Benzene
What are examples of activating groups?
-NH2 -OH -R -halogens
What is the evidence against kekules structure?
1. *lack of reactivity* If benzene contained the double bonds as suggested, when mixed with bromine water it should decolourise however benzene will not undergo any electrophilic addition reactions 2. The bonds are all the same length in benzene, there are *no single length and double length bonds* and the bonds in benzene are somewhere between the single and double 3. less energy is produced than expected from the hydrogenation of benzene, meaning that its *enthalpy does not match the 3single and 3 double*
How do you name aromatic compounds?
> alkyl and nitro groups are all prefixes > when benzene is attached to an alkyl group with a functional group, benzene also becomes a functional group (phenyl)
How is benzene acylnated?
> benzene reacts with an acyl chloride in the presence of a halogen carrier > electrophilic substitution
How does benzene react with nitric acid?
> catalysed by sulfuric acid at 50 degrees > one of the hydrogen atoms is replaced by a nitro group -NO2 > electrophilic substitution > the electrophile is (NO2)+ HNO3 + H2SO4 --> (HSO4)- + NO2+ + H2O > in the second step, the benzene ring +NO2 accepts a pair of electrons from the benzene ring to form a covalent bond
How does phenols acidity compare to carboxylic and alcohols?
> ethanol does not react with NaOH (strong base) or sodium carbonate (weak base) > phenols and carboxylics react with solutions of strong bases (NaOH) > carboxylics react with weak bases
How is benzene alkynated?
> reacting benzene with a halogen carrier and a haloalkane > increases the number of carbons > produces HCl
How does benzene react with halogens?
> will only react with a halogen carrier present (AlCl3, FeCl3..) > room temp and pressure > electrophilic substitution > benzene is too stable to react with a non polar bromine molecule so a Br+ needs to be generated from the halogen carrier > bromonium ion accepts a pair of electrons from the benzene ring to form dative covalent bond > breaks down as is unstable to form bromobenzene and a H+
What is benzene?
A hexagonal ring of 6C atoms classified as an arene > flammable, sweet smelling and colourless classified as a carcinogen
What is phenol?
A type of aromatic compound with a hydroxyl group attached directly to the carbon ring
How does the reactivity of benzene compare with alkenes?
Alkenes decolourise bromine by electrophilic addition whilst benzene will only react if a halogen carrier is also present > the electron density around two carbons is less than a double bond and is not enough to polarise a bromine
How does phenol react with nitric acid?
Can form either 2-nitrophenol or 4-nitrophenol
How are phenol and benzene different in terms of reactivity?
Increased reactivity of phenol comes from the lone pair of electrons on the oxygen in the hydroxyl group that is donated to the pi-system > electron density of the benzene ring in phenol is then increased so attracts more electrophiles more strongly than benzene > aromatic ring is therefor more susceptible to attack from electrophiles
What is the delocalised model of benzene?
Is a planar hexagonal six carbon ring where each carbon uses three of its electrons to bond to adjacent carbons and a hydrogen atom > the last electron is in the p-orbital which overlaps to adjacent p-orbitals above and below the plane > forms a ring of electron density *(delocalised pi ring)*
How does phenol react with NaOH?
It is a neutralilsation reaction where a salt (phenoxide) and water is formed
What is activation and deactivation?
NH2 (amine) reacts readily with benzene because it is an activating group so directs the second substitution to the 2, 4 position whilst NO2 (nitro) is a deactivating group so does not react as readily and directs to the 1, 3, 5 position
How does phenol act as a weak acid?
Phenol is less soluble in water than alcohols due to the benzene ring > when dissolved in water, in produces a phenoxide ion and a proton > because is can partially dissociate, it can be classified as acidic
What are example of deactivating groups?
RCOR -COOR -SO3H -CHO -COOH -CN -NO2 -NR3-
How does phenol react with bromine?
Reacts with aqueous bromine to form a white precipitate and decolourises the bromine water from orange to colourless > halogen carrier not required > room temp and pressure
What is kekules structrue?
Suggested a structure based on a six carbon ring with alternating single and double bonds
