Benzene

Question 1

Kekule structure

Answer 1

C₆H₆ ring
alternate single and double bonds between C atoms

Question 2

evidence against kekule structure (4)

Answer 2

reaction with bromine
infrared spec.
bond length
enthalpy of hydrogenation

Question 3

what does the reaction between benzene and bromine tell us about the bonding

Answer 3

benzene does not undergo addition readily with bromine, only substitution
unless it is under extreme conditions
showing that benzene does not contain double bonds

Question 4

infrared spectroscopy data of benzene

Answer 4

shows no absorbance for C-C or C=C bonds

Question 5

what C-C bond length of 0.14nm tells us about the structure

Answer 5

C-C is usually 0.154nm
C=C is usually 0.134nm
therefore it is beteen the two and all are evenly spread

Question 6

how predicted enthalpy change for hydrogenation of benzene and actual value differ and what this says

Answer 6

ecpected to be 3x enthalpy for hydrogenation of cyclohexane (-320KJmol^-1)
is actually 152 KJmol^-1 more stable due to the delocalised ring

Question 7

nitration of benzene equation

Answer 7

{o} + NO₂⁺ > {o}^_/NO₂ + H⁺

Question 8

formation of nitronium ion equation

Answer 8

HNO₃ + 2 H₂SO₄ > NO₂⁺ + 2 HSO₄^- + H₃O⁺

Question 9

nitration of benzene type of reaction

Answer 9

electrophilic substitution

Question 10

nitration of benzene steps

Answer 10

circle of benzene > NO₂⁺
C-H in ring > + with half circle around it
{o}^/NO₂ + H⁺

Question 11

why temperature needs to be controlled in nitration of benzene

Answer 11

so that further nitration does not occur

Question 12

what nitrobenzene can be used to make

Answer 12

explosives
aromatic amines for dyes

Question 13

equation for reaction of benzene and ethanoyl chloride

Answer 13

{o} + CH₃COCl > {o}^_/C(=O)CH₃ + HCl

Question 14

formation of electrophile for acylation of benzene equation

Answer 14

CH₃COCl + AlCl₃ > CH₃C₊=O + ACl₄^-

Question 15

acylation of benzene mechanism

Answer 15

{o} RC₊=O
ring > C₊ of RC₊=O
{(+}^/(H)C(=O)R
C-H on ring > positive charge inside half circle
{o}^/C(=O)R + H⁺

Question 16

reformation of catalyst in acylation of benzene equation

Answer 16

H⁺ + AlCl₄^- > AlCl₃ + HCl

Question 17

actual bonding of benzene diagram

Answer 17

6 C’s with figure 8’s
dotted lines connecting figure 8’s top and bottom

Question 18

Why delocalisation makes the benzene molecule more stable

Answer 18

electron density becomes more evenly spread therefore it is less likely to undergo electrophilic attack

Question 19

why benzene undergoes substitution rather than addition reactions

Answer 19

the delocalised ring of electrons is not broken as it is energetically favourable