1. 14 – Aromatic Hydrocarbons
Organic Chemistry
14 – Aromatic Hydrocarbons
Leaving Certificate Chemistry

2. An aromatic compound is a compound containing a benzene ring
Originally such compounds were called ‘aromatic’ as they had nice smells
Benzene: C6H6

3. Derived from whale oil – 1825 – Michael Faraday
Benzene: C6H6
Derived from whale oil – 1825 – Michael Faraday

4. By 1834: Molecular formula known to be C6H6
Benzene: C6H6
By 1834: Molecular formula known to be C6H6
Chemical formula suggests a highly unsaturated compound
But Benzene does not decolourise bromine water OR acidified potassium permanganate
Benzene undergoes substitution reactions rather than addition.
Confusion

5. H H C C H H H H C C C C C C C C H H H H C C H H Benzene: C6H6
What is the chemical structure of benzene? H H C C H H H H C C C C C C C C H H H H C C H H

6. 1 picometre is one trillionth of a metre
Benzene: C6H6
Bond Lengths C C
154 picometres C C
134 picometres
But all of the bond lengths in Benzene are of the same length of 140 picometres
One very big problem
1 picometre is one trillionth of a metre

7. Benzene: C6H6 H C H H C C C C H H C H Benzene: C6H6
He suggested that six electrons revolve around the entire six carbon atoms and this explains why all carbon-carbon bond lengths are equal
2007 Q. 4(i) (6) C H H C C C C H H C
Structure revealed by Kekule in 1865
Benzene: C6H6 H

8. Methylbenzene
CH3
Methylbenzene is preferable for use over benzene in a laboratory as benzene is carcinogenic
2006 Q. 4 (d) (6)
Used as an industrial solvent
Also called toluene
Methylbenzene: C7H8

9. Ethylbenzene
C2H5
2005 Q. 4(g) (6)
Ethylbenzene: C8H10

10. Physical properties of benzene?
Physical state: Benzene, Methylbenzene and ethylbenzene are liquid at room temperature
Insoluble in water
Soluble in non-polar solvents such as cyclohexane