Organic chemistry chapter 17

Electrophilic substitution must happen in a _____ medium for aromatic rings.

basic

Why does FeBr3 allow for bromination of the usually non-reactive benzene?
the Br2 attaches to it and makes a strong nucleophile, attacking the carbon with the first bromine, then attacking the hydrogen with the second to form a monobromate and HBr
Chlorination uses what compound as a catalyst?

AlCl3

Iodization requires what?

An Acidic oxidizing agent such as HNO3 (yields NO2, I+, and H2O

Mechanism for nitration of benzene?

H2SO4 + HNO3 –> H2NO3+ + HSO4-
H2NO3+–> H20+ NO2+

Then NO2+ attacks carbon, and HSO4- attacks the hydrogen

Sulfonation of Benzene

SO3 attacks carbon, hydride shift places H on O to form Benzenesulfonic acid
Desulfonation occurs how?
Heating in dilute sulfuric acid
Toluene reaction vs Benzene?
Toluene reacts 25X faster since the CH3 activates the benzene ring (forms mostly Ortho and Para product)
Why does toluene favor ortho and para?
Due to the delocalization of the pi bonds, ortho and para offer positions in with tertiary carbons, which is favorable over the meta position which only only offers secondary.  Also, the energy for the compounds is significantly lower compared to meta.
What is induction when it comes to sigma complexes?
induction stablizes the sigma complex by donating electron density through the sigma bond.
What stablizes the sigma complex by Resonance?
Substituents with a lone pair of electrons.
Explain the reaction of aniline with bromine
Aniline reacts with bromine water (no catalyst) to form aniline tribromide (bromides in ortho and para due to the lone pair of electrons) and NaHCO3 is used to neutralize HBr that forms.
List the activators in order of reactivity

O-, N (R)2, OH, O(R), HNC=O(R), R

Oxides, Anilines, Phenols, Phenyl Ethers, Anilides, Alkylbenzenes

What is used to create Meta substituted benzenes?
Deactivating groups
Nitrobenzene vs Benzene reactiviy?
Nitrobenzene is 100000X slower than benzene
Why do deactivating groups favor meta?
because they deactivate all the positions around the ring, but they deactivate the meta positions LESS
What makes ortho and para positions for deactivating groups so unstable?
Whenever there is a deactivating complex and a substitution is being made, the 2 + charges are right across from eachother, resuting in alot of instability.
What are the characteristics a deactivating group can have?

A partial positive charge, as this sucks electron density out of the ring via the sigma bond, meaning it is less electron rich than benzene.

Name the deactivating groups (resulting in Meta)

NO2, SO3H, C(triple bond)N, O=C-R, O=C-O-R, N(R)3

Nitrobenzene, sulfonic acid, cyano, Ketone/Aldehyde, Ester, quaternary ammonium

What is special about Halobenzenes when it comes to substituent placement?
Halogen groubs deactivate the benzene ring, BUT they are conducive to ortho and para substitution.  They are electronegative and suck electron density through the sigma bond, but have 3 lone pairs which cause resonance in the ring and stablize the sigma complex.
How do halo benzenes react to ortho and para substitution?

A double bond forms with the hallogen (ex. bromonium ion) and it causes resonance.  Meta attacks leave no possiblity for bromonium ions.

What are some common reactants resulting in carbocations?
Benzene Cl2 and AlCl3, Alkenes and HF, Alcohols and BF3
Benzene+Alkylhalide+Lewis Acid=?
Alkylbenzene
When does an Alkylhalide and strong lewis acid subsitution fail?
when there is a deactivating complex stronger than a hallogen, or when the carbocation, resulting from the hallogen leaving for the lewis acid, rearranges.
What’s the problem with the alkylbenzene product of a Alkylhalide subsitution?
it’s more reactive than the benzene, so polyalkylation occurs.
Acylation is what?
Acyl chloride is used instead of an alkylhalide, resulting in the acylium ion which is resonance stabilized and doesn’t rearrange, the product is a phenyl ketone that is less reactive than benzene.
Write out or visualize the reaction for acylation
[image]
How do you turn an acyl benzene into an alkylbenzene?
Via amalgamated Zinc (Zn(Hg));and aqueous HCL

How do you form Formyl Chloride?

A High pressure mixture of CO, HCl, and then treated with AlCl3/CuCl to yield H-C+=O
What does formylation of Benzene yield?
benzaldehyde
How does one do a Nucleophilic Subsitution reaction?
A nucleophile replaces a leaving group on the ring, and the ring is activated by electron withdrawing substituents.
Write out or visualize the Benzyne Mechanism
[image]
Where does the name for the benzyne reaction come from?
Benzyne is an intermediate before the amine group attaches.
How does chlorination occur?
With high enough heat, pressure or light… the first chlorination is hard, but the next 2 moles are easy.
How does catalytic hydrogenation occur?
High temperature (100 C), high pressure (1000 PSI), and a catalyst of either Pt, Pd, Ni, Ru, or Rh. (it cannot be stopped at an intermediate stage, ring is completely hydrogenated)
Explain the Birch mechanism and how it works.
The birch mechanism begins when sodium reacts with amonia to form amonia, sodium ion, and free electrons.; The free electrons attack the carbons in the benzene ring, which form anions, which steal; protons from alcohol. It does this 2 times to form a 1,4-cyclohex ring

Detail the regiospecific birch reactions

when the benzene ring has an e- withdrawing group, the group is not attached to a double bond

when the benzene ring has a e- releasing group, the group is attached to a double bond.

alkylbenzene + ____ or______= 1,2 benzoic acid

HOT KMnO4, Na2Cr2O7/H2SO4

Explain the difference between the hallogens when reacting with an alkylbenzene.

Br2 reacts with the benzylic position only, while Cl2 results in mixtures.
Benzylhalide + alcohol=?
benzyl ether (alkyl from alcohol)

In terms of Sn2 reactions, how reactive is a benzylic halide;vs;primary halide;and why?

A benzylic halides are 100X more reactive than primary halides, this is caused by the fact that the transition state is stabilized by a ring.
Phenol + Carboxylic acid=?
Ester
Phenol+ ?=ester
Carboxylic acid
phenol+aqNaOH=?
phenoxide ion
Phenol+?=phenoxide ion
aqNaOH
Phenols an Phenoxides…
are highly reactive and will form tribromination without a catalyst, and even reacts with CO2
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