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*1/ With the BLW code calculate the relative energies of the three Lewis structures of the allyl cation at the HF level. By comparison with the energy of the allyl cation, determine the VRE and the ARE. Compare the C-C bond distances.
 
*1/ With the BLW code calculate the relative energies of the three Lewis structures of the allyl cation at the HF level. By comparison with the energy of the allyl cation, determine the VRE and the ARE. Compare the C-C bond distances.
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!'''Hints'''
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* Starting from the delocalized geometry, the first iteration of the optimization of the localized structure will give the VRE.
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*2/ Repeat the first question at the B3LYP level.
 
*2/ Repeat the first question at the B3LYP level.
  
 
*3/ Repeat questions 1 and 2 for the allyl radical.
 
*3/ Repeat questions 1 and 2 for the allyl radical.
 
*4/ With XMVB, for the allyl cation put in resonance  structures '''I''' and '''II''', then add  structure '''III'''. What is the gain in energy due to the inclusion of this third structure?
 
  
 
[[VBFile 4-2 | FILES FOR THE ALLYLS]]
 
[[VBFile 4-2 | FILES FOR THE ALLYLS]]
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  don't forget to name the cube file.   
 
  don't forget to name the cube file.   
 
  '''test.cube_BLW'''  
 
  '''test.cube_BLW'''  
  see also [[VBFile_4-4#gaussiancube.com | gaussiancube file]]
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  see also [[VBFile_4-3#gaussiancube.com | gaussiancube file]]
  
 
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[[VBFile 4-4 | FILES FOR THE NH3 ... BH3]]
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[[VBFile 4-3 | FILES FOR THE NH3 ... BH3]]
  
 
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* Use the perpendicular form given below to compute the "deconjugated" system. The comparairison with the planar standard calculation gives an estimate of the conjugaison, which is contaminated by some hyperconjugaison.
 
* Use the perpendicular form given below to compute the "deconjugated" system. The comparairison with the planar standard calculation gives an estimate of the conjugaison, which is contaminated by some hyperconjugaison.
* To inhibit hyperconjugaison in the perpendicular form, localize the electron on the C1=C2 and on C3=C4 double bond. (note that the C3=C4 vinyl group has rotated along the XZ plane; hence its pi system is along the Y axis.
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* To inhibit hyperconjugaison in the perpendicular form, localize the electrons on the C1=C2 and on C3=C4 double bond. (note that the C3=C4 vinyl group has rotated along the XZ plane; hence its pi system is along the Y axis.
  
 
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[[File:Rotated_butadiene.png|right|250px|alt=butadiene - Lewis alt text | planar butadiene The C3=C4 has rotated along the XZ plane; hence its pi system is along the Y axis.]]<html><pre>
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<html><pre>
 
  C    6.0  0.000000  -1.086858    2.236154
 
  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    1.489418
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</pre></html>
 
</pre></html>
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[[File:Rotated_butadiene.png|right|250px|alt=butadiene - Lewis alt text | planar butadiene The C3=C4 has rotated along the XZ plane; hence its pi system is along the Y axis.]]
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[[VBFile 4-4 | FILES FOR THE BUTADIENE DECONJUGAISON ]]
 
[[VBFile 4-4 | FILES FOR THE BUTADIENE DECONJUGAISON ]]
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<math> \Psi_{HL-CI}=0.81\Psi_{I}+0.58\Psi_{II}</math>, hence the weights of the structures (I/II)=(66%/34%)  
 
<math> \Psi_{HL-CI}=0.81\Psi_{I}+0.58\Psi_{II}</math>, hence the weights of the structures (I/II)=(66%/34%)  
  
Note that in HL-CI <math><Psi_{I}|\Psi_{II}>=0</math>
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Note that in HL-CI <math><\Psi_{I}|\Psi_{II}>=0</math>
 
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Dernière version du 14 février 2013 à 08:27

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BLW method & HuLiS program