Flashcards in Aromatics Deck (18):
What hybridisation is present in aromatics?
How many sigma bonds and pi bonds does a benzene ring have?
12 sigma, 1 pi
Why does benzene tend to undergo substitution reactions as opposed to addition?
Addition reactions disrupt the delocalisation and so reduce the stability of the ring. Substitution reactions result in no disruption to the stability of the ring and so the stability is maintained.
What do the delocalised electrons in the pi molecular orbital make the benzene susceptible to attack by?
Name 4 electrophiles and the products they produce.
Alkylation (CH3+) - Methyl benzene
Chlorination (Cl+) - Chlorobenzene
Sulphonation (HOSO2+) Benzenesulphonic acid
Nitration (NH2+) Nitrobenzene
How are Cl + ions are made?
Cl + ions are made when chlorine is used as the reagent with aluminium chloride
How is the nitronium ion created?
The reaction between concentrated nitric and sulphuric acids.
How is the HOSO2+ electrophile generated?
Generated from concentrated sulphuric acid.
What electrophile is generated from concentrated sulphuric acid with sulphur trioxide added?
SO3H (Sulphur carries a partial positive charge)
What type of chemical is phenol?
A weak acid
Why is the phenoxide ion so stable?
An electron in the p orbital in the oxygen atom becomes part of the pi molecular orbital of the benzene ring. Electron delocalisation therefore extends over the whole ion and so increases its stability.
What will phenols form when reacted with alkalis?
What is phenyl amine?
It is an aromatic primary amine
What type of molecule is phenyl amine?
A weak base, which partially ionises in solution
What happens to the lone pair of electrons when phenyl amine is in water?
They accept a proton from water, forming the phenyl ammonium ion and the hydroxide ion.
What does the degree of weakness of an amine depend on?
How ready the lone pair of electrons on the nitrogen atom is to accept a proton.
Why is the phenyl amine molecule more stable then the phenyl ammonium ion?
Because the pi molecular orbital takes up the lone pair of electrons on the phenyl amine group, electron delocalisation is extended into the ammonium group. In phenyl ammonium no extension of electron delocalisation can take place.