[davidenarb]

Hi all

In the bellow transformations, we have a pathway to change the configuration form one double bond from E to Z.
the first transformation is carried out through thermal conditions, and since we have an odd number (3) of double bonds, so we have a disrotatory temporary ring.

I didn't understand, however, the second transformation because it goes from an even number of double bonds (2) under photochemical conditions, and the outcome is a conrotatory product. In the Woodward-Hoffmann rules, the type of rotation in photochemical conditions and an even number of double bonds is disrotatory not conrotatory.

I have one more question concerning the second transformation: I have troubles to imagine how can we have the Z configuration of the product. it is difficult for me to imagine the conrotatory fashion applied in the second transformation so that the product will be formed with the geometry of a Z configuration of one double bond. Please how can I enhance my understanding so that I will be able to see the geometry of the second transformation.

Thank you

[davidenarb]

I didn't understand, however, the second transformation because it goes from an even number of double bonds (2) under photochemical conditions, and the outcome is a conrotatory product. In the Woodward-Hoffmann rules, the type of rotation in photochemical conditions and an even number of double bonds is disrotatory not conrotatory.

The first part of my question is understood. The reason of having a conrotatory rotation of the outermost lobes is because it is a ring opening and not ring closure transformation.

The second part of my question remains moot.

[orgopete]

If I understand your second question correctly, then I suggest models. I believe you will be able to see the two configurations can be satisfied within the ring.

[davidenarb]

If I understand your second question correctly, then I suggest models. I believe you will be able to see the two configurations can be satisfied within the ring.

This is what I actually tried to do, but when I open the ring, I feel puzzled to picture the Z configuration of one of the double bond. Is there any other tip please?