orgo addition reactions of conjugated dienes

chapter 10

conjugated system

one that consists of more than two adjacent atoms that have p orbitals that overlap sideways (parallel unhybridized p orbitals on sp2 or sp hybridized)

when 3 or more adjacent atoms have parallel unhybridized p orbitals

system is conjugated, interactions are pi interactions

conjugated dienes

cumulative, isolated, conjugated dienes

cumulative dienes

double bonds share sp2 and sp hybridized carbons some are chiral

isolated dienes

at least two or more single bonds between the two double bonds

conjugated dienes

double bond separated by a single bond

conjugated dienes have

conformational and stereoisomers

two possible conformers result from

rotation around cc bond that join the two double bonds

s trans conformation is

2.3 kcal lower in energy than s cis conformation because of steric repulsion of hydrogen

s trans is more stable but s cis

play important role in some diene reactions

conjugated dienes are more stable than non conjugated dienes bc

delocalization of electrons from resonance

high heat of hydrogenation means less

stable

difference in heat of hydrogenation is measure of

resonance energy

homo

highest occupied molecular orbital

lumo

lowest occupied molecular orbital

allyl conjugated intermediate

3 adjacent carbons conjucatedv

valence bond approach

draw contributing structures with resonacne