Topic 18 Organic III Flashcards
What did Kekule suggest the benzene structure to look like?
Cyclohexa1,3,5-triene
How was Kekule’s benzene structure suggestion proved/disproved?
Supported by
- very sooty after combusting (due to low C:H ratio)
Disproved by
- bromine water does not react, so no C=C bonds
- regular bond lengths
- enthalpy of hydration values
What are chemical evidences for the structure of benzene?
- Bromine water doesn’t decolourise, so no C=C present
- X-ray crystallography, equal bond lengths so same bonds between each C
- Enthalpy of hydration data - much lower than expected
What do you see with HCl / HBr/ HI?
WHITE MISTY FUMES
benzene + O2 →
(complete)
6CO2 + 3H2O
benzene + O2 →
(incomplete)
3H2O + 6C
or
6CO + 3H2O
depending on Q - always 2 products
benzene + bromine with catalyst →
catalyst FeBr3
bromobenzene + HBr
what are the 4 stages of electrophilic substitution?
- formation of electrophile
- attack of electrophile
- reformation of π system
- reformation of catalyst
benzene + conc nitric acid + catalyst →
catalyst conc H2SO4
nitrobenzene + H2O
benzene + halogenoalkanes + catalyst →
What conditions?
catalyst AlCl3
alkyl benzene (or phenyl alkane) + HX
in reflux
benzene + acyl chloride + catalyst →
catalyst AlCl3
phenyl ketone + HCl
what are methyl benzene’s properties?
alkyl group is e- pushing
so pushes e- density into pi system
so more easily attacked by electrophiles
what’s another name for methyl benzene?
toluene
is benzene or methyl benzene more reactive?
methyl benzene
has lower activation energy
e- pushing, higher e- density in ring, so more susceptible to attack by electrophiles
what is a phenol?
benzene with OH attached to one of the C
phenol + bromine/bromine water →
What are the products and what is observed?
2,4,6-tribromophenol + 3HBr
white ppt
no heating, no catalyst
phenol + dil HNO3 →
mixture of 2-nitrophenol and 4-nitrophenol
pH of phenol?
weak acid
reacts like alcohol
but more stable
due to resonance stability (feeing e- into delocalised pi system)
what is the amine functional group?
N with lone pair
What is the amide functional group?
-C=O
|
N
How to identify amino acids?
Most have chiral C
Has amino group
and COOH group
Butyl amine + water →
Butyl ammonium
+ OH-
OH- released makes alkaline solution!!!
as N in Butyl amine has lone pair
Butyl amine + acid →
salt (+ water sometimes, not necessarily be in eq)
1° amine + acyl chloride →
2° amide + HCl
butyl amine + bromomethane →
if excess amine
single substitution
methyl butylamine + HBr / butylammonium bromide
butyl amine + bromomethane →
if excess halogenoalkane
multiple substitutions
ASK RJJ
butyl amine + copper(II) ions
form complex ions
has central metal ion with its covalently bonded ligand
Amines have a lone pair so can make dative covalent bonds
[Cu(H₂O)₆]²⁺ + Butyl amine -> [Cu(OH)2(H2O)4]
What are the techniques to prepare and purify organic compounds?
1 reflux
2 purify by washing
3 solvent extraction
4 recrystallisation
5 drying
6 distillation
7 bp / mp determination
Why is suction filtration good to purify organic solids?
Quicker and more dry than using just filter paper
How to recrystallise to purify organic compounds?
- Dissolve in minimal volume (so max mass of product recrystallised) of hot solvent (so solubility is higher)
- Hot filtration using hot glass funnel and heated filter paper
- cool solvent in ice
- suction filtration 5 wash solid with ice cold water
- Leave to suck dry
- Transfer to warm oven
Why is heated funnel and filter paper used in recrystallisation?
Prevent product from crystallising to maximise yield
How to remove water?
Anhydrous sodium/magnesium sulphate (very fine powder)(so when water absorbed, will stay solids, won’t dissolve)
Why is the thermometer bulb located at the sidearm in distillation?
It must read the temp of substance, gas collected
What does steam distillation do?
Heating lots of water into steam
To change the environment so reaction mixture agitated by steam
lowers bp of organic substance that’s likely to decompose
How does steam distillation lower bp of organic substance?
Reaction mixture agitated by steam
Changing the atmosphere and IMFs of environment ( from London to H bonds in water)
To its lowest decomposition point
How to use melting temperature determination?
Use mp apparatus
To measure the temp of solid
If pure substance, all melt at one temp
If impure, will melt at a range of temps
Is primary or tertiary amine more basic?
Tertiary
Because it is more e- pushing
Since it has most alkyl groups
How to make primary amines from Halogenoalkane?
NH3 + R-X -> R-NH2 + HX or NH4X
(Excess NH3, sealed tube)
How to convert nitriles to primary amine?
Add reducing agent
LiAlH4 in dry ether // H2 + Ni catalyst
Benzene + HNO3 ->
In what conditions, makes what?
Then + [H] makes what?
H2SO4 heat under reflux 50C
Makes nitrobenzene
+ 6[H] reflux in conc HCl + Sn
Make phenylamine (or aminobenzene) + water
How to make amides from acyl chloride?
Acyl chloride + 1° / 2° amine / ammonia -> HCl + amide
What reaction is the formation of polyamides?
Condensation
How to polyamide reaction?
H and Cl react like H and OH in esters
Amino acid with carboxylate on the side refluxed in excess acid will make…
Protonated Amino acid on amino group
But N has 3 H bonded to it, + charge
COOH on C2
Why is Grignard reagents good?
Lengthens carbon chain - not just by one, can be by many
Carbonyls + HCN →
OH and CN added to the carbon that had =O
hydroxynitrile produced
How to make Grignard reagent?
Haloalkane + Mg
reflux in dry ether
Why must making Grignard reagent be in dry ether?
Grignard will react with water and make
Alkane + MgXOH which we dont want
What is solid CO2?
Dry ice
Grignard + CO2 (s) →
What conditions needed?
follow by dil H+ (like HCl)
Carboxylic acid (with C added from CO2)
R-Mg-X + CO2 -> R-COOH + MgXX
Grignard + carbonyl →
Alcohol + MgXX
follow by dil H+
C forms bond with R on Grignare, =O broken, O- gains H from H+, keeps original H on C.
=O into -OH
What is the condition of electrophilic substitution involving benzene?
reflux
Why does bromine react more readily w phenol than benzene?
the hydroxyl (-OH) group in phenol increases the electron density in the benzene ring, making it more susceptible to electrophilic attack by bromine
Grignard + water ->
Alkane
How to make aminobenzene from nitrobenzene?
+ Sn + Conc HCl
Then + NaOH
How to work out if it is a electrophilic or nucleophilic, substitution or addition?
Electrophilic when mechanism arrows point away from the organic molecule. When attacked by nucleophile, electrons and arrows point towards the organic molecule.
Addition when Alkene C=C is broken to form C-C
What is the effect of a hydroxy group on a benzene ring in comparison to the ring without? (2 marks)
- lone pair from the oxygen increases electron density in the ring AND will interact with the delocalised ring of electrons
- increasing reactivity toward electrophile such as bromine
Give the steps to show how 2,4-DNPH could be used to distinguish between phenylethanone and phenylethanal. (4 marks)
- bright yellow ppt formed
- filter then recrystallise ppt
- use melting point apparatus to find melting point of each
- compare from use of database
