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{| class="collapsible collapsed wikitable"
 
{| class="collapsible collapsed wikitable"
 
|-
 
|-
!'''Twisted geometry'''
+
!'''Twisted (perpendicular) geometry'''
 
|-
 
|-
 
|
 
|
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   BLW-ED Analysis
 
   BLW-ED Analysis
 
   C1   
 
   C1   
 +
C    6.0  0.000000  -1.086858    2.236154
 +
C    6.0  0.000000    0.000000    1.489418
 
  C    6.0  0.000000    0.000000    0.000000
 
  C    6.0  0.000000    0.000000    0.000000
  C    6.0   0.000000   0.000000   1.489418
+
  C    6.0 -1.086858   0.000000   -0.746736
 
  H    1.0  0.967527    0.000000  -0.478451
 
  H    1.0  0.967527    0.000000  -0.478451
 
  H    1.0  0.000000    0.967527    1.967869
 
  H    1.0  0.000000    0.967527    1.967869
C    6.0  -1.086858    0.000000  -0.746736
 
C    6.0  0.000000  -1.086858    2.236154
 
 
  H    1.0  -2.072275    0.000000  -0.314213
 
  H    1.0  -2.072275    0.000000  -0.314213
 
  H    1.0  -1.029400    0.000000  -1.820913
 
  H    1.0  -1.029400    0.000000  -1.820913
 
  H    1.0  0.000000  -2.072275    1.803631
 
  H    1.0  0.000000  -2.072275    1.803631
 
  H    1.0  0.000000  -1.029400    3.310331
 
  H    1.0  0.000000  -1.029400    3.310331
$END
+
$END
 +
 
 
</pre></html>
 
</pre></html>
 
|}
 
|}
In the BLW part we localize px-like pi orbitals of atoms C2 and C6 and  py-like orbitals for C1 C5 to avoid hyperconjugaison.
+
In the BLW part we localize px-like pi orbitals of atoms C1=C2 and  py-like orbitals for C3=C4 to avoid hyperconjugaison.
 
{| class="collapsible collapsed wikitable"
 
{| class="collapsible collapsed wikitable"
 
|-
 
|-
!'''BLW-Localized twisted geometry'''
+
!'''BLW-Localized part'''
 
|-
 
|-
 
|<html><pre>
 
|<html><pre>
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  $BLWDAT
 
  $BLWDAT
 
   2 8 0
 
   2 8 0
    4 8 13 15 38 42 47 49
+
  3  7 13 14 18 22 28 29
 
   2 8 0
 
   2 8 0
  18 22 28 29 52 56 62 63
+
34 38 43 45 49 53 58 60
26 56 -1
+
  26 56 -1
$END
+
$END
  
 
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</pre></html>
Ligne 97 : Ligne 98 :
  
 
:We find  
 
:We find  
:delocalized planar -155.8824504889
+
:planar delocalized -155.8824504889
:localized planar -155.8603462862  (13.9 kcal/mol)
+
:planar localized -155.8603462862  (13.9 kcal/mol)
:Twisted       -155.8695790387    ( 8.1 kcal/mol)
+
:Perpendicular       -155.8695790387    ( 8.1 kcal/mol)
:Twisted but local -155.8537320442  (18.0 kcal/mol)
+
:Perpendicular but localized -155.8537320442  (18.0 kcal/mol)
 
Hence conjugaison is 13.9 kcal/mol, and the hyper conjugaison in the twisted form is as large as 9.9 kcal/mol
 
Hence conjugaison is 13.9 kcal/mol, and the hyper conjugaison in the twisted form is as large as 9.9 kcal/mol

Dernière version du 11 juillet 2012 à 17:33

return to Tutorial n°4 Two geometries are provided the planar and the twisted where a vinyl part C1 C5 has been twisted by 90°. this second moieties has its pi orbitals along the y direction.

Evaluation of the conjugaison

Localization of px-like pi orbitals to deconjugate keeping planar

Evaluation of the hyperconjugaison in the twisted form

In the BLW part we localize px-like pi orbitals of atoms C1=C2 and py-like orbitals for C3=C4 to avoid hyperconjugaison.

We find
planar delocalized -155.8824504889
planar localized -155.8603462862 (13.9 kcal/mol)
Perpendicular -155.8695790387 ( 8.1 kcal/mol)
Perpendicular but localized -155.8537320442 (18.0 kcal/mol)

Hence conjugaison is 13.9 kcal/mol, and the hyper conjugaison in the twisted form is as large as 9.9 kcal/mol