Question

In the sigmatropic rearrangement shown below, which of the following choices explains the difference in products for thermal and photochemical conditions?

• A. The photochemical product is too strained to form unless an electron in the starting material is promoted to a higher energy orbital.
• B. The photochemical product only forms when irradiated with light because the product is higher energy than the starting material.
• C. The photochemical product only forms when irradiated with light because the thermal product is identical to its starting material.
• D. Orbital symmetry arguments allow for the $1,3$-rearrangement to occur only from the photochemical HOMO and a $1,5$-rearrangement to occur only from the original (thermal) HOMO.

Answer 1

The correct option is B The photochemical product only forms when irradiated with light because the product is higher energy than the starting material.

The method of ring closure of a photochemical electrolytic reaction is opposite to that of a thermal electrocyclic reaction for the same number of $\pi$ bonds.

answer is (B)