Chapter 25 - Aromatic compounds Flashcards
What is the molecular formula of benzene?
C6H6
What is the Kekulé model?
Carbon atoms joined together with alternating double and single bonds
What are the three pieces of evidence that disproves the kekulé model?
Benzene does not take place in electrophilic addition reactions which alkenes do, all the bond lengths are between the length of single and double bonds and the enthalpy change of hydration of benzene is less negative than three double bonds.
Describe the structure of benzene?
Each carbon atom has a delocalised electron in a p orbital forming a ring of electron density and a system of pi-bonds
What groups are prefixes to benzene?
alkyl groups, halogens and nitro groups
When is the prefix phenyl used when naming benzene?
When the benzene ring is attached to an alkyl chain with a functional group or contains seven or more carbons
What does benzene and nitric acid form?
nitrobenzene
What catalyst and heat is used in forming nitrobenzene?
sulphuric acid at 50 degrees celsius
what type of reaction mechanism is the nitration of benzene?
electrophilic substitution
what happens if the temperature in the reaction between nitric acid and benzene is heated above 50°C?
further substitution reactions may occur leading to the production of dinitrobenzene
what is the electrophile in the nitration of benzene?
a nitronium ion
what is needed for the halogens react with benzene?
A halogen carrier
what is the reaction mechanism for the reaction between benzene and halogens?
electrophilic substitution
what would happen during bromination of the benzene ring?
One of the hydrogen atoms on the benzene ring is replaced by bromine atom
what is the alkylation of benzene?
The substitution of hydrogen atom in the benzene ring by an alkyl group
what is formed when benzene reacts with an acyl chloride in the presence of a aluminium chloride catalyst?
an aromatic ketone
what is the reaction mechanism for when alkenes decolourise bromine?
electrophilic addition
why does benzene not react with bromine unless a halogen carrier catalyst is present unlike alkenes?
when a nonpolar molecule approaches the benzene ring there is insufficient electron density around any two carbon atoms to polarise the bromine molecule
what are phenols?
A type of organic chemical containing a hydroxyl functional group
why is phenol less soluble in water than alcohols?
due to the presence of the nonpolar benzene ring
what happens to phenol in water?
it partially dissociates forming the phenoxide ion and a proton
how do we know that phenol is more acidic than alcohols but less acidic than carboxylic acids?
ethanol does not react with strong or weak bases, phenol and carboxylic acids react with strong bases but only carboxylic acids can react with weak bases
A reaction with what can be used to distinguish between a phenol and a carboxylic acid
Sodium carbonate
Phenol reacts with sodium hydroxide to form what products and what kind of reaction
Salt, sodium phenoxide and water in a neutralisation reaction
The bromination of phenol and the nitration of phenol examples of what kind of reaction
Electrophilic substitution
why does bromine and nitric acid react more readily with phenol than they do with benzene?
The lone power of electrons from the oxygen of the OH group are donated into the pi system of phenol so the electron density of the benzene ring in phenol is increased which attracts electrophiles more strongly
what is the name of a second substitution?
Disubstitution
what does bromine require to react with benzene?
A halogen carrier
does bromine require a hydrogen carrier to react with phenylamine?
No, it reacts rapidly
why does nitrobenzene react slowly with bromine and requires a hydrogen carrier and a high temperature?
The benzene ring in nitrobenzene is less susceptible to electrophilic substitution than benzene itself
what does the NH2 group do to the ring as a result of the aromatic ring reacting more readily with electro files?
It activates it
What does the N2 group do to the aromatic ring as the ring reacts less readily with electrophiles?
It deactivates it
What positions does the NH2 group direct the second substituent?
two and four
what position does the NO2 group direct the second substituent?
three
what position does the OH group direct the second substituent?
Two and four
are two and four directing groups activating or deactivating groups?
Activating
what group of elements are two and four directing groups but not activating groups?
The halogens
Are three directing groups deactivating or activating?
Deactivating
