Module 4 - [ch12,13] (alkanes alkenes)

crude oil among the most stable organic compounds unreactive used as fuels saturated hydrocarbons

saturated hydrocarbons only single covalent bonds each carbon makes 4 bonds

each carbon atom is surrounded by 4 bonded pairs tetrahedral 109.5

separation by (differences in) boiling point

as chain length increases, molecules have larger surface area more surface contact possible between molecules london forces between molecules are greater so more energy is required to overcome these forces

branched isomers have lower boiling points

C - C C - H sigma bonds are strong C - C are non-polar barely any difference in electronegativity of C and H so can also be described as non-polar

alkane + oxygen -> carbon dioxide + water gives out heat

limited supply of oxygen toxic gases such a carbon monoxide (CO) soot

in the presence of sunlight UV radiation provides initial energy for reaction to take place substitution reaction methane + bromine -> bromomethane

initiation Br - Br -> Br. + Br. homolytic fission propagation CH4 + Br. -> CH3. + HBr CH3. + Br2 -> CH3Br + Br. termination Br. + Br. -> Br2 CH3 + CH3 -> C2H6 CH3. + Br. -> CH3Br

further substitution substitution at different positions on the carbon chain

unsaturated hydrocarbons contain a C=C double bond

overlap of adjacent p-orbitals below and above the Carbon atoms can only be made after a sigma bond is formed

three regions of electron density around each carbon atom trigonal planar 120

they have the same structural formula but different arrangement of the atoms in space EZ isomerism (only in compounds with C=C) optical isomerism

. C=C double bond . different groups attached to each carbon atom of the double bond

a special case of EZ isomerism where one of the attached groups on each carbon atom of the double bond must be the same

examine the atom directly attached to the carbon atoms of the double atom greater atomic number = higher priority if there is no difference, continue down chains till point of difference and compare those atoms

if highest priority groups are on the same side (Z) on opposite sides (E)

the pi-bond it is outside of the double bond, therefore more exposed a pi bond readily breaks and alkenes undergo addition reactions easily

alkene + H2 -> alkane

alkene + halogen -> something

bromine water tests for unsaturation (the double bond) orange -> colourless