6. Organic Molecules (REACTIONS OF ALKANES)

Cn H2n+2

Saturated - all carbon bonds are single

Heterolytic fission Homolytic fission

When the covalent bond breaks unevenly so electrons are distributed unevenly to form a cation and ion. The cation receives both of the electrons in the bonding pair

When the covalent bond breaks evenly so electrons are distributed equally to form 2 radicals

Radicals are particles that have an unpaired electron (represented by a dot) –> due to unpaired electron, radicals are highly reactive

When a hydrogen atom gets substituted by a halogen (chlorine/bromine) in a photochemical reaction ( a reaction that requires UV light)

• Initiation - Creation of radicals • Propagation (2 stages) - reactions that produce new radicals • Termination - Removal of radicals (This is a chain reaction)

Initiation - sunlight / uv light provides enough energy to break the Cl-Cl bond. This is called photodissociation. The bond equally breaks forming 2 highly reactive radicals through process of HOMOLYTIC fission

Propagation - 1) Chlorine radical react with methane. Chlorine radical removes a hydrogen to produce a methyl radical and the second product - HCL 2) This methyl radical can then react with a chlorine molecule (not a chlorine radical) to produce the desired product of chloromethane and a chlorine radical 3) New chlorine radical can react with methane and so on…… causes a chain reaction

Termination - 2 radicals react together to form a stable non - radical

You create a mixture of products as substitution happens anywhere on the chain –> Excess Cl2 promotes further substitution as its a chain reaction, creating more products and therefore issues for separating the mixture as di,tri and tetrachloromethane can be produced) –> Add excess methane to combat as there is more chance of a chlorine radical colliding with a methyl molecule and not a chloromethane molecule

Straight chain or branched organic compounds e.g. C2H5OH

Organic compounds containing the benzene ring

Fuels and lubricants

1) heated in furnaces and passed as a vapour into fractionating column from the bottom 2) temperature gradient: hotter near bottom 3) as the vapour rises, different fractions condense at different heights depending on boiling temperatures. Short-chain alkanes condense at the top (low boiling point) and long-chain condense lower down (higher boiling point)

• larger molecules with longer chains and higher boiling temperatures condense at the bottom • smaller molecules with more bracnhes and shorter chains and lower boiling temperatures condense near the top (pack less closley reducing stength of london forces) • some of the hydrocarbons are dissolved gases so rise to the top of column without it condensing

splitting of large hydrocarbons to smaller alkenes and shorter alkanes by breakage of C-C bonds Main product for thermal cracking: aromatic compounds Main product for catalytic cracking: smaller alkanes and alkenes

1) shorter chain alkanes and alkenes formed 2) Alkenes are useful starting materials in organic synthesis + used for making polymers + plastics 3) Shorter chain alkanes are more in demand / higher value / can be used as fuel. The smaller alkanes are used for motor fuels which burn more efficiently.

Thermal cracking - requires high pressure and high temperature - 1200K, 7000Kpa Catalytic cracking - requires 720K, normal pressure and a ZEOLITE catalyst

Reforming hydrocarbons turns straight chain hydrocarbons into branched and cyclic hydrocarbons. branched and cyclic hydrocarbons burn more efficiently and easily ( branches get in the way so less london forces as they pack together less) than straight chain hydrocarbons and are used to give fuels a higher octane number - used for making motor fuels Reform hydrocarbons to also reduce reduce knocking

A material that releases energy when it burns

when burning in excess oxygen

When there is a limited supply of oxygen