16. Conjugated Systems

Which of the following molecular orbitals would you use to model a thermal electrocyclization reaction using frontier orbital theory?

Given the following molecular orbital diagram for diatomic molecules, which of the following species is expected to be the most stable? (Assume the diagram is for second-period homonuclear diatomics and consider bond order only.)

According to molecular orbital theory, which of the following correctly represents the order of molecular orbitals for $N_2$ from lowest to highest energy?

According to molecular orbital theory, what is the highest occupied molecular orbital (HOMO) for the molecule $B_2$?

According to molecular orbital theory, the thermal electrocyclic ring closure of ${\mathrm{1,3}}_{\text{butadiene}}$ to cyclobutene proceeds via which type of orbital motion?

What is another name for the molecular orbital theory of bonding in metals?

Which of the following statements is true for $\mathrm{molecular} \mathrm{orbitals}$?

Which of the following best describes the molecular orbital (MO) electron diagram for the $O^2+$ molecular ion?

Which of the following best describes the steps to construct a molecular orbital interaction diagram for $O_2$?

Below is one of the molecular orbitals of $HF$. Which of the following best describes the orbital?

Why are conjugated molecules like the product of the ninhydrin reaction brightly colored?

(a) Draw the molecular orbitals for the cyclopropenyl case.

(Because there are three p orbitals, there must be three MOs: one all-bonding MO and one degenerate pair of MOs.)

(b) Draw an energy diagram for the cyclopropenyl MOs. (The polygon rule is helpful.) Label each MO as bonding, nonbonding, or antibonding, and add the nonbonding line. Notice that it goes through the approximate average of the MOs.

(c) Add electrons to your energy diagram to show the configuration of the cyclopropenyl cation and the cyclopropenyl anion. Which is aromatic and which is antiaromatic?