Ethylene, trans-1,2-difluoro

As a second example of a 4N + 2 pi electron molecule we consider 1,2 difluoro-ethylene which can exist in a cis and a trans geometry. The dissection employed is shown below ... 

Fig. 24. Stabilizing orbital interactions in cis and trans 1,2-difluoro-l,2-dihydroxy ethylene. Symmetry labels are with respect to a rotational axis (trans isomer) and mirror plane (cis isomer)...

When similarly treated, 2,3-pentanedione gave a mixture of the cis- and trans- isomers of l,2-difluoro-l-ethyl-2-methyl ethylene carbonate [632] ... 

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