6.1.6: Electrophilic substitution in aromatic compounds Flashcards
What is the directing effect?
How a functional group attached directly to an aromatic ring affects which carbon atoms are more likely to undergo substitution.
Phenol will readily undergo electrophilic substitution with a variety of reagents without a catalyst. What is this enhances reactivity due to?
Extra electrons from the oxygen on the hydroxyl group being donated to the pi-system of the aromatic ring.
What happens when phenol reacts with bromine?
- A triple substitution reaction.
- A white precipitate of 2,4,6-tribromophenol forms
What conditions are required for the bromination of phenol and what is the balanced symbol equation.
C6H5OH + 3Br2 —> C6H2Br3OH + 3HBr
What happens when phenol is reacted with dilute nitric acid?
What are the conditions required and what is the balanced symbol equation?
- The reaction forms a mixture of 2-nitrophenol and 4-nitrophenol.
- Room temperature.
- C6H5OH + HNO3 —> C6H5(NO2)OH + H2O
What happens when phenol is reacted with concentrated nitric acid?
A triple substitution reaction occurs forming 2,4,6-trinitrophenol.
What is the 2- and 4-directing effect?
- In phenol, the hydroxyl group pushes the additional electrons into the pi-system. This makes substitution reactions mainly occur on the 2 and 4 positions of the aromatic ring.
- The hydroxyl group activates these carbon atoms so their rate of substitution is faster than the other positions.
when is the 2- and 4-directing effect more pronounced?
When an NH2 group is directly attached to the aromatic ring.
What directing effect is observed when an -NO2 group is directly attached to the aromatic ring?
A 3-directing effect can be seen as the nitro group withdraws electrons from the pi-system and makes the rate of substitution highest on the third carbon atom.
Why is considering electron donating and withdrawing effects important to consider in in organic synthesis?
Because it is important that a reaction pathway can be designed to maximise the desired product. considering electron donating and withdrawing effects of a directly attached functional group allows you to make predictions on the positions in which substitutions will take place.
