Klein - 19

Front 1

Describe generally three types of reactions that can occur on an aromatic ring like a benzene ring?

Back 1

1.Electrophilic aromatic substitution: most common type. Benzene ring has a large electron density on it so it want to attack epecies with positive charge (electrophiles) to create a TS with positive charge called sigma complex / 2.Nucleophilic aromatic substitution: on a few cases when ring has powerful electron-withdrawing groups like NO2, nuclephiles attack ring to create a TS with negative charge called Meisenheimer complex / 3.Elimination-addition: rarely on high heat or very strong base, benzyne forms

Front 2

Describe electrophilic aromatic substitution? (nature of reaction, TS)

Back 2

Benzene ring has a large electron density on it so it want to attack species with positive charge (electrophiles) . the TS is called sigma complex and has positive charge. Postivie would be on ortho and para position in regard to the electrophile

Front 3

Describe nucleophilic aromatic substitution? (nature of reaction, TS)

Back 3

in a few cases when ring has powerful electron-withdrawing groups like NO2, nuclephiles attack the ring. the TS is called Meisenheimer complex and negative charge on ortho and para position (in regard to the nucleophile)

Front 4

Define Elimination-addition reaction on benzene ring? (nature of reaction, TS)

Back 4

rarely on high heat or very strong base. TS is called benzyne

Front 5

Define sigma complex (or arenium ion)?

Back 5

In a typical aromatic substitution reaction, the aromatic moiety functions as a nucleophile and attacks the electrophilic agent, generating a positively charged intermediate called a sigma complex, or arenium ion

Front 6

What reaction can be used as blocking reagent in the installation of functional groups on benzene ring?

Back 6

Sulfonation. Because it is easily reversible

Front 7

How to install nitro group (NO2) on a benzene ring?

Back 7

By Nitration (electrophilic aromatic substitution)

Front 8

HNO3 and H2SO4 create one electrophile suitable for installation on the benzene ring. Explain mechanism?

Back 8

Front 9

What type of reaction is? What's the product?

Back 9

Reduction of NO2 to NH2 (on a benzene ring)

Front 10

How to install a NH2 group on benzene ring?

Back 10

Two step is necessary: (1) nitration, followed by (2) reduction of the nitro group

Front 11

Define a typical Friedel–Crafts alkylation?

Back 11

Front 12

Type of reaction? Product?

Back 12

Friedel–Crafts alkylation (rearrangement is possible so major product would form from secondary carbocation not primery)

Front 13

Explain three limitations of Friedel–Crafts alkylation?

Back 13

1.the carbon atom connected to the halogen must be sp3 hybridized (in alkyl halide, meaning vinyl and aryl halides will not work) / 2.polyalkylations often occur / 3. Ring should not be attached to strong and moderate deactivators (Especially NO2)

Front 14

Define Friedel-Crafts Acylation?

Back 14

Front 15

What is acylium ion?

Back 15

Front 16

Define Clemmensen reduction?

Back 16

a zinc amalgam and HCl, the carbonyl group is completely reduced and replaced with two hydrogen atoms

Front 17

Propose a way to install the indicated alkyl chain on the benzene ring?

Back 17

1) Friedel-Crafts Acylation 2) Clemmensen reduction

Front 18

Rearrangement and polyalkylation are possible in Friedel-Crafts alkylation. What about Friedel-Crafts Acylation?

Back 18

1.Rearrangme is impossible 2.polyacylation is impossible (acyl group is a ring deactivator)

Front 19

Strong and moderate deactivating groups prevent Friedel-Crafts alkylation. Discuss the effect of deactivators on Friedel-Crafts acylation

Back 19

Any type of deactivator (Strong, Modearate and weak) prevents Friedel-Crafts acylaiton.

Front 20

Benzene activating groups can be organized in three categories. What are they?

Back 20

Activators increase electron density on benzene ring: 1.Strong (presence of a lone pair immediately adjacent to the aromatic ring e.g OH, OR, NR2) / 2.moderate (a lone pair that is already delocalized outside of the ring e.g. COO, CON) / 3.weak (alkyl chain)

Front 21

Benzene deactivating groups can be organized in in three categories. What are they ?

Back 21

Deactivators reduce electron density on the benzene ring: 1.Strong (NO2, NR3+, -CX3 when X is a halide) / 2.moderate: pull away electron density by resonance (pi bond adjacent to ring) 3.weak: Halides

Front 22

Explain directing effect of substitutions on a benzene for the upcoming substitutions?

Back 22

1. Activatos direct to ortho and para (Para is major due to steric effects) / 2.deactivators direct to meta except for Halides which direct to ortho and para

Front 23

Why halides direct to ortho and para regardless of the fact that they are deactivating group?

Back 23

There two opposite effects resonance and induction: for the ring the induction wins ( => pull away electron density on ring) but for the stability of Positive charge Resonance wins (=> direct to ortho and para)

Front 24

What is the results of the nitration (HNO3, H2SO4) of the following compound?

Back 24

It does lead to nitration because The reagents for nitration (a mixture of HNO3 and H2SO4) can oxidize the amino group, often leading to a mixture of undesirable products

Front 25

What is the product of the reaction of the following compound with CH3Cl, AlCl3?

Back 25

A Friedel-Crafts reaction (either alkylation or acylation) cannot be accomplished on rings that are either moderately or strongly deactivated.

Front 26

nucleophilic aromatic substitution can occur when three requirements exist. What are they?

Back 26

1.The ring must contain a powerful electron-withdrawing group (typically a nitro group which can to stabilize negative charge on the TS by resonance and inductive effect)./ 2.The ring must contain a good leaving group (usually a halide) / 3.The leaving group must be either ortho or para to the electron-withdrawing group (so by resonance the resulting negative charge comes under powerful electron-withdrawing group to get stabalized)

Front 27

Back 27

Snar [1.The ring must contain a powerful electron-withdrawing group (typically a nitro group which can to stabilize negative charge on the TS by resonance and inductive effect)./ 2.The ring must contain a good leaving group (usually a halide) / 3.The leaving group must be either ortho or para to the electron-withdrawing group (so by resonance the resulting negative charge comes under powerful electron-withdrawing group to get stabalized)]

Front 28

What is Meisenheimer complex?

Back 28

The TS with negative charge resulted from Nucleophilic attack on benzene ring

Front 29

Back 29

No reaction (No e-withdrawing group to undergo SNar / not enough heat to undergo Elimination-addition via benzyne intermediate)

Front 30

Back 30

No e-withdrawing group to undergo SNar but enough heat to undergo Elimination-addition via benzyne intermediate

Front 31

Back 31

No e-withdrawing group to undergo SNar but very strong base (NH2-) make it undergo Elimination-addition via benzyne intermediate even not in high temperature

Front 32

Benzyne

Back 32