Benzene / Benzene Derivative Reactions

Question 1

halogenation of aromatic compounds

Answer 1

does not undergo normal halogenation because aromatic ring is so stable

Question 2

hydration of aromatic compounds

Answer 2

products higher in energy than reactants; not favorable

Question 3

aromatic heterocycles lone pair interactions

Answer 3

lone pair can either be separate from pi conj system, (ex. pyridine) or it can be involved in the pi conj system (ex. furan; O)

Question 4

O vs S orbital overlap

Answer 4

O uses 2p orbital and S used 3p orbital; since 2p orbital is smaller better overlap with O -> stronger connection

Question 5

Electrophilic Aromatic Substitution Reaction (gen steps)

Answer 5

• generate electrophile (aromatic structure acts as nucleophile)
• generate high energy intermediate (arenium cation)
• base takes off extra H -> sub product formed

Question 6

EAS reaction kinetic or thermodynamic control

Answer 6

kinetic control;
*irreversible
*regioselectivity determined by the stability of the intermediate NOT end product

Question 7

Bromination EAS rxn

Answer 7

– Br2, AlBr3 –>
generate electrophile by lewis acid/base rxn between Br2 and AlBr3

Question 8

Chlorination EAS rxn

Answer 8

– Cl2, AlCl3 –>
*generate electrophile by lewis acid/base rxn between Cl2 and AlCl3

Question 9

nitration EAS rxn

Answer 9

–HNO3, H2SO4, H20–> H2O and product
*generate electrophile by acid base rxn between HNO3 (base) and H2SO4 (acid); NO2 electrophile
* water acts as base to deprotonate aromatic ring

Question 10

Friedel- Crafts Alkylation

Answer 10

– Cl-alkyl group, AlCl3–> HCl and product
*generate electrophile same as chlorination, Sn2 rxn between electrophile and nucleophile
**product higher energy than SM -. further react; prone to over alkylation AND rearagemement

Question 11

Alkylation alternative mech (not FC)

Answer 11

– alkene, H2SO4 –>
* carbocation intermediate formed which acts as electrophile

Question 12

Friedel Crafts Acylation

Answer 12

– 1)carbonyl- Cl, 2)H2O–>
* no rearrangements AND products lower energy than SM
*electrophile: Cl bonds to Al -> AlCl4- and Ch3 C triple bond electrophile
* H20 turns AlCl3 -> Al(OH)3 stop further reaction
*must ass more than 1 equv. of AlCl3 (not catalytic amount)

Question 13

Alternate reagents for FC Acylation

Answer 13

anhydride; AlCl3 reacts with center O -> Acylium cation electrophile

Question 14

What reaction can happened intramolecularly

Answer 14

Acylation; favorable to form 5 or 6 membered ring

Question 15

sulfonation reaction

Answer 15

– SO3, H2SO4 –>
S in SO3 and SO3H is electrophilic

Question 16

what is unique about sulfonation reaction

Answer 16

it is reversible
- steam, heat or very dilute H2SO4 (aq)

Question 17

when does the group attach to the ortho/ para position

Answer 17

electron donating group already on ring; can interact in ortho/para potion with pi conj system -> stabilizing

Question 18

when does the group attach to the meta position

Answer 18

electron withdrawing group already on ring; ortho and para position put pos charge on electron lacking carbon; build up of pos charge is unstable

Question 19

activating group

Answer 19

makes ring more reactive relative to benzene; more electron rich, more nucleophilic, high energy

Question 20

deactivating group

Answer 20

makes ring less reactive relative to benzene; less electron rich, less nucleophilic, lower energy

Question 21

where will an activating group attach

Answer 21

ortho/ para

Question 22

where will a deactivating group attach

Answer 22

meta

Question 23

sigma e- donating/ withdrawing

Answer 23

deals with electronegativity and bond dipoles

Question 24

pi e- donating/ withdrawing

Answer 24

deals with ability to donate e- to pi conj system to stabilize

Question 25

activating/ deactivating: halogens

Answer 25

• size of p orbital (smaller orbital = better overlap)
  *length of sigma bond (shorter bond = stronger)