浙江大学马成有机化学乙课件Chapter7 Conjugation in.docVIP

2009/9/131 Chapter 7: Conjugation in Alkadienes and Allylic Systems 2009/9/132 Summary A adjacent πsystemin the form of a double (or triple) bond can alter the characteristic chemistry of the functional group, due to the effects of resonance within a conjugated system This πsystem does not have to be all C as in a C=C or C≡C but can also contain heteroatoms, e.g. C=O or C≡N 1.Functional groups (independent units, conjugation units) 2.Allylic System 3.Dienes 4.Conjugation addition 5.Diels-Alder Reaction (M.O.) 2009/9/133 7.1 Conjugation 1.Some Dienes and Polyenes 2009/9/134 2.Conjugation In organic chemistry, Conjugation is used to describe: π ?π systems p- π systemsσ- π systems Character:Lowered Molecule Energy 1)The action not decreasewith the distance in the conjugation system 2)Charge changes one by one (electronegativety, electronic charge) Comared to inductive effect ! The fundamental ---Orbital involved in the bonding within the system 1)A continuous array of p orbitalsthat can align to produce a bonding overlapalong the whole system . (parallel and co-plane) 2)In σ- π systems,with σ orbitals, Pseudo-conjugation or Super- conjugation The Effect of three Conjugation: π – π p - π σ- π 2009/9/135 ?π – π CCCCCCC NCCC O H CCC CCC 2009/9/136 The native conformation of cyclooctatetraene. Adjacent double bonds are not coplanar, so there is not strong conjugation between them 2009/9/137 ? p – π ClCCRC O OH CH3CHCHCH2 2009/9/138 ? σ- π and σ-p OO CH2CHCH3 CC C HH H H H CH2CHC H H H CC H HH 2CC H H H CH2 H H CH3 CC H HH 2CC H H H H H CH2CH3 2009/9/139 ? The strength of conjugation Electronegativity and Major quantum number π – π (-C) 1) 2) CCCCCCC NCCCO CNR2CNR 2009/9/1310 ? p – π(+C) ?EN ?Major quantum number () NR2CCOHCCCCCCCCFCC 2009/9/1311 ?Diene a)Heat of Hydrogenation 2009/9/1312 ?Another stereoisomeric factor associated with conjugated dienes exist: Rotation about the single bond joining the two double bonds (colored blue)