aromatic chemistry Flashcards
what is aromatic chemistry
the study of benzene and compounds containing the benzene ring
what are compounds containing the benzene ring called
arenes
evidence against the kekule structure of benzene
- benzene doesn’t decolourise bromine water (whereas c=c does)
- carbon carbon bond lengths (C=c shorter than C-C)
- thermochemical data for the hydrogenation of benzene suggests that more stable than the kekule structure
justfifcation for c-c bond lengths in benzene
bond lengths intermediate- benzene is a regular hexagon- if bonds single double alternating would be irregular
how does thermochemical data for hydrogenation of benzne suggest its more stable than expected
enthalpy is roughly 150kJ/mol more stable than expected
what structure does benzene have
a regular, planar, hexagon structure
why does benzene have a regular planar hexagon structure
the six c atoms and the six h atoms are all in the same plane
what are all bond angles in benzene
120 degrees
how are the 6 c-c bond intermediate in length
between length of a c-c and a c=c bond
how does the pi bond form
overlap of adjacent p orbitals
where does the pi bond form
above and below the ring
what is the pi bond essentially
an electron cloud above and below the ring
where are elections In the pi bond
delocalised
why are the pi bonds in benzene harder to break than a normal c=c bond
the delocalised structure has extra stability
which part of the benzene ring attracts electrophile
the pi bond above and below the plane
is an area of moderately high electron density
electrophile
an electron pair acceptor
what happens in the electrophilic substitution reaction of benzene
a h atom from the benzene ring is replaced by a new group of atoms
why does benzene undergo substitution rather than addition
to preserve the stability of the delocalised pi bond
nitration:reagents
conc sulphuric and conc nitric
sulphuric is catalyst
nitration: conditions
below 50 degrees Celsius
nitration: overall equation
benzene+ nitric > nitrobenzene + water
nitration: electrophile
nitronium ion NO2+
nitration: generation of electrophile equation
H2SO4 + HNO3 > NO2+ + HSO4- + H2O
nitration: regeneration of catalyst
H+ + HSO4- > H2SO4
acylation: reagents
acyl chloride
acylation: conditions
AlCl3 (halogen carrier) and heat
acylation: general equation
benzene + acyl chloride > (benzene)-COR + HCl
acylation: electrophile
RCO +
acylation: benzene + ethanoyl chloride
generation of electrophile
CH3COCl + AlCl3 > CH3CO+ + AlCl4-
acylation: benzene + ethanoyl chloride
regeneration of catalyst
AlCl4- + H+ > AlCl3 + HCl
reaction mechanism cyclohexene and bromine
electrophilic addition
reaction mechanisms benzene and bromine
electrophilic substitution
why are the reactions different: benzene
- delocalised pi bonds
- lower electron density
- need to generate Br+ for the reaction to occur
why are the reactions different: cyclohexene
- localised pi bonds
- greater electron density
- able to induce dipole in Br2
why is methyl benzene more reactive than benzene with electrophiles
- CH3, through positive inductive effect, provides more electron density
- increases electron density of delocalised pi bond
- methyl benzene better at attracting electrophiles
why is the nitration of benzene an important reaction
nitrogen containing aromatic compounds have many applications
uses of nitrobenzene
explosives
reagents for nitration of benzene
conc nitric and conc sulphuric
uses of benzene with -NH2 group attached (amine)
dyes and drugs
how to get from nitrobenzene to benzene with an -NH2 group (amine)
conc hydrochloric
tin catalyst
what can nitrobenzene be reduced to form
amine
equation for reduction of aromatic nitro compounds
benzene-NO2 + 6[H] > benzene-NH2 + 2H2O
