organic chemistry

ALKANES

SP3 hybridisation, tetrahedral molecules (109.5º)

non-polar ; made up of C-C and C-H bonds

saturated hydrocarbon

down the series of alkanes, viscosity, branching increases while flammability and volatility decreases

MECHANISM : FREE-RADICAL SUBSTITUTION (initiation, propagation and termination steps)

CHEMICAL REACTIONS OF ALKANES

combustion

substitution by chlorine and bromine

cracking : thermal and catalytic

catalytic reforming

ALKENES

sp2 hybridisation, trigonal planar molecules (120º)

contains c=c, which is the functional group

c=c bond, therefore unsaturated hydrocarbon

the c=c contains one sigma and one pi bond

positional and geometrical isomerism may arise

mechanism: ELECTROPHILIC ADDITION

REACTIONS OF ALKENES:

combustion

addition reactions (hydrogenation, addition of halogens, addition of hydrogen halides, addition of steam)

oxidation

polymerisation

ARENES AND BENZENE RINGS (aromatic hydrocarbons)

SP2 hybridisation, trigonal planar (120º)

BENZENE : colourless liquid, boils at 80º, obtained by distillation of coal/bitumen/wood

burn with a luminous, smoky flame

all c-c and c-h bonds are of the same length

the π-electron system consists of 6 electrons delocalised over the 6 carbon atoms

MECHANISM: ELECTROPHILIC SUSBTITUTION (benzene) + FREE-RADICAL SUBSTITUTION (methylbenzene)

REACTIONS OF BENZENE AND METHYLBENZENE

substitution reactions with chlorine and with bromine

nitration

Friedel-Crafts alkylation and acylation

complete oxidation of the side-chain to give a benzoic acid

hydrogenation of the benzene ring to form a cyclohexane ring

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