Benzene / Benzene Derivative Reactions Flashcards
halogenation of aromatic compounds
does not undergo normal halogenation because aromatic ring is so stable
hydration of aromatic compounds
products higher in energy than reactants; not favorable
aromatic heterocycles lone pair interactions
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)
O vs S orbital overlap
O uses 2p orbital and S used 3p orbital; since 2p orbital is smaller better overlap with O -> stronger connection
Electrophilic Aromatic Substitution Reaction (gen steps)
- generate electrophile (aromatic structure acts as nucleophile)
- generate high energy intermediate (arenium cation)
- base takes off extra H -> sub product formed
EAS reaction kinetic or thermodynamic control
kinetic control;
*irreversible
*regioselectivity determined by the stability of the intermediate NOT end product
Bromination EAS rxn
– Br2, AlBr3 –>
generate electrophile by lewis acid/base rxn between Br2 and AlBr3
Chlorination EAS rxn
– Cl2, AlCl3 –>
*generate electrophile by lewis acid/base rxn between Cl2 and AlCl3
nitration EAS rxn
–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
Friedel- Crafts Alkylation
– 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
Alkylation alternative mech (not FC)
– alkene, H2SO4 –>
* carbocation intermediate formed which acts as electrophile
Friedel Crafts Acylation
– 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)
Alternate reagents for FC Acylation
anhydride; AlCl3 reacts with center O -> Acylium cation electrophile
What reaction can happened intramolecularly
Acylation; favorable to form 5 or 6 membered ring
sulfonation reaction
– SO3, H2SO4 –>
S in SO3 and SO3H is electrophilic
what is unique about sulfonation reaction
it is reversible
- steam, heat or very dilute H2SO4 (aq)
when does the group attach to the ortho/ para position
electron donating group already on ring; can interact in ortho/para potion with pi conj system -> stabilizing
when does the group attach to the meta position
electron withdrawing group already on ring; ortho and para position put pos charge on electron lacking carbon; build up of pos charge is unstable
activating group
makes ring more reactive relative to benzene; more electron rich, more nucleophilic, high energy
deactivating group
makes ring less reactive relative to benzene; less electron rich, less nucleophilic, lower energy
where will an activating group attach
ortho/ para
where will a deactivating group attach
meta
sigma e- donating/ withdrawing
deals with electronegativity and bond dipoles
pi e- donating/ withdrawing
deals with ability to donate e- to pi conj system to stabilize
activating/ deactivating: halogens
- size of p orbital (smaller orbital = better overlap)
*length of sigma bond (shorter bond = stronger)
