ORGANIC CHEMISTRY NOTES
Homologous series- a group of organic compounds containing the same functional group in which each
successive member in the unit increases by the unit -CH2
Characteristics of a homologous series:
1. All members of a particular series have the same functional group - COOH for carboxylic acids
2. The members of a particular series increase by the unit -CH2
3. All members of a series have similar chemical properties because they have the same functional
group
4. Each member in the particular series have physical characteristics that chnage in a regular way, for eg
as the number of carbons in the straight chain alkane increases, the BP increases.
Reactions of alkanes:
1. Cracking - Catalysts are Aluminium or silicon oxide
temperature w catalyst - 400 - 500 degrees celsius
temperature w/o catalyst - 700 - 900 deg celsius
2. Free Radical Substitution
Free radical: a species or fragment of species that has an unpaired electron
Stages: Initiation, Propagation, Termination
Substitution takes place in UV light
3. Combustion
Reactions of alkenes
1. Oxidation
Using hot KMNO4 - alkenes become aldehydes, ketones, carboxylic acids / CO2
Using cold KMNO4 - alkenes become diols
2. Hydrogenation - to form alkanes
Nickel - catalyst
140 deg celsius
3. Reaction with steam - catalyst: phosphoric acid
4. Addition of hydrogen halides: Electrophilic addition
Electrophile - a species or fragment of species that has a partially positive or positive charge and attacks
electron rich areas of molecules
eg H+
5. Reaction with hot H2SO4 to from alchols
Under reflux conditions, the acid reforms
Reactions of alcohols
1. Oxidation
Primary alcohols oxidised to aldehydes and further to carboxylic acids
Secondary alcohols oxidised to ketones
2. Reduction with carboxylic acids (Esterification)
To form esters
3. Reduction of alcohols
To form alkenes
4. Iodoform test
alkali environment
includes secondary alcohols which have a methyl group on the same carbon as the OH group.
The iodine replaces all the hydrogens on the methyl group forming triiodomethane
Reactions of Halogenalkanes
Primary halogenoalkanes - halogenoalkanes which contain a halogen bonded to a carbon that is bonded
to one other carbon
Secondary halogenoalkanes - halogenoalkanes which contain a halogen bonded to a carbon that is
bonded to two other carbons
Tertiary halogenoalkanes - halogenalkanes which contain a halogen bonded to a carbon that is bonded
to three other carbons
1. Primary halogenoalkanes undergo SN2 reaction- Substitution nucleophilic 2nd order reaction
Both the primary halogenoalkane and the nucleophile are involved in the rate determining step which is
the only step.
2. Tertiary halogenolalkanes undergo SN1 reaction
Only the halogenoalkane is involved is involved in the rate determining step
Tertiary alcohols are formed
Reactions of Carbonyl groups
Testing for carbonyl groups
1. Brady's reagent - yellow to orange if carbonyl group is present
2. Tollen's reagent - Silver mirror test. Is a mexture of silver complex ions in excess ammonia. If
aldehydes are present, a silver mirror is formed because the silver complex
ions are reduced
3. Fehling's Reagent - substance is warmed with complex (ii) ions. Aldehydes are oxidised to carboxylic
acids. Fehling's changes from blue to orange/brick red
Oxidation - KMNO4 or K2CRO7
Reduction of carbonyl groups - using lithium aluminium hydride
Aldehydes reduced to primary alcohols
Ketones reduced to secondary alcohols
AROMATICS
Benzne reactions:
Chlorination of Benzene
Reagents : Catalyst : Ferric chloride / Iron (iii) chloride, Chlorine molecule
Nitration of Benzene
Reagents : Concentrated nitric and sulphuric acid (catalyst). Nitronium ion is the electrophile.
Methylbenzene/Toulene reactions:
Methyl groups are 2,4 directing. Have a positive inductive effect. The carbon in methyl group is positive.
The electrons are pushed the ring of delocalised pi electrons
Nitration of Toulene:
Reagents: Sulphuric acid (catalyst) and Nitric acid
Products : toulene + nitril group, water and sulphuric acid
Bromination of Toulene
Reagents: toulene + Br2 ---> Toulene + Br + HBr
Nitrobenzene reactions
The nitro groups have a negative inductive effect. The nitro groups pull electrons to itself away from the
ring of delocalised pi electrons in the benzene. The odd bonding between
nitrogen and oxygen causes the negative inductive effect. Nitrogen should have 3 bonds but it has 4
bonds while oxygen has an unpaired electron which causes a negative charge.
The double bond on the oxygen alternates between the two oxygen atoms. In order for the nitro group
to be stable, the electrons are shared between the two oxygens.
So as a result of this, conjugative effect, electrons are being pulled from the benzene ring to stabilise
that portion of the group, making the benzene ring less reactive.
The electrons are being pulled from the ring because nitrogen is more electronegative than carbon and
facilitates the pulling away of electrons.
The nitro group is 3 directing
Reduction of nitrobenzene
Reagents: Concentrated HCL and tin
products : aniline/phenylamine/benzeneamine + water (involved in diazotisation reaction with nitrous
acid)
Nitration of benzene
Acid mixture - conc nitric and sulphuric acid
Phenols
very reactive
- Halogens : ring extends, oxygen included, oxygen donates electrons to the ring
- Sodium : forming sodium phenoxide + water
-Magnesium and Aluminium : magnesium/aluminium phenoxide + hydrogen gas
- acid halides eg. ethanoyl chloride : ester + HCL
- Diazotisation and coupling reactions involving phenol