Reaction Reagents 7

Question 1

What makes benzene so unreactive?

Answer 1

stabilized by resonance of 3 pi bonds, so not e- rich = AROMATIC STABILITY

Question 2

What are the 2 criteria for aromatic compounds?

Answer 2

1. fully conjugated ring with overlapping p orbitals (every atom sp2 in ring or has resonance structure with anion/cation)
2. have 4n+2 = total pi electrons

Question 3

if a lone pair in a ring is needed for aromaticity then…

Answer 3

the lone pair is not as basic

Question 4

what are the positions for derivatives of benzene that contain 2 substituents called?

Answer 4

1, 2 substituent position = ortho
1,3 = meta
1,4 = para

Question 5

What is the benzylic position? How is it stabilized?

Answer 5

one C away from benzene

charge delocalized and stabilized if anion or cation, or group by resonance = more acidic

Question 6

benzene with benzylic C + chromic acid (H2CrO4)

Answer 6

benzylic position C with at least 1H mixed with chromic acid oxidizes the C

= carboxylic acid

** not H on benzylic C = NR

Question 7

benzene + H2CrO4

Answer 7

no rxn (not easily oxidized)

Question 8

alkane/alkyl group + H2CrO4

Answer 8

no rxn (not easily oxidized)

Question 9

benzene + KMnO4

Answer 9

no reaction

Question 10

benzene with benzylic C + KMNO4 + H2O

Answer 10

MnO4- oxidizes benzylic C

acidic water protonates

carboxyl group

KMnO4 and H2CrO4 are oxidizing agents

Question 11

The p bonds of aromatic rings are not easily oxidized, but

Answer 11

benzylic carbons, are oxidized to carboxylic acids if they are bonded to one or more H.

Question 12

benzene + E+ (electrophilic aromatic substitution)

Answer 12

pi bond nuc attacks electrophile (one C has E+ and other C is carbocation)

base takes on H that was on the C of the C=C (elimination rxn)

reform double bond/reformed aromatic ring

Question 13

halogenation of benzylic C on a benzene?

Answer 13

MAKE E+(Br+):

Br2 + FeBr3:

one Br attacks Fe making intermediate

middle Br is EWG, other Br becomes Br+

RXN:
pi bond attacks Br in intermedate (Br+)

carbocation rerrangement in sigma complex intermediate

base (remaining intermediate: Br-FeBr3) attacks H making HBr and FeBr3

aromatcity restored

FeBr3 is a Lewis acid, could also be AlBr3

this could also be cholrination with Cl2 and AlCl3

Question 14

sulfonation of benzylic C on a benzene?

Answer 14

Make E+ (SO3)
fuming H2SO4: base sulfuric acid attacks acidic sulfuric acid

RXN
pi bond attacks S of SO3 making carbocation

carbocation rearrangement in sigma complex

H2O formed from making E+ deprotonates benzylic C making H3O+

aromaticity restored

SO3- group’s O on benzene attacks H on H3O+ making SO3H group on benzene

Question 15

what is unique about sulfonation?

Answer 15

reversible:
conc H2So4 = SO3H group
dilute H2So4 = benzene

Question 16

nitration of benzylic C on benzene?

Answer 16

Make E+ (NO2):
HNO3 + H2SO4 makes NO2+ = E+

RXN
pi bond attacks N on NO2

carbocation rearrangement in sigma complex

water formed from making E+ basic attacks benzylic C’s H reforming aromaticity

Question 17

nitration can be reduced to make…

Answer 17

amines (aniline)

benzene + NO2 -> benzene + NH2

Question 18

aniline rxn of benzylic C on benzene?

Answer 18

benzene + 1)HNO3/H2SO4 to make nitration (NO2)

2) Fe or Zn, HCl to make benzene _ NH3+

3) NaOH base takes H

benzene + NH2

Question 19

What is alkylation?

Answer 19

benzene + alkyl halide + lewis acid = alkyl group on benzene

Question 20

Friedel-Crafts Alkylation mechanism? What is necessary for this reaction to occur?

Answer 20

make E+ (carbocation):
alkyl halide + AlCl3: X attacks Al making intermediate with +ve charged Cl which is EWG -> carbocation group leaves = E+
(also makes AlCl4- base)
this carbocation can be rearranged

RXN:
pi attack carbocation E+

sigma complex carbocation rearrangement

Cl of AlCl4- base attacks H in benzylic position reforming aromatic ring

necessary: halide LG is attached to sp3 carbon

Question 21

alkylation of alkene to a benzylic position C?

Answer 21

make E+:
- alkene + H3PO4 (atrong non-nucleophilic acid)
- alkene attacks one H of H3Po4
- carbocation rearrangement

RXN
- pi bond attacks carbocation
- H2PO4- deprotonates to reform aromaticity

Question 22

Friedel-Crafts Acylation benzylic position C rxn?

Answer 22

benzene + lewis acid + acyl halide (ketone with R grp and X)

Question 23

Acylation and alkylation both…

Answer 23

for new C-C bonds

Question 24

Friedel-Crafts Acylation benzylic position C rxn mechanism?

Answer 24

make E+
- acyl halide X attacks Al of AlCl3
- intermediate forms, Cl is EWG and +ve charge
- R-C(+)=O –> R-C≅O(+) acylium ion = E+

RXN:
- pi bond attacks C of acylium ion
- sigma complex carbocation rearrangement
- Cl of AlCl4- from E+ formation attacks H to reform aromaticity

forms aryl ketone/aldehyde