20:DIENES ,
CONJUGATED SYSTEMS & PERICYCLIC REACTIONS
,
CONJUGATED SYSTEMS :
p-orbitals overlap across
·
single bonds
X
與…
examples :
·
bonds are I
㎥
- ap xx ≈
o
ーーー
_
unconjugated Conjugated cumulated
* Hi = -
61 kcal/mol -
541 keal/mol 7 D Leal/mol
-
Stability : most stable least stable
RELATIVE STABILITY OF ALLENES ,
DIENES , & POLYENES :
ww
. aimn
. . "
isolated alkene isolated diene conjugated polyene
least Stable most stable
diene
TU-MOLECULAR ORBITAL (MO) DIAGTRAMS :
number of atomic orbitals combined
888 8
·
113 butadiene .이 -
orbitalslo
-
3
β p
.
' -3
… -
molecular orbitals
=
number of molecular orbitals created
posit
~
plans
-I nodal entibondingMos -node : a point or plane of zero electron
density in an orbital
& 0 ddd
÷
∵33sfinianpiansnrdatplann
(
'
…
← - -
molecular orbitals)
… …
MOS
题?
{ … uo
.
molecular orbitals (
iv , -O nodal plaes
bonding MO s
, delocalized lone pair
·
allyl anion
#GORO sp- orbital
3 it-molecular orbitals
( To-electrons (
~ >- LUMO
-Big o
- - - - - - - - - -
NON-BONDING ENERGY LEVEL
↑ delocalized lone pair (resonance)
TA , delocalized it bond (resonance
THERMODYNAMIC US KINETIC PRODUCTS IN RXN OF HX
. ( & X2) WICONJUGATED DIENES :
·
addition of HBr to 1,3-butadiene
.
HBr
"
→ t
23
- therm .
≈ " ' Br
1
- Z -
↓
1 2 addition 1 4 addition
, ,
"
kinetic ·
thermodynamic
: forms faster ·
more stable (i bond more sub)
nigmrtssymmsom
I tnrwinma
·
mechanism
i
ommmwt
"
6
I
-
I
. (406) nigu temp.
. -
r
2
/Bu
.
RXN Coordinate
Dadition of HBr to isoprene
·
HBr L.
e
(1 , 2) (1 , 4)
「 HBS ? *
2
Br
I
坐 w I →÷ ]
← t
- Br
,
Linetic (78%) thermodynamic (40 )
%
·
Br attacks faster ·
it bund more stable
·
more substituted transition state takes
priority
Kinetic : X attacks faster but less stable (78 %)
·
·
thermodynamic : To bond is most sub but run is slower (40%)
, O PERICYCLIC RXN
FRONTIER MOLECULAR THEORY :
concerted (single step)
· ·
pericyclic reaction
]
cyclic transition state bond orbitals
·
I:
:
Komaakiiom ↑ "
_
I Overlap in a continuous
cycle
no ionic or radical int
·
.
·
pericyclic reaction theory
=
、8&O
rmHmsMhmoaeoMootonereaccans
—室善善喜 _ — ·
supraficial collision geometry
phasing needs to match
?
哨晶 {
Mnodomour 護theherreacdant UMJO 6
where orbital contact occurs
= hnuq1
DIELS-ALDER REACTION (pericyClic) :
· อ
·
examples ·
Diene must be able to assume s-cis conf.
,
-
≈ …
I
X
*
*
□ ]
… - ≈1
→ -
+· electron
conjugated cyclo nexene product
·
·
diene Defficient s-trans S-Cis
alkene
(O , Et XE] ,
E I。
S-cis locked in
I I1
+ 、
·
conjugated ·
COzEt
electron ·
cyclo nexene product
TT
-Y
②
diene Defficient
cannot undergo DAR
alkyne
·
more substituents= faster rate + lower temp ED(T ENC
-R alkul
( ) S yR
-
Ee t
ooocpressure
2
1 →
5 -R ㆍ -
OHIR
·
อ ↓
. E" ' " *
…
'
J
Anir ( ครอบ
! electron rich electron
LUM8 K I
一
一
dlefficient
SiN
CONJUGATED SYSTEMS & PERICYCLIC REACTIONS
,
CONJUGATED SYSTEMS :
p-orbitals overlap across
·
single bonds
X
與…
examples :
·
bonds are I
㎥
- ap xx ≈
o
ーーー
_
unconjugated Conjugated cumulated
* Hi = -
61 kcal/mol -
541 keal/mol 7 D Leal/mol
-
Stability : most stable least stable
RELATIVE STABILITY OF ALLENES ,
DIENES , & POLYENES :
ww
. aimn
. . "
isolated alkene isolated diene conjugated polyene
least Stable most stable
diene
TU-MOLECULAR ORBITAL (MO) DIAGTRAMS :
number of atomic orbitals combined
888 8
·
113 butadiene .이 -
orbitalslo
-
3
β p
.
' -3
… -
molecular orbitals
=
number of molecular orbitals created
posit
~
plans
-I nodal entibondingMos -node : a point or plane of zero electron
density in an orbital
& 0 ddd
÷
∵33sfinianpiansnrdatplann
(
'
…
← - -
molecular orbitals)
… …
MOS
题?
{ … uo
.
molecular orbitals (
iv , -O nodal plaes
bonding MO s
, delocalized lone pair
·
allyl anion
#GORO sp- orbital
3 it-molecular orbitals
( To-electrons (
~ >- LUMO
-Big o
- - - - - - - - - -
NON-BONDING ENERGY LEVEL
↑ delocalized lone pair (resonance)
TA , delocalized it bond (resonance
THERMODYNAMIC US KINETIC PRODUCTS IN RXN OF HX
. ( & X2) WICONJUGATED DIENES :
·
addition of HBr to 1,3-butadiene
.
HBr
"
→ t
23
- therm .
≈ " ' Br
1
- Z -
↓
1 2 addition 1 4 addition
, ,
"
kinetic ·
thermodynamic
: forms faster ·
more stable (i bond more sub)
nigmrtssymmsom
I tnrwinma
·
mechanism
i
ommmwt
"
6
I
-
I
. (406) nigu temp.
. -
r
2
/Bu
.
RXN Coordinate
Dadition of HBr to isoprene
·
HBr L.
e
(1 , 2) (1 , 4)
「 HBS ? *
2
Br
I
坐 w I →÷ ]
← t
- Br
,
Linetic (78%) thermodynamic (40 )
%
·
Br attacks faster ·
it bund more stable
·
more substituted transition state takes
priority
Kinetic : X attacks faster but less stable (78 %)
·
·
thermodynamic : To bond is most sub but run is slower (40%)
, O PERICYCLIC RXN
FRONTIER MOLECULAR THEORY :
concerted (single step)
· ·
pericyclic reaction
]
cyclic transition state bond orbitals
·
I:
:
Komaakiiom ↑ "
_
I Overlap in a continuous
cycle
no ionic or radical int
·
.
·
pericyclic reaction theory
=
、8&O
rmHmsMhmoaeoMootonereaccans
—室善善喜 _ — ·
supraficial collision geometry
phasing needs to match
?
哨晶 {
Mnodomour 護theherreacdant UMJO 6
where orbital contact occurs
= hnuq1
DIELS-ALDER REACTION (pericyClic) :
· อ
·
examples ·
Diene must be able to assume s-cis conf.
,
-
≈ …
I
X
*
*
□ ]
… - ≈1
→ -
+· electron
conjugated cyclo nexene product
·
·
diene Defficient s-trans S-Cis
alkene
(O , Et XE] ,
E I。
S-cis locked in
I I1
+ 、
·
conjugated ·
COzEt
electron ·
cyclo nexene product
TT
-Y
②
diene Defficient
cannot undergo DAR
alkyne
·
more substituents= faster rate + lower temp ED(T ENC
-R alkul
( ) S yR
-
Ee t
ooocpressure
2
1 →
5 -R ㆍ -
OHIR
·
อ ↓
. E" ' " *
…
'
J
Anir ( ครอบ
! electron rich electron
LUM8 K I
一
一
dlefficient
SiN
