Aromatic compounds

Question 1

There are two major classes of organic chemicals

Answer 1

aliphatic: straight or branched chain organic substances

aromatic or arene: includes one or more ring of six carbon atoms with delocalized bonding

Question 2

Benzene’s Structure

Answer 2

The simplest arene is benzene. It has the molecular formula C6H6 Its basic structure is six C atoms in a hexagonal ring, with one H atom bonded to each C atom. Each C atom is bonded to two other C atoms and one H atom by single covalent σ-bonds. This leaves one unused electron on each C atom in a p orbital, perpendicular to the plane of the ring. The Six p electrons are delocalised in a ring structure above and below the plane of carbon atoms

Question 3

proof of delocalisation

Answer 3

Benzene is a planar molecule. The evidence suggests all the C-C bonds are the same and have a length and bond energy between a C-C single and C=C double bond.

Question 4

Using Enthalpies of Hydrogenation to show Thermodynamic Stability

Answer 4

Question 5

Reactions of Benzene

Answer 5

Benzene does not generally undergo addition reactions because these would involve breaking up the delocalised system. Most of Benzene’s reactions involve substituting one H for another atom or group of atoms. Benzene has a high electron density and so attracts electrophiles. It reactions are usually electrophilic substitutions.

Question 6

Toxicity of Benzene

Answer 6

Benzene is a carcinogen (cancers causing molecule) and is banned for use in schools. Methylbenzene is less toxic and also reacts more readily than benzene as the methyl side group releases electrons into the delocalised system making it more attractive to electrophiles.

Question 7

Nitration of Benzene

Answer 7

Question 8

Friedel Crafts Acylation

Answer 8

Question 9

Reducing a Nitroarene to aromatic amines

Answer 9

Question 10

Effect of delocalisation on side groups with lone pairs

Answer 10