Quiz - Delocalized π Systems and Dienes - 3 | Delocalized π Systems and Dienes

Organic Chemistry 2 - Quiz - Delocalized π Systems and Dienes - 3


Which statement is true concerning the allyl system in terms of molecular orbital theory?

The allyl system consists of two π bonds that allow the π electrons to be delocalized over three carbon atoms. Molecular orbital theory shows that this delocalization involves the formation of bonding (π) and antibonding (π*) molecular orbitals, with the electrons in a filled bonding orbital contributing to the stability of the system due to resonance.


Which statement best illustrates the concept of conjugation in a π system?

Conjugation refers to the overlap of p-orbitals across alternating single and double bonds, allowing for delocalization of π electrons. This results in increased stability, not decreased stability as mentioned in the third answer, and it does not require cyclic structures.


During the electrophilic addition to a conjugated diene, which factor primarily determines the regioselectivity of the addition?

The regioselectivity of electrophilic addition to a conjugated diene depends largely on the stability of the carbocation intermediates that form during the reaction. More stable intermediates will be favored, leading to the major product. Sterics and solvent polarity can influence the reaction but are generally secondary to carbocation stability.


Which of the following best describes the stabilization in a system with conjugated dienes?

Conjugated dienes are stabilized by the delocalization of π electrons across p orbitals that overlap through a single bond. This overlap allows for the resonance stabilization that is not present in isolated double bond systems or in chains that solely rely on hyperconjugation.


Which reaction is characteristic for an allylic position in a substrate?

The allylic position in a substrate is known for undergoing SN1 reactions due to the potential resonance stabilization of the carbocation intermediate. This stabilization leads to increased reactivity in SN1 reactions, in which the rate-determining step is the formation of the carbocation.


When comparing the reactivity of conjugated and isolated dienes to electrophiles, which of the following is correct?

Conjugated dienes are typically more reactive towards electrophiles than isolated dienes because the transition state during addition is lower in energy due to resonance stabilization. This makes the pathway for reaction more favorable energetically for conjugated dienes.


Considering the mechanism of the Diels-Alder reaction, which of the following describes the correct orientation of molecular orbitals?

The HOMO of the diene (highest occupied molecular orbital, a π orbital) interacts with the LUMO of the dienophile (lowest unoccupied molecular orbital, a π* orbital), leading to the formation of new σ bonds in the cyclohexene product.