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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