Aromatic Chemistry (Arenes) Flashcards
(17 cards)
Why was the bonding and structure of benzene a puzzle for a long time?
- Even though being unsaturated, it did not readily undergo addition reactions.
- All the C atoms were equivalent, implying all C-C bonds were the same.
What does benzene consists of?
Flat, regular hexagon of C atoms, each of which is bonded to a single H atom.
What is delocalisation?
Electrons are spread over more than two atoms.
What is the delocalisation like in benzene?
There are 6 delocalised p orbital electrons. So the p orbitals overlap and a ring of high electron density above and below the ring.
What is known as the stability of benzene?
Aromatic stability
What are the physical properties of benzene?
- Colourless
- Liquid at room temp
- High melting point as hexagonal molecules pack well together in the solid state
- Do not mix with water but mix with other hydrocarbons and non-polar substances
Give the two important factors to the reactivity of aromatic compounds.
- Ring is an area of high electron density so is attacked by electrophiles.
- Ring is very stable, so requires the delocalisation energy for the system to be destroyed.
What reactions do aromatic systems undergo?
Electrophilic substitution
How do arenes burn in air?
Smoky flames due to the high C:H ratio. Usually unburnt C remaining when they burn in air which produces soot.
What does a smoky flame suggest?
an aromatic compound
Why do aromatic compounds not undergo electrophilic addition reactions?
Requires the input of the delocalisation energy to destroy the aromatic system.
What is nitration?
Substitution of an NO2 for a H.
What is the electrophile in nitration?
NO2+
What is required to produce the electrophile in nitration?
Conc. HNO3 and Conc. H2SO4
What are the uses of nitrated arenes?
Important step in the production of explosives like TNT. First step in making aromatic amines which are then used to make industrial dyes.
What is the catalyst for Friedel-Crafts reactions?
AlCl3
What is acylation a useful step in the synthesis of?
New substituted aromatic compounds.
