In the UV-vis. Spectrum of benzene, the absorption that corresponds to the HOMO-LUMO transition occurs at 184 nm . How does this compare to the corresponding electron transition in hexa-1, 3, 5-triene and the significant difference is to be explained. Concept introduction: In UV–vis. spectroscopy, absorption of a photon promotes an electron from a lower energy MO to a higher-energy MO. λ max for the longest-wavelength (lowest-energy) absorption in the spectrum generally corresponds to the HOMO–LUMO transition. In a π → π* transition, an electron from a π MO is promoted to a π* MO. In an n → π* transition, an electron from a nonbonding MO is promoted to a π* MO. Conjugation decreases the energy difference between the HOMO and LUMO, and thus increases the wavelength of the photons absorbed.

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Chapter 15, Problem 15.38P

Interpretation Introduction

Interpretation:

In the UV-vis. Spectrum of benzene, the absorption that corresponds to the HOMO-LUMO transition occurs at 184 nm. How does this compare to the corresponding electron transition in hexa-1, 3, 5-triene and the significant difference is to be explained.

Concept introduction:

In UV–vis. spectroscopy, absorption of a photon promotes an electron from a lower energy MO to a higher-energy MO. λmax for the longest-wavelength (lowest-energy) absorption in the spectrum generally corresponds to the HOMO–LUMO transition. In a π→π* transition, an electron from a π MO is promoted to a π* MO. In an n→π* transition, an electron from a nonbonding MO is promoted to a π* MO. Conjugation decreases the energy difference between the HOMO and LUMO, and thus increases the wavelength of the photons absorbed.

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