Chapter 16
Dienes, Conjugated Pi Systems, and Pericyclic Reactions
![Structure of Conjugated Dienes](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/12406.jpg)
Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like…
![Stability of Conjugated Dienes](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/12544.jpg)
Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering…
![π Molecular Orbitals of the Allyl Cation and Anion](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/12408.jpg)
An allyl group is a three-carbon conjugated system where the sp³-hybridized allylic carbon is bonded to a CH=CH2 group via a single bond.…
![π Molecular Orbitals of the Allyl Radical](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/13090.jpg)
Allyl radicals are three-carbon conjugated systems. They are readily formed as intermediates in halogenation reactions of alkenes involving the…
![Electrophilic 1,2- and 1,4-Addition of X<sub>2</sub> to 1,3-Butadiene](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/13091.jpg)
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.
Conjugated dienes…
![Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/12410.jpg)
The addition of a hydrogen halide to 1,3-butadiene gives a mixture of 1,2- and 1,4-adducts. Since more substituted alkenes are more stable, the…
![UV–Vis Spectroscopy: Woodward–Fieser Rules](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/13027.jpg)
UV–Visible absorption spectra of conjugated dienes arise from the lowest energy π → π* transitions.…
![Pericyclic Reactions: Introduction](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/13092.jpg)
Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through…
![Thermal Electrocyclic Reactions: Stereochemistry](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/12413.jpg)
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the…
![Photochemical Electrocyclic Reactions: Stereochemistry](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/12414.jpg)
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state.…
![Cycloaddition Reactions: MO Requirements for Thermal Activation](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/13093.jpg)
Thermal cycloadditions are reactions where the source of activation energy needed to initiate the reaction is provided in the form of heat. A typical…
![Cycloaddition Reactions: MO Requirements for Photochemical Activation](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/13094.jpg)
Some cycloaddition reactions are activated by heat, while others are initiated by light. For example, a [2 + 2] cycloaddition between two ethylene…
![Diels–Alder vs Retro-Diels–Alder Reaction: Thermodynamic Factors](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/12418.jpg)
The Diels–Alder reaction is thermally reversible, meaning that the reaction reverts to the starting diene and dienophile under suitable…
![Diels–Alder Reaction Forming Cyclic Products: Stereochemistry](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/12419.jpg)
The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic…
![Diels–Alder Reaction: Characteristics of Dienes](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/12420.jpg)
The Diels–Alder reaction brings together a diene and a dienophile to form a six-membered ring. Both components have unique characteristics that…
![Diels–Alder Reaction: Characteristics of Dienophiles](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/13096.jpg)
In a Diels–Alder reaction, the diene is usually an electron-rich system and acts as a nucleophile, whereas the dienophile is electron-deficient…
![[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/12422.jpg)
The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves…
![[3,3] Sigmatropic Rearrangement of Allyl Vinyl Ethers: Claisen Rearrangement](https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/13097.jpg)
The Claisen rearrangement is a [3,3] sigmatropic rearrangement of allyl vinyl ethers to unsaturated carbonyl compounds. The rearrangement is a…
![Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes](https://cloudfront.jove.com/files/thumbs/50511_t.png)
Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules…
![Facile Preparation of (2<em>Z</em>,4<em>E</em>)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate](https://cloudfront.jove.com/files/thumbs/55766_t.png)
Direct cross-coupling between two alkenes via vinylic C-H bond activation represents an efficient strategy for the synthesis of butadienes with high…