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12.12
SubstituentEffectsinElectrophilic
AromaticSubstitution:
ActivatingSubstituents
Table12.2VerystronglyactivatingStronglyactivatingActivatingStandardofcomparisonisHDeactivatingStronglydeactivatingVerystronglydeactivatingClassificationofSubstituentsinElectrophilic
AromaticSubstitutionReactions
1.Allactivatingsubstituentsare
ortho-paradirectors.2.Halogensubstituentsareslightly
deactivatingbutortho-paradirecting.3.Stronglydeactivatingsubstituentsare
metadirectors.Generalizations
areortho-paradirectingandactivatingERGERGsinclude—R,—Ar,and—C=C
Electron-ReleasingGroups(ERGs)
areortho-paradirectingandstronglyactivatingERGERGssuchas—OH,and—ORare
stronglyactivatingElectron-ReleasingGroups(ERGs)
occursabout1000timesfasterthannitration
ofbenzeneOHHNO3OHNO2OHNO2+44%56%NitrationofPhenol
FeBr3catalystnotnecessaryOCH3Br2OCH3Br90%acetic
acidBrominationofAnisole
+HHHHHBrOCH3????HHHHHBr+OCH3????HHHHHBr+OCH3??OxygenLonePairStabilizesIntermediateallatoms
haveoctets
ERGswithalonepairontheatomdirectly
attachedtotheringareortho-paradirecting
andstronglyactivatingERGElectron-ReleasingGroups(ERGs)??
Alloftheseareortho-paradirecting
andstronglytoverystronglyactivatingExamplesERG=????OH??OR????OCR????O??NH2NHCR??O??NHR??NR2
LonePairStabilizesIntermediatesfor
orthoandparaSubstitutioncomparablestabilizationnotpossibleforintermediateleadingtometasubstitutionHHHHHX+ERGHHHHHX+ERG
12.13
SubstituentEffectsinElectrophilic
AromaticSubstitution:
StronglyDeactivatingSubstituents
ERGsStabilizeIntermediatesfor
orthoandparaSubstitutionHHHHHX+ERG??HHHHHX+ERG??
Electron-withdrawingGroups(EWGs)Destabilize
IntermediatesfororthoandparaSubstitutionHHHHHX+EWGHHHHHX+EWG —CF3isapowerfulEWG.Itisstronglydeactivatingandmetadirecting
AllofthesearemetadirectingandstronglydeactivatingManyEWGsHaveaCarbonylGroup
AttachedDirectl
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