3.3.10 aromatic chemistry

Question 1

what are arenes

Answer 1

aromatic hydrocarbons which contain a benzene ring.

Question 2

what is benzene

Answer 2

the simplest arene with a molecular formula of C6H6, which is composed of a hexagonal structure and a central ring of electrons.

Question 3

how is the ring of electrons formed

Answer 3

each carbon is bonded to one hydrogen and two other carbons, leaving one delocalised electron. the overlap of electrons forms a ring and gives the molecule stability

Question 4

evidence for the delocalised model (x rays)

Answer 4

x rays showed that all C-C bonds where the same in length at 140pm. the value is between the typical length of a C-C bond and a C=C bond.
this disproves the Kekulé model, as it suggests double bonds.

Question 5

evidence for the delocalised model (electrophilic addition)

Answer 5

benzene is resistant to electrophilic addition reactions e.g. decolourising bromine water.
the preposed kekulé model would decolourise bromine water, due to the 3 double bonds

Question 5

evidence for the delocalised model (enthalpy of hydrogenation)

Answer 5

hydrogenation of cyclohexane with 1 C=C has and enthalpy change of -120 kjmol-1. if benzene had 3 C=C bonds it should have a enthalpy change of -360 kjmol-1 (the kekulé model)
the actual enthalpy change is -208 kjmol-1

Question 6

how to name aromatic compounds

Answer 6

using a benzene suffix.
when there is another functional group e.g. -OH or -NH2, there is a phenyl prefix. e.g. phenol and phenylamine

Question 7

why is benzene a stable molecule

Answer 7

the electron ring gives the molecule stability due to the overlap of the electron cloud.