Aromatic Compounds - organic Flashcards
(24 cards)
structure of benzene
- C6H6 - planar cyclic stu
- carbon bonded to either side and one hydrogen
-unnpaired electron of each carbon in p orbital stick out above and below the plane
all bond length equal
Stability of benzene reason
- enthalphy of hydrogenation of benzene and clycohexane compare - in theory should be same
- but benzene’s lower - less exo than expected - requireds more energy to break bond and distrupt pie system - more endo
( which is more endo )
Stability of benzene - how
delocalised ring shared over more atoms
- eng of the molecule = lowered
more stable
Naming aromatic compounds
- suffix = benzene
- pfefix = phenyl
electrophilic substitution
- electronphile - electron acceptor
- benzene - no ele addition but insted substitution ( addition would destroy delocalised rings of electron)
Nitration
- condition = warm benzene, conc sulphuric and nitric acid
1. making electrophile = H2So4+HNO3 = HSO4- +H2NO3+
H2NO3+ = H2O + No2+
2. electrophilic subs
3. reforming catalyst =
HSO4- + H+ = H2SO4
Uses of nitration
- dye, pharmaceuticals
- react violently when heated, used as explosives ( TNT )
Friedel crafts acylation
- add actyl group to benzene ( RCOCl )
- produce = HCl and Phenyketone
- condition - heated under reflux in non - aqueous solvent
Acyl group - not strong electrophile
how to make weak electrophile strong
- needs to be strong to attack benzene
- made stronger using catalyst = halogen carriers (AlCl3)
- AlCl3 = lone pair acceptor
- as lone pair of electrons pulled away the polarisation in acyl chloride inc - froms CC
(- Cl from RCOCL ( Acyl chloride ) , attack the AL - CL leave acyl chloride
Carbon cation generated - more stronger electrophile )
Pg : 451
https://www.chemguide.co.uk/mechanisms/elsub/halogenation.html
What are amines
Ammonia + organic group ( alkyl, aromatic compound)
- just replace on hydrogen = primary , 2 sec, 3 tertiary,4 = quaternary ammonium ion
Because ammoniu, quaternary ions is positive = near neg ions
- the complex = quaternary ammonium salt
Naming amines
- suffix = amide
-Prefix = alkyl ( methanamide )
2 org group =di, 3 = tri , 4 = tetra
Cationic surfactants
- Compounds partly soluble, partly insoluble ( polar / non polar )
- these compounds = quaternary ammonium salts with at least one hydrocarbon chain
Hydrocarbon = bind to non polar substance
Polar head = attaches to polar molecule = water
Amines as bases
- weak base =proton acceptor
- nitrogen atom fromd co-ordinatye bond
Strength depends on the availability of lone pair from nitrogen - primary aromatic amine = benzene ring pulls the lone pair toward its,ef - less available
- primary aromatic amine = alkyl group pushes line pair away from nitrogen- more available - strongest base
- ammonia = in the middle
Amides
Derivative of carboxyl group ( CONH2)
- carboxyl pulls electron away from NH2
Suffix = amide , prefix = acyl group
N substituted amides
- amides where one hydrogen attached to nitrogen has been substituted with alkyl group
Naming = N ( alkyl group) amide
Molecule = ethanamide, one hydrogen attached to nitrogen substituted with methyl group Naming
N-methylethanamide
Formation of amines
- nucleophilic substitution of halogenoalkene
- formation of amine from nitriles
Formation of amine by halogenoalkenes
Condition : amines made by heating halogenoalkene with excess ethanoic ammonia
- will get mixture of amines = primary, secondary, tertiary and only stop when quaternary ammonium salt has been formed ( more than one hydrogen likely to be substituted )
Ammonia = attack the CC
NH2 attack hydrogen
Formation by nitriles
Can reduce nitriles to amine using strong reducing agent ( lithium aluminium hydride) LiAlH4 and dilute acid
- LiAlH4 = expensive so industry use metal catalyst- platinum or nickel at high temperature ( catalytic hydrogenation
Amines as nucleophiles unfinished
- acyl chloride & reacts with ammonia to from primary amide
- acyl chloride and primary amide to form nucleophilic addition elimination
Formation of aromatic amines
- produced by reducing nitro compound
1 mixture of nitro compound, tin metal and concentrated HCl heated under reflux - salt formed
2 turn salt to aromatic amines - need to make it alkali- add NaOH
structure of clycohexene
- each carbon has 4 covalent bond
- 4 of the 6 carbon attempt to have a tetrahedral shape with bond angle of 109.5
- 2 of the 6 carbon from a pi bond
- 2 of the 6 carbon attempt to have a trigonal planar shape with bond angl of 120
- there ismixture of C-C and C=C bond lengths
poly(propene)
- does not have delocalised electron
- all the electrons are involved i the covalent bonding of the molecule
conversion of benzene into clycohexane
- C6H6 + 3H2 = C6H12
- Nickel / platinum catalyst
describe difference in orbital overlap between benzene and (kekule model) benzene
- both have overlap of p orbital to form pi bonds
- in benzene pi bonds are delocalised
- in bensene ( kekule model ) pi bonds are localised between =2 carbon atom
