Aromatic Chemistry Flashcards
what is the basic structure of benzene
cyclic planar molecule with the formula c6h6
why are all the bond lengths same
due to the delocalised electron structure all of the c-c bonds are the same length
what do the lone electrons in the p orbitals combine to form
delocalised ring of electrons
whys benzene more stable then theroetical alternative cyclohexa-1,3,5-triene
enthalpy change of hydrogenation
cyclohexene has one double bond so it is -120,
benzene has 3 double bonds so it is expected to be -360 however it is actually -208 which is the experimental value.
this is because energy required to break the bond and energy is released to form bonds which suggests that more energy is required to break bonds in benzene than in cyclohexa-1,3,5-triene
benzene is also more stable due to the delocalised electron structure
what is the reaction of arenes (benzene)
electrophilic substitution
how is benzene attracted to the electrophile
benzene has an high electron density so has a delocalised ring of electrons which attracts electrophiles
what are the two mechanisms benzene undergoes
- friedels crafts acylation
- nitration of benzene
Friedel’s crafts acylation:
change in functional group
mechanism
reagent
conditions
benzene —– phenyl ketone
electrophilic substitution
acyl chloride in the presence of anhydrous alcl3 catalyst
heat under reflux
electrophile for Friedel’s crafts
alcl3 + ch3cocl ——> (ch3co)+ + (alcl4)-
nitration of benzene
change in functional group
mechanism
reagent
electrophile
benzene —> nitrobenzene
electrophilic substitution
concentrated nitric acid in the presence of concentrated sulfuric acid catalyst
NO2+
Electrophile for nitration
HNO3 + H2SO4 —–> H2NO3+ + HSO4-
H2NO3+ —-> NO2+ + H2O
What happens to the H+ THAT IS FORMED IN ELECTRO[HILLIC SUBSTITUON
it reacts with HSO4- to make h2so4
why does it have to take place in an ice bath
to stop multiple nitration’s from occurring
