Lecture09outline

Lecture09outline - I. Review A ranking of common donor...

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I. Review • A ranking of common donor groups: -NR 2 > -NHC(O)R ~ -OR > -OC(O)R ~ -R > -H > halide • The donor effects only occur if the lone pair is properly aligned with the p-orbitals of the ring • Donation of the lone pair of these groups into the ring makes the substituents less basic and nucleophilic • Electron withdrawing groups all have a structure in which the aromatic ring is bonded to a π -bond that contains an electronegative atom at the distal position • Common electron withdrawing groups include –NO 2 , -C(O)X, -SO 3 H, -CN • Resonance models show that these groups pull electron density from the aromatic ring selectively at the ortho and para positions • This results in slow electrophilic aromatic substitution, but the meta positions react less slowly than the ortho and para positions • This pattern leads to electron withdrawing groups being called meta-directing • Nitro groups cannot be converted directly to diazonium ions, but they can be converted to amines with H
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Lecture09outline - I. Review A ranking of common donor...

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