6.1.1 Aromatic Compounds

What are the two major classes of organic chemicals?

• aliphatic

• aromatic or arene

Define aliphatic

straight or branched chain organic substances

Define aromatic/arene

includes one or more ring of six carbon atoms with delocalised bonding.

which class does Benzene belong in

Benzene belongs to the aromatic class.

what is the simplest arene called?

benzene

Describe Benzene’s structure

• 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

In 1865 what did Kekule suggest

he suggested a structure for Benzene consisting of alternate single and double covalent bonds between the carbon atoms

was Kekule (1865) correct about the structure and state your reasoning

• The structure is not correct.

• Evidence suggests that all the C-C bonds are the same length.

In formula for benzene why do we draw a circle?

to show this delocalised system

The six electrons in the pi bonds of the benzene are […] and […] over the whole ring

The six electrons in the pi bonds of the benzene are delocalised and spread out over the whole ring

what does delocalised mean in the context of structure of Benzene?

Delocalised means not attached to a particular atom.

what type of molecule is Benzene?

Benzene is a planar molecule

In Benzene, evidence suggests all the C-C bonds are […] and have a length and bond energy between a […]

In Benzene, 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

what is H-C-C bond angle in Benzene

120 degrees