Arenes - Physical properties, naming and reactivity
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Physical state and colour of benzene at room tempertaure?
Colourless liquid at room temperature
Compare the boiling and melting points of benzene and hexane (bp - similar, mp - b>h)
Their boiling points are very similar, whereas the melting point of benzene is much higher than hexane
Why does benzene have a higher melting point than hexane? (B. = flat + hex. - pack tgthr - sol. state)
Benzene molecules are flat and hexagonal, so they pack together efficiently in the solid state
How does efficient packing affect benzene’s melting point? (energy> - sep mols. - inc m.p.)
More energy is needed to separate the molecules, increasing the melting point
Are arenes insoluble? Why, yes/no.
No, because arenes are non - polar, whilst water is polar
What solvents do arenes dissolve in?
Other hydrocarbons and non - polar solvents
What two factors control the reactivity of aromatic compounds? • elec. dens. • stab. ring
• High electron density in the ring • High stability of aromatic ring
What type of species attacks the benzene rings
Electrophiles
What is delocalisation energy, and what affect does it have on benzene reactions? (energy - break delo. ring sys. - ring intact - most reac.)
The energy required to break the delocalised ring system, meaning the ring almost always remains intact during reactions
What type of reactions do arenes mainly undergo?
Electrophilic substitution reactions
Why do arenes undergo substitution rather than addition?
Substitution preserves the delocalised ring system
AQA exam phrasing that links reactivity and structure? (b. ring - high e- dens. - stab. by deco. engy. - undergoes elec. subs.)
The benzene ring has high electron density but is stabilised by delocalisation energy, so it undergoes electrophilic substitution
What forms the root name of aromatic compounds?
Benzene
When benzene is bonded to an alkyl chain with a functional group, how do you name the benzene ?
The benzene becomes a side chain, so the suffix is used “phenyl”
Name and draw C6H5C2H5
Name: ethylbenzene
Name and draw C6H5NO2
Name: nitrobenzene
Name and draw C6H4(CH3)2
Name: 1,2 - dimethylbenzene