18a: arenes - benzenes Flashcards
what are arenes?
ring of hydrocarbons / ring with carbon atoms in which has delocalised e-
what does kekule’s model suggest in terms of the structure of benzene?
3 double bonds & 3 single bonds alternating in a ring
what is the shape of a benzene?
planar hexagon
what is the bond angle in benzenes?
120
what does the delocalised model of benzene suggest in terms of structure?
all C-C bonds are the same
how does the orbitals from carbon atoms interact to form the bonds in a benzene ring?
1- end-on-end overlapping between p-orbitals from neighbouring C atoms to form a sigma bond
2- 6 delocalised e- were shared equally
how does the difference in enthalpies of hydrogenation supports the delocalised structure?
real enthalpy is less than predicted value
-> due to 6 pi-orbital e- are delocalised & not arranged in double bonds -> more thermodynamically stable
list all intermolecular forces in benzenes.
weak London forces
what type of flame is observed when benzenes combust? why?
sooty/smokey flame due to low C:H ratio
what are the reagents, conditions & mechanism of bromination of benzenes?
mechanism: electrophilic substitution
reagent: Br2
conditions: room temp. & FeBr3 catalyst
what are the reagents, conditions & mechanism of chlorination of benzenes?
mechanism: electrophilic substitution
reagent: Cl2
conditions: room temp. & FeCl3 / AlCl3 catalyst
draw the mechanism of electrophilic substitution of benzenes with bromine. *
draw the mechanism of nitration of benzenes. *
what are the reagents, conditions & mechanism of nitration of benzenes?
mechanism: electrophilic substitution
reagents: conc. HNO3 & conc. H2SO4 catalyst
conditions: below 55C
what is the mechanism of friedel-crafts reactions?
electrophilic substitution
what are the reagents and conditions of friedel-crafts alkylation?
reagent - RCl (chloroalkyl compound)
conditions - anhydrous AlCl3 catalyst
- heat under reflux
draw the mechanism of friedel-crafts alkylation. *
what are the reagents & conditions of friedel-crafts acetylation?
reagents - acyl chloride
conditions - anhydrous AlCl3 catalyst
- heat under reflux at 50C
draw the mechanism of friedel-craft acetylation. *
describe how the reactivity of the OH group & ring is changed in a phenol group.
lone pair of e- on O is delocalised with charge cloud
why does phenol reacts with NaOH?
weakly acidic
describe the reagents and conditions of bromination of phenols.
reagents - bromine water
conditions - room temp.
draw the mechanism of bromination of phenols. *
why does phenols not require a halogen carrier?
lone pair on O on -OH group is partially delocalised in the ring & activates the ring
-> higher e- density & Br2 is more polarised
how could 2,4,6-tribromophenol be identified?
white solid, antiseptic smell
