Which of the following is the most likely to happen when a conjugated diene is irradiated with ultraviolet light?
A)The bonds between different atoms in the molecule undergo symmetric stretching.
B)A electron is promoted from the highest occupied molecular orbital to the lowest unoccupied molecular orbital.
C)A electron is demoted from the lowest occupied molecular orbital to the highest unoccupied molecular orbital.
D)The bonds between different atoms in the molecule undergo asymmetric stretching.

Question

​Which of the following is the most likely to happen when a conjugated diene is irradiated with ultraviolet light?
A)​The bonds between different atoms in the molecule undergo symmetric stretching. 
B)​A electron is promoted from the highest occupied molecular orbital to the lowest unoccupied molecular orbital. 
C)​A electron is demoted from the lowest occupied molecular orbital to the highest unoccupied molecular orbital. 
D)​The bonds between different atoms in the molecule undergo asymmetric stretching.

Quizplus · Accepted Answer

When a conjugated diene is irradiated with ultraviolet light, a photon is absorbed, which can promote an electron from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). This causes a change in the electronic configuration of the molecule and can lead to the formation of new chemical species. Symmetric and asymmetric stretching of bonds in the molecule may occur as a result of these changes, but the promotion of an electron is the most likely initial event. Therefore, choice B is the best answer.

​Which of the Following Is the Most Likely to Happen

Which of the Following Is the Most Likely to Happen