Lecture 17 - Alkynes; Conjugation in Allylic Intermediates and Dienes. Because of their unusual acidity very strong base makes it possible to isomerize an internal acetylene to the less stable terminal isomer.
Many chemical reactions may be understood in terms of localized bonds, but the special stability of conjugated systems requires considering delocalized orbitals or "resonance." Equilibrium constants, rates, and regiochemistry
in systems involving allylic cations, anions, transition states, and free radicals demonstrate that allylic conjugation is worth about 13 kcal/mole. Regioselection in addition of DCl to 1,3-pentadiene reveals rapid collapse of
an allylic ion pair. Allylic substitution of bromine can be favored over Br2 addition by using NBS to control Br2 concentration. Diene conjugation is worth much less than allylic conjugation.
(from oyc.yale.edu)
Lecture 17 - Alkynes; Conjugation in Allylic Intermediates and Dienes
Time
Lecture Chapters
[00:00:00]
1. Addition to Acetylenes: Regio- and Stereochemistry
[00:14:07]
2. Acidity and Isomerization of Acetylenes
[00:20:32]
3. When Does Conjugation Matter? Allylic Intermediates and Transition States