Aromatic Chemistry

Question 1

What is the molecular formula of Benzene?

Answer 1

C6H6

Question 2

Draw the Kekulé structure of Benzene?

Answer 2

Page 126 in text book

Question 3

Explain why Kelulké’s structure is unusual and how it differs from an unsaturated alkene with an example.

Answer 3

Structure suggests benzene should react like an unsaturated alkene but instead it does not e.g.requires vigorous conditions and a catalyst whereas Alkenes react with aqueous bromine solution

Question 4

True or false the evidence formed by keluké’s structure shows Benzene as being less reactive than an alkene? Explain answer.

Answer 4

True because it has no reaction with aqueous bromine solution unlike alkenes

Question 5

What is the IUPAC name for Keluké’s structure?

Answer 5

Cyclohexa-1,3,5-triene

Question 6

Explain why the enthalpy of hydrogenation proves that Benzene is more stable than cyclohexane-1,3,5-triene?

Answer 6

Cyclohexene has an enthalpy of hydrogenation (EH) of 119kjmol-1 therefore cyclohexane-1,3,5-triene predicts that the EH of Benzene would be -119 x 3=357.
However the EH of Benzene is 208kjmol-1 so Benzene is actually 149kjmol-1 more stable than cyclohexa-1,3,5-triene

Question 7

What would you call the extra stability of Benzene in comparison to Cyclohexa-1,3,5-Triene

Answer 7

Delocalisation energy of Benzene

Question 8

Benzene contains alternating C=C and C-C bonds? True or False?

Answer 8

False

Question 9

How can the cyclic structure Benzene be confirmed?

Answer 9

X-ray diffraction

Question 10

What are the Bond lengths in Benzene Alkene and Alkanes?

Answer 10

Benzene bond lengths is 0.140nm all around.
Alkene is 0.134nm
Alkane is 0.154nm

Question 11

The fourth bonding electron is shared in a…

Answer 11

Pi Bond.

Question 12

The ___ Bonds of the six ______ atoms overlap and the six ____________ atoms are shared in a d_________-shaped electron cloud above and below the _______ of the flat hexagon of carbon. The electrons in the pi bonds are said to be_______________ making Benzene more stable that Cyclohexa-1,3,5-triene.

Answer 12

Pi
Carbon
Doughnut
Plane
Delocalised

Question 13

What group replaces hydrogen atoms on benzene when benzene undergoes nitrafication?

Answer 13

-NO2 replaces one of the hydrogen atoms

Question 14

What ion is generated by mixing concentrated nitric acid and concentrated sulphuric acid and heating to 50 degrees?

Answer 14

Nitronium ion (NO2+)

Question 15

What is produced when the concentrated sulfuric acid donates a proton to nitric acid .

Answer 15

An intermediate of [H2NO3]+ which
decomposes to yield the electrophillic nitronium ion ( you can see on page 129 text book)

Question 16

In the Nitrafication of Benzene sulfuric acid also acts as a________ in the reaction.

Answer 16

A catalyst as it is regenerated when the HSO4- ion reacts with the H+ ion released in the last step it the reaction mechanism.

Question 17

Nitro group can be reduced to…..

Answer 17

Amine group

Question 18

What are the uses of Aromatic Amines?

Answer 18

Can be used in the dye industries or other industries

Question 19

How can reduction be achieved for nitrobenzene?

Answer 19

Reduction can be achieved using iron, tin with conc hydrochloric acid or they can use catalytic hydrogenation with nickel and hydrogen gas