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Organic chemistry chapter 17
Organic chemistry review for Reactions of Aromatic compounds
46
Chemistry
Undergraduate 2
07/17/2008

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Term

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

Definition

basic

Term
Why does FeBr3 allow for bromination of the usually non-reactive benzene?
Definition
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
Term
Chlorination uses what compound as a catalyst?
Definition

AlCl3

Term

Iodization requires what?

Definition

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

Term

Mechanism for nitration of benzene?

Definition

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

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

Term

Sulfonation of Benzene

Definition
SO3 attacks carbon, hydride shift places H on O to form Benzenesulfonic acid
Term
Desulfonation occurs how?
Definition
Heating in dilute sulfuric acid
Term
Toluene reaction vs Benzene?
Definition
Toluene reacts 25X faster since the CH3 activates the benzene ring (forms mostly Ortho and Para product)
Term
Why does toluene favor ortho and para?
Definition
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.
Term
What is induction when it comes to sigma complexes?
Definition
induction stablizes the sigma complex by donating electron density through the sigma bond.
Term
What stablizes the sigma complex by Resonance?
Definition
Substituents with a lone pair of electrons.
Term
Explain the reaction of aniline with bromine
Definition
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.
Term
List the activators in order of reactivity
Definition

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

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

Term
What is used to create Meta substituted benzenes?
Definition
Deactivating groups
Term
Nitrobenzene vs Benzene reactiviy?
Definition
Nitrobenzene is 100000X slower than benzene
Term
Why do deactivating groups favor meta?
Definition
because they deactivate all the positions around the ring, but they deactivate the meta positions LESS
Term
What makes ortho and para positions for deactivating groups so unstable?
Definition
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.
Term
What are the characteristics a deactivating group can have?
Definition

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.

Term
Name the deactivating groups (resulting in Meta)
Definition

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

Term
What is special about Halobenzenes when it comes to substituent placement?
Definition
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.
Term
How do halo benzenes react to ortho and para substitution?
Definition

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

Term
What are some common reactants resulting in carbocations?
Definition
Benzene Cl2 and AlCl3, Alkenes and HF, Alcohols and BF3
Term
Benzene+Alkylhalide+Lewis Acid=?
Definition
Alkylbenzene
Term
When does an Alkylhalide and strong lewis acid subsitution fail?
Definition
when there is a deactivating complex stronger than a hallogen, or when the carbocation, resulting from the hallogen leaving for the lewis acid, rearranges.
Term
What's the problem with the alkylbenzene product of a Alkylhalide subsitution?
Definition
it's more reactive than the benzene, so polyalkylation occurs.
Term
Acylation is what?
Definition
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.
Term
Write out or visualize the reaction for acylation
Definition
[image]
Term
How do you turn an acyl benzene into an alkylbenzene?
Definition
Via amalgamated Zinc (Zn(Hg)) and aqueous HCL
Term

How do you form Formyl Chloride?

Definition
A High pressure mixture of CO, HCl, and then treated with AlCl3/CuCl to yield H-C+=O
Term
What does formylation of Benzene yield?
Definition
benzaldehyde
Term
How does one do a Nucleophilic Subsitution reaction?
Definition
A nucleophile replaces a leaving group on the ring, and the ring is activated by electron withdrawing substituents.
Term
Write out or visualize the Benzyne Mechanism
Definition
[image]
Term
Where does the name for the benzyne reaction come from?
Definition
Benzyne is an intermediate before the amine group attaches.
Term
How does chlorination occur?
Definition
With high enough heat, pressure or light... the first chlorination is hard, but the next 2 moles are easy.
Term
How does catalytic hydrogenation occur?
Definition
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)
Term
Explain the Birch mechanism and how it works.
Definition
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
Term

Detail the regiospecific birch reactions

Definition

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.

Term

alkylbenzene + ____ or______= 1,2 benzoic acid

Definition

HOT KMnO4, Na2Cr2O7/H2SO4

Term

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

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

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

Definition
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.
Term
Phenol + Carboxylic acid=?
Definition
Ester
Term
Phenol+ ?=ester
Definition
Carboxylic acid
Term
phenol+aqNaOH=?
Definition
phenoxide ion
Term
Phenol+?=phenoxide ion
Definition
aqNaOH
Term
Phenols an Phenoxides...
Definition
are highly reactive and will form tribromination without a catalyst, and even reacts with CO2
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