Aromatic Hydrocarbons PPT Flashcards
is the generic term for an aromatic hydrocarbon
Arene
is derived by removal of a hydrogen
Aryl group
Aromatic compounds undergo what kind of reaction
Electrophilic Aromatic Substitution
draw the halogenation reaction and its reactants
grade yourself accordingly
draw the nitration reaction and its reactans
grade yourself accordingly
has a full or positive charge
electrophile
draw the sulfonation reaction and its needed reactants
Aromatic compounds undergo
draw the friedel crafts alkylation
grade yourself accordingly
draw the friedel crafts acylation
grade yourself accordingly
In step 1 of the mechanism, the electrophile reacts with two p electrons
from the aromatic ring to form a what
arenium ion
In step 2, a wha is removed and the aromatic system is regenerated
proton
generation of arenium ion is what kind of rxn
endothermic
The first step requires the loss of aromaticity of the very stable benzene ring, which is highly unfavorable
thus the first step is rate ____
determining
second step wherein the ring gains it aromatic substitution is highly
exothermic
which has a larger DG‡, first or second step
first step
The ring regains its aromatic stabilization, a highly favorable/unfavorable process
favorable
Halogenation of benzene requires the presence of a what
Lewis acid
A special apparatus is used to perform this reaction
fluorination
occurs so rapidly it is hard to stop at
monofluorination of the ring
fluorination
is so unreactive that an alternative method must be used
iodine
draw the iodination reaction
grade yourself accordingly
in nitration, the nitric acid can dissociate to form a what
nitronium ion
is the actual electrophile in nitration; it reacts with benzene to form a resonance-stabilized arenium ion
nitronium ion
Sulfonation occurs most rapidly using what
fuming sulfuric acid
fuming sulfuric acid is made out of
conc. sulfuric acid that contains SO3
is an equilibrium reaction; all steps are equilibria
sulfonation
The sulfonation product is favored by use of what kind of H2SO4
concentrated or fuming
can be accomplished using dilute sulfuric acid
desulfonation
sulfuric acid with a high concentration of water
dilute sulfuric accid
another way for desulfonation aside from using dillute sulfuric acid
passing steam through the reaction and collecting the volatile desulfonated compound as it distils with the steam
in the friedel-crafts alkylation what does the Lewis acid do
generate a carbocation electrophile
Friedel-Crafts Alkylation is named after
Charles Friedel
James M. Crafts
probably do not form discreet carbocations but
the primary carbon in the complex develops considerable positive charge
primary alkyl halides
carbonyl attached to some R group
acyl group
requires reaction of an acid chloride or acid anhydride with a Lewis acid such as aluminium chloride
Friedel-Crafts Acylation
acid chlorides are made from what
carboxylic acids
The electrophile in Friedel-Crafts acylation is an
acylium ion
also make the ring less reactive to Friedel-Crafts
reaction because they become electron-withdrawing groups upon Lewis acid-base reaction with the Lewis acid catalyst
amino groups
give groups that usually give poor yields in Friedel Crafts reaction
grade yourself accordingly
cannot be used in Friedel-Crafts reactions because they do not form carbocations readily
aryl and vinyl halides
occurs frequently with Friedel-Crafts alkylation because the first alkyl group introduced activates the ring toward further substitution
polyalkylation
does not occur because the acyl group deactivates the aromatic ring to further substitution
polyacylation
synthetic application of friedel-crafts acylation
Clemmensen reduction
Clemmensen reduction reduces C=O to
methylene group
Clemmensen reduction reduces C=O to
methylene group
conditions of Clemmensen reduction
Zn(Hg) / HCl
more reactive than benzene
activating groups
less reactive than benzene
deactivating groups
direct future substitution to the o- and p- positions
o/p-directors
directors direct future substitution to the m position
m directors
all activating groups are what
o/p-directors
The halides are also ortho-para directors but are
mildly deactivating
Strong electron-withdrawing groups such as
nitro
carboxyl
sulfonate
deactivating o/p directors include
Cl and Br
activate the ring toward further reaction
electron donating groups
stabilize the transition state of the first step
of substitution and lead to lower DG‡ and faster rates of reaction
electron-donating groups
deactivate the ring toward further reaction
electron withdrawing groups
destabilize the transition state and lead
to higher DG‡ and slower rates of reaction
electron-withdrawing groups
most electron donating compounds include
-NH2
-NR2
-OH
-OR
meta directing groups have wha charge
partial or positive charge
what does o/p directors contribute
fourth important resonance form
