A2 Structures, Reactions And Properties Of Commercially Important Organic Compounds Flashcards
General formula for alkanes
CnH2n+2
Structural isomer
Have the same molecular formula but different structural formula.
Chain isomer
Molecules with the same molecular formula but different arrangement of carbon atoms.
Naming branched chain alkanes
1) find the longest carbon chain (name eg butane)
2) find any side chains and name (eg methyl)
3) number the side chains
Eg 2-methylbutane
Complete combustion
- short chain alkanes are valuable fuels
- when there is plentiful supply of oxygen it undergoes complete combustion to form carbon dioxide and water.
Uses of Methane and it’s equation for complete combustion
- main constituent of natural gas used for heating and cooking
- CH4 + 2O2 = CO2 + 2H2O
Incomplete combustion
When there is a limited amount of oxygenation carbon monoxide gas, or carbon and water is formed.
Incomplete combustion of methane
- CH4 + 3/2 o2 = CO + 2H2O
- CH4 + O2 = C + 2H2O
What make’s intermolecular forces stronger (in alkanes) ?
- alkanes have induced dipole dipole forces
- these get stronger when there are more electrons
- larger alkane- stronger intermolecular force
How can a change of shape affect the boiling point of alkanes?
- when the surface area of the molecule decreases but the number of electrons stay the same the boiling point decreases.
- this is because there is less surface contact and weaker intermolecular force.
Formula for alkenes
CnH2n
Positional isomerism
Molecules with the same molecular formula which have the functional group on different positions in the molecule.
Functional group isomerism
Molecules with the same molecular formula but different functional groups.
- cycloalkanes and alkenes can show functional isomerism. Cycloalkanes have the same formula as alkenes CnH2n
Stereoisomer
molecules with the same structural formula but a different arrangement of the atoms in space eg but-2-ene CH3CH = CHCH3
Why do stereoisomers occur?
- double bonds restrict rotation
- when 2 different groups are attached to the carbons in the double bond