aromatic chemistry

Question 1

what is the formulae for benzene ?

Answer 1

C6H6

Question 2

describe the bonding inside benzene and what this leads to?

Answer 2

Each carbon bonds to 2 carbons and 1 hydrogen convalently.
this leaves one electron unpaired. this electron is on the p orbital and sticks out of the ring plane.
the p orbitals of each carbon join together to form a ring of delocalised electron
all the carbon carbon bonds lie between 154pm (c-c bond) and 135pm (c=c bond)

Question 3

what is the alternative to benzene ?

Answer 3

cyclohexa 135 triene

Question 4

what proves benezene is more stable than cyclohexa 135 triene?

Answer 4

the hydrogenation of one of the double bonds of cyclohexa 135 triene is -120kjmol using this u would expect the hydrogenation of benzene to be -360kjmol-1 but it is actually much smaller -208kjmol. this means it is less exothermic so more energy is required to break benzene bonds than cyclohexa 135 triene.
this indicates benzene is more stable possibly due to its delocalised electron rings

Question 5

what is phenol and phenylamine

Answer 5

phenol= oh bonded with benzene
phenylamine = nh2 bonded with benzene

Question 6

why do arenes such as benzene undergo electrophillic substitution?
and what are the 2 reactions?

Answer 6

Benzene has a ring of electron density that attracts electrophiles
however as benzene is stable electrophillic addition doesnt occur
instead they undergo electrophilllic substituion where a hydrogen is replaced for a electrophile
the 2 reaction are:
Friedel-crafts acylation
nitration

Question 7

describe the steps of Friedel-crafts acylation?

Answer 7

A strong electrophile (carbocation) is needed this happens through acyl chloride reacting with a carrier halogen ALCL3
cl
R-c=o + ALCL3-> R-C+=O + ALCL4-
the carbocation then moves to break the benzene ring
2 delocalised electrons move from the benzene to the Carbocation leaveaing a positive charge inside the ring
The ALCL4- is attracted to the positive charge ring and one CL bonds with the H
This reproduced ALCL3 +HCL
This proves ALCL3 is a catalyst for this reaction
The electrons from C-H bond neutralise the positive charge and reform the ring structure

Question 8

describe the steps for nitration of benzene?

Answer 8

first you must make a strong electrophile
HNO3+ H2SO4-> H2NO3+ + HSO4-
the H2NO3+ decomposes to form NO2+ +H2O
NO2+ is the electrophile
2 delocalised electrons in the benzene ring move towards it producing a positive charge inside the ring
the electrons from the c-h move back towards the benzene ring leaving a H+
this H+ can recombing with HSO4- making H2SO4
this proves H2SO4 is a catylst for this reaction

Question 9

describe the conditions for the reaction of nitration of benzene?

Answer 9

Must be under 55 degrees to avoid multiple substiutions

Question 10

what are the uses of nitrobenzene?

Answer 10

dyes and pharmaceuticals can be made by reducing nitrobenzene to aromatic amines
Explosives can be made from nitrobenzene e.g 246trinitromethylbenzene also known as trinitrotoluene (TNT)

Question 11

Equation for the production of no2+ ions?

Answer 11

H2SO4 + HNO3 ->NO2- + H2O + HSO4-