UNIT 3 Section 6 - Aromatic compounds and Amines Flashcards
what electron system does benzene have
delocalised electron ring
what is the formula for benzene
C6H6
what are the problems with Kerkules structure
- carbon carbon bonds are all the same length in the structure but we know double bonds are shorter
- benzene does not undergo addition reactions easily even though the structure has double bonds present
- we don’t get the expected isomers when we react benzene
- the hydrogenation of benzene is 152kjmol-1 less than expected if the structure was correct
why does benzene not undergo addition reaction easily
the delocalised electron ring is very stable and by removing these electrons to make another bond you make a less stable product
what is the expected enthalpy of hydrogenation of cyclohexatriene and how do you know
-360 as it is 3x -120 and -120 is the enthalpy of hydrogenation of one double bond in cyclohexatriene
why do we know benzene is more stable than cyclohexatriene
it requires more energy to hydrogenate benzene and therefore we know it requires more energy to break the delocalised system of electrons as less energy is given out when you break the bonds
why is cyclohexatriene so stable
it has alternating double and single bonds causing delocalised electrons which can overlap in the p orbitals meaning the electrons can move between them and this partial delocalisation causes stability in a compound
what type of reaction is nitration of benzene
nitration
what are the reactants needed in nitration of benzene
concentrated H2SO4 and HNO3
what is the mechanisms of nitration of benzene
electrophilic substitution
what are the equation to make the electrophile needed in the nitration of benzene
- HNO3 + H2SO4 –> H2N+O3 + HSO4-
- H2N+O3 —–> H2O + +NO2
what is the overall equation in forming the electrophile needed for nitration of benzene
HNO3 + H2SO4 —-> +NO2+ H2O + HSO-4
what is an amine
a lone pair on a nitrogen with 3 single bonds
what is the intermolecular bonding like between amines
hydrogen bonding between 1 and 2 amines
tertiary amines have dipole- dipole
what is an aromatic amine
when you have a N joined to a benzene ring with a lone pair
what is a cationic surfactant
quaternary ammonium salts with at least one long hydrocarbon tail which are partly soluble and insoluble in water
what are uses of cationic surfactants
fabric softeners and hair products
how do we measure the strength of a base
by how well it accepts protons
what does a high electron density mean for a base
the higher the electron density of a lone pair the stronger the base will be
what is a weaker base ammonia or ethylamine and why
Ammonia is a weaker base as there are no electron donating groups to cause the positive inductive effect whereas ethylamine has a positive inductive effect as the alkyl groups donate electron density to the N and its lone pair to become more available for protons
what is a weaker base ammonia or phenylamine and why
phenylamine is a weaker base as it has a benzene ring that causes the nitrogen’s lone pair to become partially delocalised in the ring and is therefore less available to form a dative bond with a H+
if the conditions for nucleophilic substitution of amines and halogenoalkanes is excess ammonia what is the main product
primary amines
if the conditions for nucleophilic substitution of amines and halogenoalkanes is excess halogenoalkane what is the main product
quaternary salts
can ammonia act as an electrophile to benzene and explain why
no as the delocalised ring in benzene repel the lone pair on the N
what are uses of aromatic amines
explosives and dyes
what are the three ways to make amines
- React nitrobenzene with a reducing agent under reflux with tin and conc. HCL followed by NaOH
- Reacting a nitrile with a reducing agent with LiAlH4 followed by dilute HCL
- nucleophillic substitution by heating a halogenoalkane with excess ethanolic ammonia
