16. Conjugated Systems

How many 𝝅 electrons are involved in the conjugated system for each of the following molecules?

(a)

Identify the isoprene units in the terpenes shown. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.

(a)

Phenolphthalein is an acid–base indicator that is colorless below pH 8 and red above pH 8. Explain briefly why the first structure is colorless and the second structure is colored.

Determine whether each structure is likely to be colored or not. For those that you predict to be colored, indicate the extended conjugation by marking the series of continuous sp² hybridized atoms.

(g)

Determine whether each structure is likely to be colored or not. For those that you predict to be colored, indicate the extended conjugation by marking the series of continuous sp² hybridized atoms.

(h)

Determine whether each structure is likely to be colored or not. For those that you predict to be colored, indicate the extended conjugation by marking the series of continuous sp² hybridized atoms.

(i)

a. How many MOs does 1,3,5,7-octatetraene have?

b. What is the designation of its HOMO (c1, c2, etc.)?

c. How many nodes does its highest energy MO have between the nuclei?

Why is this not a viable representation of the ψ₂, molecular orbital of buta-1,3-diene?

The ψ₂ molecular orbital for octa-1,3,5,7-tetraene is shown. Draw ψ₃.

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Hexa-1,3,5-triene uses six p orbitals, each containing a single electron, to make its three π bonds. How many total molecular orbitals are made by the six p orbitals?

Identify the isoprene units in the terpenes shown. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.

(b)

Identify the isoprene units in the terpenes shown. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.

(c)

Identify the isoprene units in the terpenes shown. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.

(e)

Vitamin E, especially the B ring and the side chain, is a terpenoid derivative. Identify the isoprene units nature used to make it.

For the following terpenes, identify the isoprene units. In cross-linked or ring-containing terpenes, linkages can be formed between more than just C₁ and C₄ of isoprene.

(a)