benzene
styrene
(C6H5)CH=CH2
friedel crafts
(benzene ring with R group) make R group add to benzene ring with AlCl3 catalyst
Substituents affects two aspects of Electrophilic aromatic substitution:
1) The rate of the reaction: can react faster of slower than benzene. 2)The orientation: New group located either ortho, para, or meta to the existing substituent. The identity of the first substituent determines the position of the second substituent.
3 facts about Friedel Crafts Alkylation
1) Vinyl halides and aryl halides do not react in Friedel-Crafts alkylation. (the carbocations that could be for from these species are too unstable. 2) Rearrangements can occur in order to form a more stable carbocation electrophile. 3) Other functional groups that form carbocations can also be used as starting materials. Ex. Alkenes, alcohols are common and used in the presence of a strong acid.
ortho
1,2 positions
meta
1,3 positions
para
1,4 positions
Electrophilic aromatic substitution reactions
1. Halogenation (Br/FeBr3, Cl/FeCl3, or I/HNO3) 2. Nitration (NO3/ H2SO4) 3. Sulfonation (H2SO4) 4. Friedel-Craft acylation (Acyl chlorides with AlCl3) 5. Friedel-Craft alkylation(alkyl chlorides and AlCl3, possible rearrangement)
Aromatic Compounds
1. a compound must have an uninterrupted cyclic cloud of x electrons above and below the plane of the molecule. And they are unusually stable 2. the x cloud must contain an odd number of pairs and x electrons.
TNT
2,4,6-trinitrotoluene, the 3 nitro groups give explosive properties
-NO2, -SO2, -CN
3 possible deactivating groups
triol
3OH
-OH2, -NH2, -OR, -NR2, alkyl
5 possible activating groups
monosubstituted
A benzene with one additional group is....
disubstituted
A benzene with two additional groups is...
aromatic compound
A cyclic hydrocarbon with delocalised pi electrons
hydroxyl group
A functional group consisting of a hydrogen atom joined to an oxygen atom by a polar covalent bond. Molecules possessing this group are soluble in water and are called alcohols.
3
A meta substituent of a benzene is in position ___ relative to the primary substituent
4
A para substituent of a benzene is in position ___ relative to the primary substituent
ortho
A substituent of a disubstituted benzene that is next to the primary substituent
para
A substituent of a disubstituted benzene that is three down from the primary substituent
meta
A substituent of a disubstituted benzene that is two down from the primary substituent
deactivating group, meta director
A substituent of an aromatic compound that slows down electrophilic substitution
activating group, O-P director
A substituent of an aromatic compound that speeds up electrophilic substitution
benzyl
A toluene as a substituent without a hydrogen on its methyl group is called a ____ group
RCOCL/AlCl₃
Acylation Benzene ring is treated with an acid chloride. The transfer of an acyl group from one atom to another.
RCl/AlCl₃
Alkylation The transfer of an alkyl group from one atom to another (from Cl to Benzene)
Br+
An example of a powerful electrophile
2
An ortho substituent of a benzene is in position ___ relative to the primary substituent
Relative stability
Aromatic compound > cyclic compound with localized electrons> anti-aromatic compound
phenyl, aryl
As a substituent, an aromatic ring is called either a ___ or a ___ group
phenol
Benzene ring with an OH group directly attached to it
xylene
Benzene with two methyl groups in ortho, para, or meta positions
ether
C-O-C, a compound containing an oxygen bonded to 2 carbon atoms
phenyl group
C6H5-, Benzene ring attached to a parent compound
benzene
C6H6, leukemia
arene
Compound derived from benzene
All activators are?
Either R groups or have an O or N atom bonded to a lone pair bonded directly to the benzene ring.
Anti-aromatic Compounds
Even number of x electron pairs
X₂/FeX₂ X=Cl₂ or Br₂
Halogenation
electrophile
In electrophilic aromatic substitution, this replaces a hydrogen in the original molecule
M
In the presence of a deactivating group, the electrophile is most likely to be added at this position
O, P
In the presence of an activating group, the electrophile is most likely to be added at this position
positive charge stabilised by resonance
Intermediate step in an electrophilic substitution reaction
HNO₃/H₂SO₄
Nitration
anisole
OCH3 attached to a benzene ring
KMnO₄
Oxidation
Substituent causes electron donating in benzene
Polarizable alkyl groups donate electron density, and thus exhibit an electron-donating inductive effect.
Nitrobenzene
Reacts more slowly than benzene in all substitution reactions. Electron withdrawing NO₂ group deactivates the benzene ring to electrophilic attack. NO₂ is a meta director.
H₂, Pt/2000 psi
Reduction of Ring and Substituent to Single Bonds
H₂/Pd
Reduction of Substituent to Single Bonds
Zn(Hg), HCl or NH₂ NH₂ + OH-
Reduction to Alkyl
Pd/H₂ or Fe/HCL or Sn/ HCL
Reduction to Aniline
Ortho, Para directors and activators
Substituents that activate (make more reactive) a benzene ring and direct substitution ortho and para. Ex. -R or -Z:
Ortho, Para Deactivators
Substituents that deactivate (less reactive) a benzene ring and direct substitution ortho and para. Ex. All halogens.
nitration
Substitution of a nitro group (-NO2) for one of the ring H. The reaction occurs when benzene reacts with nitric acid in the presence of sulfuric acid as catalyst
SO₃/H₂SO₄
Sulfonation
Electron withdrawing groups destabilizes?
The Carbocation and deactivate a benzene ring towards electrophilic attack.
Electron donating groups stabilize?
The carbocation and activate a benzene ring towards electrophilic attack.
stable
The delocalised pi electrons in an aromatic compound mean it is very...
effect of a Halogen directly bonded to a benzene ring
The inductive effect dominates and the net effect is electron withdrawal.
electrophilic aromatic substitution
The most important reaction of aromatic rings
powerful
The property the electrophile must have to participate in electrophilic aromatic substitution
Neutral O or N atom bonded directly to benzene
The resonance effect dominates and the net effect is electron donation.
benzene
The simplest aromatic compound
cyclic, delocalised pi electrons
The two defining features of an aromatic compound
Resonance effect "electron donating"
When resonance structures place a negative charge on carbons of the benzene ring. * observed whenever an atom Z having a lone pair of electrons is directly bonded to a benzene ring.
Resonance effect "electron withdrawing"
When resonance structures place a positive charge on carbons of the benzene ring. *observed in substituted benzenes having the general structure C₆H₅-Y=Z where z is more electronegative than Y.
phenyl substituent
a benzene ring is a substituent, it is called a phenyl group
toluene
a benzene ring w/ a methyl group ** reacts faster than benzene in all substitution reactions.
benzyl substituent
a benzene ring with a methylene group is called a benzyl group. -CH2-
simmons smith
a carbenoid reacts with a alkene to form a cyclopropane
mercaptans
a common name for any molecule containing an -SH group
All meta directors have
a full partial positive charge on the atom bonded to the benzene ring.
aryl group
a group derived from an arene by removal of an H atom from an arene and given the symbol Ar-
steric effects
a group influences another group by filling space
polynuclear aromatic hydrocarbon
a hydrocarbon containing two or more benzene rings, each of which shares two carbon atoms with another benzene ring
pyridine
a ring with a non carbon atom
zwitter ion
an ion with both + and - charges in same ion
deuterium
an isotope of hydrogen which has one neutron (as opposed to zero neutrons in hydrogen)
diol
any of a class of alcohols having 2 hydroxyl groups in each molecule
All ortho and paradirectors
are R groups or have a non bonded electron pair on the atom bonded to the benzene ring.
Kahn Ingold Prelog rules
are a set of rules used in organic chemistry to name the stereoisomers of a molecule. assign an R or S descriptor to each stereocenter and an E or Z descriptor to each double bond
benzoic acid
benzene with a -O= -OH group
benzonitrile
benzene with a 3 (-) N
Toluene
benzene with a CH3 group Ch3 group is an ortho, para director.
Anisole
benzene with a CH3O group
styrene
benzene with a CH=CH2 group
Aniline
benzene with a NH2 group
benzenesulfonic acid
benzene with a SO3H group
benzaldehyde
benzene with a aldehyde mark
Phenol
benzene with an OH group
Resonance effects of substituent on benzene ring
can either donate or withdraw electron density, depending on whether they place a positive or negative charge on the benzene ring.
geminal carbon
carbon attached to same parent carbon
electrophilic aromatic substitution
chemistry of benzene rings
aromatic sextet
closed loop of electrons (two from the second bond of each double bond) characteristic of a benzene ring
wurtz reaction
coupling of C atoms to make alkane (couple free radicals)
All deactivators are?
either halogens or they have an atom with a partial or full positive charge bonded directly to the benzene ring. These are electron withdrawing groups.
hoffman product
formed by reaction with a big bulky base. Potassium T Butoxide
initiator
free radical that starts polymerization
alcohols
functional group, OH bonded to tetrahedral carbon atom
exocyclic
hoffman product
Substituent causes electron withdrawing in benzene
more electronegative atoms than carbon pull electron density away from carbon and thus exhibit an electron-withdrawing inductive effect.
thiols
organic compounds containing sulfhydryls (-SH) group bonded to a tetrahedral carbon
Lindlar reaction
reduces triple bonds to double bonds using a heterogenous catalyst. This stops a reaction
carbene
sp2 hybridized carbon atom, has a lone pair
Meta directors
substituents that direct substitution meta. all meta directors deactivate the ring. Ex. -Y(delta + or minus) order in increasing deactivation: -CHO, -COR,-COOR, -COOH, -CN, -SO₂H, -NO₂, N⁺R₃
dehydration
the elimination of a molecule of water from an alcohol. OH is removed from one carbon and H is removed from the other
hydrogen bonding
the intermolecular force in which a hydrogen atom that is bonded to a highly electronegative atom is attracted to an unshared pair of electrons of an electronegative atom in a nearby molecule
endocyclic
zaietz's rule
