ORGANIC CHEMISTRY - aromatic chemistry Flashcards
what is benzenes formula and structure?
C6H6
what is another name for arenes? why is it named this?
aromatic compounds as it was first found in sweet smelling dyes
what is the most common type of reaction for benzene?
substitution of H for a different functional group
what is the shape of benzene?
flat
hexagon
bond angle - 120 degrees
what is the bond length between adjacent C-C atoms on benzene?
0.139 nm
What happens to the fourth electron in the P orbital of each carbon atom in benzene?
It delocalises to form rings of electron density above and below the hexagon, forming rings of delocalised electron density above/below hexagon.
what is the effect on benzene’s stability of the rings of electron density?
makes benzene very stable, even though it is unsaturated
what is the thermochemical evidence that benzene is more stable than kekules structure?
- hydrogenation of cyclohexene = -120kJmol
- kekules structure = -360
- benzene hydrogenation = -208kJmol so benzene is 152kJmole more stable
why else is kekules structure not suitable for benzene?
- kekules structure would not be symmetrical as the C=C double bond is shorter than the single bond.
- kekule structure would easily undergo addition reactions across the double bond however benzene does not.
- would form two isomers on the addition of a bromine - benzene does not
what is the appearance of benzene at 298K?
colourless liquid
why does benzene have a relatively high melting point?
close packing of flat hexagonal molecule when solid
is benzene soluble in water?
no as it is non polar
dangers of benzene
it is a carcinogen
how do you name compounds containing a benzene ring?
- benzene or phenyl
why is benzene attacked by electrophiles?
high electron density above and below ring due to delocalised electrons
What is delocalisation energy and what is the effect of this on benzenes reactions?
Large amount of energy needed to break aromatic ring apart. Results in the aromatic ring almost always stay intact.
What is seen when benzene is combusted?
smoky flames from unburnt carbon due to high C:H ratio
draw general electrophilic substitution mechanism on benzene.
diagram
Which iron is used to nitrate benzene?
NO2+/ NITRONIUM ION
How is nitronium ion generated?
- conc H2SO4 and conc HNO3
H2SO4 + HNO3 —-> HSO−4 + [NO 2] + + H 2O
how is H2SO4 catalyst regenerated in the nitration of Benzene?
HSO4- + H+ –> H2SO4 ( H+ from benzene ring)
draw mechanism and overall equation for the nitration of benzene?
draw and write
What are the uses of nitrated arenes?
Production of explosives e.g. TNT
To make aromatic Amines that are used for industrial dies
How do substituents with a positive inductive effect (eg alkyl groups) affect further substitution?
they release electrons into the delocalised electron ring, increasing the electron density and making further substitution reactions more likely.
