Benzene and Electrophile Aromatic Substitution

Question 1

Halogenation of Benzene

Answer 1

Br-Br(+)-Fe(-)Br3 (Lewis acid catalyst, also works with Cl and FeCl3)
Carbocation intermediate formed
Adds one halogen
Catalyst regenerated

Question 2

Nitration of Benzene

Answer 2

O=N(+)=O
Carbocation intermediate formed
Adds NO2, N has (+) formal charge, one O has (-) formal charge, and one O is double bonded to N

Question 3

Sulfonation of Benzene

Answer 3

Sulfur trioxide, H2SO4
Have to protonate an O in SO3 before reacting
Adds sulfonic acid (SOOOH)
Reversible w/ reactants H2SO4 and H2O at 100 degrees Celsius

Question 4

Friedel-Crafts Alkylation of Benzene

Answer 4

• Use AlCl3 and an alkane w/ Cl to produce a carbocation alkane Lewis acid catalyst
• Need excess benzene as a SM to prevent over-alkylation
• Forms carbocation intermediate
• Adds the alkyl group and regenerates catalyst (AlCl3) and HCl

Question 5

Friedel-Crafts Acylation of Benzene

Answer 5

• Use stoich amount of AlCl3 and carbonyl w/ halogen to produce acylium ion (carbon chain triple bonded to O, O has lone pair and (+) formal charge)
• Forms carbocation intermediate
• Adds carbonyl group (ketone)

Question 6

Hydrogenation of the Benzene Ring with H2 and Pd/C

Answer 6

• No reaction b/c it’s too stable

Question 7

Hydrogenation of the Benzene Ring with Ni, excess H2, heat

Answer 7

• Produces cyclohexane

Question 8

Reactivity of Benzylic position: H2, Pd/C

Answer 8

Attacks carbonyl at benzylic position, leaves any others

Question 9

Reactivity of Benzylic position: 1. Zn/Hg amalgam 2. HCl, heat

Answer 9

Eliminates all carbonyls

Question 10

Reactivity of the Benzylic Position: 1. NBS, H2O2 2. heat

Answer 10

Adds Br to benzylic position

Question 11

Activating groups add…

Answer 11

ortho/para

Question 12

Deactivating groups add…

Answer 12

meta

Question 13

Halogens as a benzene substituent

Answer 13

Deactivating, add ortho/para

Question 14

-NH2 or -NR2 as a benzene substituent

Answer 14

Activating, add ortho/para

Question 15

-OH, -OR as a benzene substituent

Answer 15

Activating, add ortho/para

Question 16

-R (alkyl groups) as a benzene substituent

Answer 16

Activating, add ortho/para

Question 17

-Ph (phenyl groups) as a benzene substituent

Answer 17

Activating, add ortho/para

Question 18

Carboxylic acids, -CONH2, -COOR as benzene substituents

Answer 18

Deactivating, add meta

Question 19

-COR (acyl groups) as a benzene substituent

Answer 19

Deactivating, add meta

Question 20

-SO3H (sulfonic acid), -CN (cyano groups), -NO2 (nitro groups), -(+)NR3 (ammonium groups) as a benzene substituent

Answer 20

Deactivating, add meta