Benzene Flahcards Flashcards
Nitration of benzene
Electrophile substitution
HNO3 + H2SO4 -> HSO4- + NO2 + H2O
H+ + HSO4- -> H2SO4
50°c
Halogenation of Benzene
Halogen carrier + halogen -> FeCl4- + Cl+
Electrophile substitution
Halogen+ ion is electrophile
FeCl4- + H+ -> FeCl3 + HCl
Structure of benzene
Each of 6C atom is bonded to two other and one H atom.
A p orbital from each c atom with one electron in form pi bonds above and below plane of carbon atoms to form clouds of high electron density
The electrons are delocalised
Kekule
Enthalpy change of halogenation is not what is expected
Bond length is between c-c and c=c
Dose not recolour use bromine water under normal conditions
Properties of benzene
Colourless liquid
Sweet odour
Highly flammable
Carcinogen ( anaemia, leukaemia)
Where is benzene found
Volcanoes
Forest fires
Crude oil, petrol, cigarette smoke
Properties of phenol
Solid at room temp + pressure
Slightly soluble
Weak acid
Takes part in acid reactions
Increased reactivity of phenol
A lone pair of electrons from oxygen overlaps with the ring and the electrons become delocalised as well
Higher electron density
Polarises bromine so attracted more strongly to the ring structure
Uses of phenols
Detergents
Antiseptic
Preparation of pharmaceuticals
Epoxy resins.
Why does the carbonyl group not react the same as an alkene
The oxygen atom is more electronegative
So the electrons are attracted more to the oxygen creating a dipole
Reducing aldehydes and ketones
Nucleophilic addition
Sodium tetrahydridoborate (III) generates hydride ions
Electron deficient carbon attacked by nucleophile
Pi bond breaks electrons to O
Negatively charges intermediate
Intermediate donates electron pair to hydrogen on water
Hydroxide formed
Detecting carbonyl in ketone and aldehydes using Brady’s reagent
Add 2,4-DNP methanol and H2SO4
If aldehyde or ketone an orange/yellow precipitate of 2,4-Dintirophenylhydazone
Using Tollens’
NaOH+ AgNO3 Silver oxide brown precipitate Dissolve in dilute aqueous ammonia Aldehydes silver solid Ketone no reaction / not oxidised
How to identify a carbonyl compound
2,4-dinitrohydrazone is impure so filter Recrystallise Filter again Melting point is measured And compared to table
Base properties in amines with alkyl groups
Alkyl groups are slightly electron donating
Called inductive effect the more alkyl chains the more basic