Solomons & Fryhle: Organic Chemistry 8th Ed., Wiley 2004

Organic chemistry IZdeněk Friedl

Chapter 7

Alkadienes

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Alkadienes

• structure of alkadienes• stability of alkadienes• reaction scheme of alkadienes• regioselectivity of addition AE reactions• kinetic vs. thermodynamic controlled reactions• Diels-Alder reactions• regiospecifity of Diels-Alder reactions• endo vs. exo products of Diels-Alder reactions

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The π-electron structure of 1,2 , 1,3 and 1,4-alkadienescumulated, conjugated, isolated dienes

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The π- orbital structure of 1,3-butadieneconjugation of π-orbitals a lower energy

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Heats of hydrogenation of alkenes and alkadienes I

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Heats of hydrogenation of alkenes and alkadienes IIheats of hydrogenation of 2 moles of 1-butene and 1 mole of 1,3-butadiene

TheThe differencedifference ofof 15 kJ mol15 kJ mol--11 aa conjugationconjugation energyenergy

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The reaction scheme of alkadienes

R CH = CH CH2 CH = CH2

AR

AE

AE (1,2- / 1,4- )1234

==

CH = CH2 CH = CH R

cycloaddition

(AR)

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AE Regioselectivity of addition reactionson conjugated 1,3-alkadienes

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AE Kinetic vs. thermodynamic controlled reactions1,2- and 1,4-addition reactions

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AE Kinetic vs. thermodynamic controlled reactions

An importance of ∆G‡ vs. ∆G° energies

∆G‡1,4 > ∆G‡

1,2

∆G°1,2 > ∆G°1,4

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Diels-Alder reactions(4+2)π 1,4-cycloaddition reactions

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Stereospecifity of Diels-Alder reactions

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Endo vs. Exo products of Diels-Alder reactions