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CHM 303: CHAPTER 12 - REACTIONS OF ARENES
what does EAS stand for
|
electrophilic aromatic substitutions
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EAS general format
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Ar-H + E-Y ---> Ar-E + H-Y
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mechanisms of general EAS
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E+ addition to π-bond, H+ transfer/ rearomatization
|
types of special EAS rxns
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halogenations, nitration, sulfonation, alkylation, acylation
|
Friedel-Crafts Rxns
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alkylations, acylations
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what is the favored catalyst in EAS halogenations
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iron (FeBr3, FeCl3)
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what reagents are needed in EAS halogenations?
|
Br2, FeBr3
Cl2, FeCl3
|
what reagents are needed in EAS nitrations?
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HNO3, H2SO4
acidic environment
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what E+ gets created for EAS halogenations
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X-X+--FeBr3
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what E+ gets created for EAS nitrations
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O=N+=O nitronium ion
|
what reagents are needed for alkylations
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AlCl3, R-Cl
-or-
alkene, acid
|
in alkylations, what type of E+ is created
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carbocation
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what must we be aware of in alkylations
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rearrangements via hydride shift
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what reagents are needed for acylations
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AlCl3, R-C-Cl
//
O
|
acylations are (more/less) reliable than alkylations - why
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more - no carbocation rearrangement problems
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two types of acylations reductions
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Clemmensen reduction, Wolff-Kishner reduction
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Clemmensen reductions are done in what type of environment?
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acidic
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Wolff-Kishner reductions are done in what type of environment?
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basic
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what are the two factors of substituent effects?
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rxn rate, regeoselectivity
|
what are ring activators
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electron donating groups that speed up reactions
|
what are ring deactivators
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electron withdrawing group that slows down rxn
|
what are the two types of directors
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ortho/para directing, meta directing
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activators (add/withdraw) electron density
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add to ring
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deactivators (add/withdraw) electron density
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withdraw from ring
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activating groups (increase/decrease) E+ attackability
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increase
|
deactivating groups (increase/decrease) E+ attackability
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decrease |
examples of activating groups
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atoms with lone pairs attached to ring, alkyl groups
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examples of deactivating groups
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carbonyl groups, nitro groups, nitriles, halogens
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where is electron density the greatest and lowest with activating groups?
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greatest: ortho and para carbons
lowest: meta carbons
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where is electron density the greatest and lowest with deactivating groups?
|
greatest: meta carbons
lowest: ortho and para carbons
|
all meta-directors are ring (activators/deactivators)
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deactivators
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all ortho/para-directors are ring (activators/deactivators) except ____
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activators except halogens
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-R is what type of director
|
ortho/para
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-OH, -OR are what type of directors
|
ortho/para
|
-NH2, -NHR, -NR2 are what type of directors
|
ortho/para
|
-O-C-R, -NH-C-R are what type of
// // directors
O O
|
ortho/para
|
halogens are what type of director
|
ortho/para
|
-NO2, -SO3H are what type of directors
|
meta
|
-C≡N, -CF3 are what type of directors
|
meta |
-C-H, -C-R are what type of directors
// //
O O
|
meta |
-C-OH, -C-OR, -C-NR, -C-X are what
// // // // type of
O O O O directors
|
meta |
ortho/para directors: atom attached to ring has what
|
lone pair electrons
|
meta directors: atom attached to ring has what
|
positive charge
|
with multiple substituent the effects are ______
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cummulative
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which substituent controls regeoselectivity when there are multiple substituents
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more strongly activating group
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what must one consider regarding regeoselectivity and multiple substituents
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steric hinderance
|