C17: Aromatic Reactions Flashcards
sigma complex what is it
resonance stabilized carbocation, electrophile is joined to the benzene ring by new sigma bond
sigma complex is aromatic, anti-aromatic, nonaromatic
not aromatic because sp3
electrophilic substitution MECHANISM
[1] double bond attacks electrophile (+) and forms signma complex
[2] base abstracts H, which loses its electron to re-form double bond
How do you form an iodine cation?
1/2 I2 + H+ + HNO3 –> I+ +NO2 + H2O
Which is a stronger electrophile? what is needed to use the lesser?
I+, Br+
I+, FeBr3
cyclohexene + ____ —> 1,2 dibromocyclohexane
trans or cis?
Br2, trans
benzene + Br2 —->???
no reaction,
need lewis acid catalyst and will only get bromobenzene
benzene + Cl2 in what gives you chlorobenzene?
AlCl3
iodination of benzene is different from bromination and chlorination how?
iodination requires an acidic oxidizing agent (Nitric acid) not a catalyst
benzene + ____ in ______ —> nitrobenzene
HNO3, H2SO4
or hot Nitric acid (HNO3)
aromatic nitro groups (-NO2) are easily reduced to amino (-NH2) by ?????
Zn, Sn, or Fe in aqueous HCl
R-benzene + _____ —> R-benzene-NO2 —Zn, Sn, Fe, aq HCl—> ____?
[1] HNO3, H2SO4
[2] R-benzene-NH2
benzene + ___ in ____ —> benzenesulfonic acid
SO3 H2SO4
what is special about sulfonation?
it is reversible, with the addition of H20, H+ and heat
benzene –????—> benzene-d6
large excess of D2SO4/D2O
toluene structure
benzene with a methyl group
Methyl group of toluene is [1] because it is electron _____ and [2] and therefore
[1] an activating group, donating stabilizing the intermediate
[2] ortho, para-director
Toluene + +NO2 is favorable to what substitution? why?
ortho and para because positive charge is spread over two secondary carbons and one tertiary carbon
meta only spreads over three 2ndary carbons
energy state highest to lowest of nitration of benzene and toluene
benzene>meta>para,ortho
inductive stabilization direction, is it fast or slow
ortho, para-directing, faster tahn benzene
alkoxyl groups______ the rate of reaction because they ______
activate what positions?
increase, donate electrons to the pi bond (become + charged), ortho and para
anisole (benzene-O-CH3) + 3Br2 in H20 —-> ????
2,4,6-tribromoanisole + 3HBr
benezene-O-CH3 with Br at ortho and para positions
aniline (benzene-NH2) –???—> 2,4,6-tribromoanailine + _____
3Br2, H20, NaHCO3
activating ortho para directors groups
-O > -N(-R)R > -OH > -OR > -NH-C(=O)R > -R (no lone pairs)
activating ortho para directors benzene names
phenoxides > anilines > phenols > phenyl ethers > anilides > alkyl benzenes
nitrobenzene –HNO3, H2SO4, 100C–> ????
meta dinitrobenzene
electron donating are ____ of reactions
electron withdrawing are _____ of reactions
activators, deactivators
energy state highest to lowest of electrophilc addition to benzene and nitrobenzene
ortho,para>meta>benzene
deactivating groups are ______, ex:
electron withdrawing,
-NO2, -SO3H, -C(triplebond)N:, -C(=O)R [ketone or aldehyde], C(=O)-OR [ester], -N+R3 [quaternary ammonium]
halogenated benzene are _______ and ______directors
deactivating groups, ortho, para-directors
chlorobenzene + HNO3 in _____ —> ????
H2SO4, mostly para, ortho, not meta
energy state highest to lowest of electrophilc addition to benzene and chlorobenze
meta, ortho, para, benzene
activating groups are______ influential than deactivating groups
more
substituent strength -OH, -OR, -NR2 ___ -R, -X ____ -C=OR, -SO3H, -NO2
> , >, strongest to weakest
benzene + ___ in ___ –> benzene-R
R-X in lewis acid
X = Cl, Br, I
Lewis acid = AlCl3, FeBr3, etc
three steps of alkylation
1 form carbocation (R-X + Lewis Acid)
2 electrophilic attack by double bond on carbocation
3 loss of proton on ring by now -lewis acid reforms double bond in ring
alkenes + ____ —> carbocation
HF
alcohols + ____ —> carbocation
BF3
cyclopentanol + BF3 —> ???
cyclopentyl cation
Limitations to Friedel-Craft alkylation
1
2
3
1 order matters, activating group then deactivating group or change activating group into deactivating group 2 rearrangement (cannot add n-groups) 3 products are more reactive than starting material (over alkylation)
