16. Conjugated Systems

What does it mean for a molecule or intermediate to be conjugated?

Which of the following molecules is conjugated?

a. How many linear dienes have molecular formula C6H10? (Disregard cis–trans isomers.) b. How many of the linear dienes in part a are conjugated dienes?

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene: g. How many nodes does the highest-energy MO of 1,3,5,7-octatetraene have between the nuclei?

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene: e. Which MO is the HOMO and which is the LUMO in the excited state?

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene: d. Which MO is the HOMO and which is the LUMO in the ground state?

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene: c. Which MOs are symmetric, and which are antisymmetric?

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene: a. How many MOs does the compound have?

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. (b) farnesol

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. (c) menthol

(••••) North American termite soldiers, when encountering enemy insects, contract their mandibular muscles, expelling a mixture of chemicals that essentially trap their enemies in a glue-like substance. This weapon, built into the face of the termite, is called the fontanellar gun. It releases a mixture of pinene (62%), myrcene (27%), and limonene (11%). pinene myrcene limonene 62% 27% 11% (a) Identify the isoprene units in pinene, myrcene, and limonene.

Answer the following questions for the molecular orbitals (MOs) of 1,3,5,7-octatetraene: f. What is the relationship between HOMO and LUMO and symmetric and antisymmetric orbitals?

Write the appropriate reagent over each arrow.

b. Can a high-resolution mass spectrometer distinguish between them?

(•••) Suggest the appropriate reagents to carry out the following transformations. (b)

(•••) Suggest the appropriate reagents to carry out the following transformations. (c)

Classify the following dienes and polyenes as isolated, conjugated, cumulated, or some combination of these classifications. (a) cycloocta-1,4-diene (b) cycloocta-1,3-diene (c) cyclodeca-1,2-diene (d) cycloocta-1,3,5,7-tetraene (e) cyclohexa-1,3,5-triene (benzene) (f) penta-1,2,4-triene

(•) How many 𝝅 electrons are involved in the conjugated system for each of the following molecules? a.

Classify the following conjugated systems as having 4n or 4n + 2 π electrons. (c)

Classify the following conjugated systems as having 4n or 4n + 2 π electrons. (f)

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)