Arenes - physical properties, naming and reactivity

Question 1

How does the boiling and melting points of benzene compare the hexane?

Answer 1

benzene is a colourless liquid at room temperature

there is a 1 K difference in the boiling point of hexane (354 K) and benzene (353 K)

but its melting point (279 K) is much higher than hexanes (178 K)

Question 2

What causes the difference in melting point?

Answer 2

benzene’s flat, hexagonal molecules pack together very well in the solid state and are therefore harder to separate

this must happen for the solid to melt

Question 3

How are substituted arenes given a name?

Answer 3

named as derivatives of benzens

so benzene forms the root of the name

e.g. methylbenzene, C6H5CH3

Question 4

What happens if there is more than one subsituent? How is it named?

Answer 4

the ring is numbered

the first substituent in always given the number 1

e.g. 1,2-dimethylbenzene - C6H4(CH3)2

Question 5

How does the ring of delecolalised bonding affect the reactivity?

Answer 5

the ring is an area of high electron density

therefore it is attacked by electrophiles

Question 6

How does the ring almost always remain intact?

Answer 6

the aromatic ring is very stable

it needs energy to be put in to break the ring before the system can be destroyed

this is called the delocalisation energy

Question 7

How do arenes mostly react?

Answer 7

electrophillic substitution