&7(0:
6l
D3%G
D?/%9
6l
3%?
6l
3%?
G@Bchlorobenzene
H9B
&0TA 8I506TI3. A6TIEAT%5/12.5-69
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&0TAL 8I506TI3. A6TIEAT%5/
R6D%
Increasing deactivation
.eneralstructure:R< or LB
R6%5
R6%%5
R6%%DR63
R/%GD
R3%?
R35G
Dave a full or #artial#ositive charge on the
atom bonded tobenzene ring
0OA&7(0
12.5-69
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0OA&7(0:
3%?
D3%G
D?/%9
nitrobenzene
3%?
3%?MGB
I38-6TIE0 0;;06T12.5-70
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8ue to:
I38-6TIE0 0;;06T
0lectronegativity of the atoms in thesubstituent$
7olarisability of the substituent$
0OA&7(0:
6l
6lR electronLwithdrawing
6DG
6DGR electronLdonating
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Activating .rou#s
5elease electrons to the ring /tabilise arenium ion
;orm faster
6DG
8eactivating .rou#s
=ithdraw electrons from the ring
8estabilise arenium ion
;orm slower
3%?
6l
3%?
0OA&7(0:12.5-72
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6;G
trifluoromethylBbenzene benzene
6DG
toluene increasing rate of nitration
6;G withdraws e2! arenium ion less stable
ring less reactive
6DG releases e2! arenium ion more stable
ring more reactive
6;G
3%?
3%?6DG
3%?
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0OA&7(0: 12.5-76
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6DG
toluene
K&n%9
heat
6%%D
6DG%?3
p Lnitrotoluene
3a?6r ?%J
heat6%%D%?3
p Lnitrobenzoic acid
6D6DGB?6DG 6%%DD%%6
K&n%9
heat
benzoic acid
iso#ro#yl toluene tere#ththalic acid
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DA(%.03ATI%3 %; T%(-03012.5-78
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Take #lace at high tem#erature or in the#resence of uv light$
&echanism: freeLradical substitution
6l or 4r re#laces D atom of alkyl grou#
6DG
6l?
heat orlight
6D?6l
0OA&7(0:
6l?
heat orlight
6D6l?6l?
heat orlight
66lG
toluene benzyl chloride
dichloromethylBbenzene
trichloromethylBbenzene
DA(%.03ATI%3 %; T%(-030
ree radical su!stitution reaction
DA(%.03ATI%3 %; T%(-030
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DA(%.03ATI%3 %; T%(-030
%lectrophilic aromatic su!stitution reaction
6DG
toluene
4r ?
;e4r G
6DG
4r ?
6DG
4r ?
6D?● 12.5-79
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4enzylic radicals are even more stable than Go radicalsN
benzylicradical
6A56I3%.03I6 0;;06T 12.5-34
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&any aromatic com#ounds are carcinorgenic and toic$
6DG
toluenebenzene
6A56I3%.03I6 0;;06T
0am#le: benzene! benzoUaV#yrene$
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At one time! benzene was widely used as solvent$
/tudies revealed benzene is carcinorgenic can cause cancer B$
5e#laced by toluene$
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4enzoUaV#yrene is found in cigarette smoke! automobile ehaust! and the fumes from charcoal grills$
benzoUaV#yrene
=hen ingested or inhaled! it oidised to carcinogenic #roducts$
12.5-21
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4enzoic acid! the sim#lest organic acid! #revent the
growth of many organism$
12.5-22
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widely used as a food #reservative$
12.5-19
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;resh wild berries
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