unit 4 Flashcards
Explain the structure of Benzene?
There are two ways of representing the structure of benzene.
- Kekule model ( the pi electrons are isolated in the three double bonds)
- delocalised model.( The pi electrons are delocalised over the whole benzene structure)
Evidence supports delocalised
- delta H hydrogenation -208 not -360
- X rays show bond length the same
- benzene does not decolourise bromine water. requires catalyst. should go orange to colourless.
Why does benzene take part in substitution reaction?
The benzene is fairly stable and substitution reactions allow it to retain its delcalised system and hence its stability.
Decribe the nitration(NO2) of Benzene.
Conc HNO3 and Conc H2SO4 added 50 degrees
HNO3+H2SO4===>HSO4- + NO2+ + H20
The NO2 is an electrophile that undergoes electrophilic substitution.
Hescribe the halogenation of benzene?
Electrophilic substitution reaction.
Requires: halogen carrier e.g AlCL3 room temp, in the dark.
heterolytic fission of the Cl2 occurs.
Cl2 +AlCL3====>Cl+ + AlCl4-
What is a Halogen carrier?
it is an electron defficient molecule that helps produce an electron defficinet halogen atom or alkyl group.
Why can the reaction of Phenol (C6H5OH) be treated in two parts?
*The OH group and benzene group react differently, however each one affects the other.
Explain the reactions of the OH group in phenol.
*Acts as an acid as it loses a proton, the presence benzene ring weakens the OH bond.
Explain the activation of the benzene rings in phenol.
The lone pair of electrons from the oxygen are delocalised on the benzene ring, increasing th electron density in 2,4,6, therefore they decolourise bromine water.
What are some uses for phenols?
- Plastics
- resins in paint.
- Antiseptics
- Disinfectants
What are some uses for esters?
- In perfumes and flavourings
- Solvent for antibiotics and drugs
- In biodiesel
Explain Ester hydrolysis?
*Acid Hydrolysis
HCL(catalyst) heated under reflux
get OH in the end.
*Alkaline hydrolysis
NaOH heated under reflux
forms OH and O-Na+
What are fatty acids?
Fatty acids have a long carbon chain with a carboxylic aci group at the end.
- no double bond= saturated
- double bond=unsaturated
How do you name fatty acids?
anoic if its unsaturated
enoic if its saturated.
*Shorthand names
N.O of carbon atoms, double bonds(positions of double bonds)
What are trans fatty acids and how do they harm the body?
Trans fatty acids are formed from the hydrogenation of vegetable oils, this raises low density lipoproteins, causin risk of obesity coronary heart disease.
What is a tryglyceride?
It is a triester of glycerol(propan 1,2,3 triol) and fatty acids.
How do you make bio diesel.
- A process called transesterification
- Sodium hydroxide catalyst.
- Tryglyceride + methanon/ethanol ===> biodiesel + glyceride.
What is a primary amine?
One in which the nitrogen atom is only attached to one carbon chain.
How do you name secondary and teriary amines?
Secondary has one N in the biginning
tertiary has N,N in the beginning
e.g N,N-diethyl propylamine
N-methyl butylamine
Explain the basicity of amines?
They are proton acceptors
base+acid===>salt
How do you make aromatic arenes?
- Nitrobenzene is reduced to phenylamine and water
* tin and conc HCL heated under reflux
State the two steps for the industrial production of dyestuffs.
1)Diazotisation
phenylamine, nitrous acid(HNO2) and 2HCL below 10d
* benzene diazonium chloride and water is formed
** HNO2 is formed from NaNO2+HCL.
2) Coupling
* benzene diazonium chloride + phenol + NAOH
* forms the product plus NaCl +H2O
What are alpha amino acids?
They have both the carboxyl group and basic amine group attached to the same carbon.
What is a zwitterion@
Dipolar ionic form, formed by the donation of H+ from COOH to NH2
How are peptide bonds formed?
From condensation reactions water is added.
Hydrolysis of polypeptides?
- Acid hysrolysis
- heated under reflux HCl + water for 24hrs
Alkaline Hydrolysis
*NaOH 100 degrees
What are condensation polymers?
The joining of two monomers by the removal of a small molecule such as water or HCl
