16. Conjugated Systems

Consider the MO's of allyl anion. Which of the following are HOMO and LUMO?

Identify the HOMO and LUMO of the allylic cation and the allylic anion shown in Figure 21.22.

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Draw the molecular orbital picture for (a) ethene. Label the HOMO and LUMO of each.

Predict the λ_max of the following compound:

Match four of the following UV absorption maxima (λ_max) with the corresponding compounds: (1) 232 nm; (2) 256 nm; (3) 273 nm; (4) 292 nm; (5) 313 nm; (6) 353 nm.

How can you use UV spectroscopy to distinguish between the compounds in each of the following pairs?

a.

Rank the following compounds in order of increasing lmax:

Rank each set of compounds in order of decreasing λ_max:

b.

Rank each set of compounds in order of decreasing λ_max:

a.

Which of the following are correct? Correct any false statements

c. A conjugated diene with an odd number of double bonds has a symmetric HOMO.

Draw the molecular orbital picture of octa-1,3,5,7-­tetraene, indicating which is the HOMO and which is the LUMO.

Which of the following molecules would you expect to absorb in the visible region of the electromagnetic spectrum?

(e)

Would you expect the following molecules to absorb in the UV–visible region of the electromagnetic spectrum?

(a)

(b)

(c)

(d)

(e)