Sp^y orbitals and nature of bonds

[plexus0208]

Homework Statement

1,2-difluoroethylene has two isomers, cis and trans, and they do not interconvert readily.
However, cis and trans isomers of (C6H5)HC=CH(C6H5) do interconvert (but slowly). How is the
intermediate required for that interconversion stabilized by the phenyl groups?

Homework Equations

The Attempt at a Solution

I think it has something to do with the fact that when a single electron is "delocalized" throughout a large π system consisting of alternating C-C and C=C bonds, it leads to lower energy species... but I still don't get it. What is meant by intermediate? (My professor never really went over this part.)

 

[chemisttree]

If you could convert the double bond to a single bond, you could get rotation about the bond before the double bond reforms. How might you accomplish it?

 

[Blueshift5]

I can provide a response to this content by explaining the concept of sp^y orbitals and how they relate to the nature of bonds in molecules. Sp^y orbitals are hybrid orbitals that are formed when s and p orbitals combine to form a new set of orbitals with different properties. These orbitals have a greater directional character compared to pure s or p orbitals, making them ideal for forming bonds with other atoms.

In the case of 1,2-difluoroethylene, the two isomers (cis and trans) have different arrangements of the fluorine atoms around the double bond. This leads to different spatial arrangements of the sp^2 orbitals involved in the double bond, resulting in different bond angles and bond strengths. Due to this difference, the isomers do not interconvert readily.

However, in the case of (C6H5)HC=CH(C6H5), the presence of the phenyl groups (C6H5) stabilizes the intermediate required for interconversion of the cis and trans isomers. This is because the delocalized π system of the phenyl groups allows for the single electron to be spread out over a larger area, resulting in a lower energy state for the intermediate. This stabilization of the intermediate allows for the slow interconversion of the isomers to occur.

In summary, the presence of the phenyl groups in (C6H5)HC=CH(C6H5) stabilizes the intermediate required for the interconversion of cis and trans isomers by delocalizing the single electron over a larger π system, resulting in a lower energy state for the intermediate. This concept is important in understanding the nature of bonds and how different substituents can affect the stability and reactivity of molecules.