Question

Draw the products you would expect from conrotatory and disrotatory cyclizations of (2Z,4Z,6Z)-2,4,6-octatriene. Which of the two paths would you expect the thermal reaction to follow?

Short answer

The orientation of CH₃will depend on symmetry conservation. Whenever the mirror symmetry is observed there is called disrotatory mode which is rotation in opposite senses. Whereas in Conrotatory it’s just opposite the disrotatory case.

During the thermal reaction, only disrotatory will follow and the expected product will be cis form of the given molecule.

Step-by-step solution

The product expected from conrotatory and disrotatorycyclizations of a molecule given.

Con-rotation would give the opposite correspondence. The desired configuration will achieve during mechanism.

The thermal condition will followed in heat condition which is a case of dis-rotation and final product will be cis form of the given molecule

Whereas in photochemical condition (hv) is the case of con-rotation and final product as trans form of the given molecule.

This can be observed in the following figure:

They don’t follow con rotatory path due to 4n pi electrons in this case, also antiaromatic will be the transition state. Therefore this is not possible.

If we consider disrotatory mechanism then we can expect transition state as aromatic therefore this path way is most suitable and final product will be cis form of the molecule given.

The paths that can expected.

There are two paths that can be followed during thermal as well as photochemical conditions :

If we consider disrotatory mechanism then we can expect a transition state as aromatic therefore this pathway is most suitable and the final product will be a cis form of the molecule given.