VBFile 4-4

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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