Question

If isomer A is heated to about 100 °C, a mixture of isomers A and B is formed. Explain why there is no trace of isomer C or D.

Short answer

Under thermal conditions, the conrotatory product is major.

Step-by-step solution

Clockwise ring-closing

The ring closes under the clockwise thermal condition and gives a conrotatory product.

Counter clockwise ring-closing

The counter-clockwise direction gives isomer B, not isomer C and D.