Arenes Flashcards
What is the simplest form of the arene functional group?
Benzene, C6H6
What is in the center of a benzene?
delocalised pi electron ring
Describe the structure of cyclohexa- 1,3,5 - triene
alternating carbon carbon double and single bonds
What is cyclohexa-1,3,5-triene and example of?
Kekule structure
Describe a Kekule structure
P-orbitals in each point
What is the orbital model?
hexagonal planer. C are trigonal planar. bond angle 120
pi bond
delocalised pi electron ring
two rings with a hexagon in the middle
Why can benzene not be an Kekule’s? (Bromine)
Because alkenes react with Br2 to make dibromoalkane orange –> colourless, whereas benzene doesn’t
Why can benzene not be Kekule’s? (bond length)
c-c bond = 0.154nm, c=c bond = 0.134nm
but the bonds in benzene are all 0.139nm
Why can benzene not be Kekule’s? (enthalpy)
enthalpy of hyrdrogenation of benzene = -208kJmol-1, cyclohexene = -120kJmol-1
cyclohexatriene should be -360kJmol-1 which is 153kJmol-1 less than expected
what is the prefix of benzene?
phenyl
Describe electrophilic addition in benzene
like normal electrophili addition
remember the ring turns into a horse-shoe shape with a + pointing towards the activation cite
name the activation cites on the benzene ring?
1 = x
2 = ortho
3 = meta
4 = para
What is x for ortho and para directing groups?
x = lone pair on the atom directly attached
example: alcohol, halide, group 6, group 5
exception: alkyl group, -CH3
What is x or meta directing groups?
x = y
example = aldehyde, ketone, carboxylic acid, ester, alkene, C=O, NO2
How do you produce strong electrophiles?
AlBr3 + Br2 –> AlBr4- + Br+
