AS Organic Chemistry Summary

AQA AS ORGANIC CHEMISTRY

INTRODUCTION TO ORGANIC CHEMISTRY:
o Nomenclature -
Homologous Series –
 Families of (organic) compounds with the same functional group & general formula.
 Each member differs by CH2.
 Similar chemical properties & show a graduation in physical properties.




General Rules For Naming Organic Compounds –
1. Count LONGEST carbon chain.
2. Identify any functional groups / branches.
3. Functional groups take precedence over branched chains in giving the
lowest number. E.g. 3-methylbut-1-ene is correct BUT not 2-
methylbut-3- ene.
4. Where there are two or more of the same groups > di-, tri-, tetra-, penta-
or hexa- are used & methyl or ethyl for number of branches.
5. If there is more than one functional group or side chain, the groups are
listed in alphabetical order (ignoring any di, tri).
6. Words are separated by numbers with dashes & numbers separated by
commas.
 Examples -

, AQA AS ORGANIC CHEMISTRY
Definitions –
 General formula = an algebraic formula that describes all members of a homologous (organic) series. E.g.
Alkane (CnH2n+2).
 Empirical formula = the simplest whole number ratio of atoms of each elements in a compound. E.g. Ethane
molecular formula (C2H6) > empirical (CH3).
 Molecular formula = the actual number of atoms in each element in a compound. E.g. Ethane (C2H6).
 Structural formula = shows arrangement of atoms of a compound, without
showing the bonds. E.g. Butane (CH3CH2CH2CH3).
 Displayed formula = shows all atoms & all covalent bonds present in a
compound.
 Skeletal formula = shows the simplified organic formula, shown by removing
hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated
functional groups.
 Functional group = a group of atoms which are responsible for the characteristic
reactions of a compound > molecules with the same functional group will belong
to the same homologous series.



o Isomerism -
 4 types of structural isomer = position, functional group isomer & chain isomer.
 Structural isomer = compounds that have the same molecular formula but different structural formula.
 Position isomer = compounds that have the same molecular formula but functional groups are in different
positions.





Functional group isomer = compounds with the same molecular formula but have different functional groups.




 Cha
in isomer =
compounds
with the
same
molecular
formula but
different
branching in the carbon chain.

, AQA AS ORGANIC CHEMISTRY




Stereoisomerism -
 Stereoisomer = compounds with the same molecular & structural formula but a different arrangement of
atoms in space.
 Alkenes can exhibit a type of isomerism called E-Z stereoisomerism.
 E-Z isomers exist due to restricted rotation about the C=C bond & there are two different groups /atoms
attached both ends of the double bond.




Cahn–Ingold–Prelog (CIP) priority rules -
1. Compare the atomic number of the atoms directly attached to each side of
the double bond > the atom of higher atomic number is given priority.
2. If the atoms are the same, consider the atoms at distance 2 from the
double bond.



ALKANES:
o Fractional Distillation Of Crude Oil -
Alkanes are saturated hydrocarbons > compounds containing hydrogen & carbon ONLY with ONLY C-C single
bonds between carbon atoms.

 Petroleum (crude oil) = mixture of mainly straight-chained & branched alkanes than can be separated by
fractional distillation.
1. Crude oil heated in furnace, until a portion changes state into vapour.
2. The liquid-vapour mixture is passed up into a fractionating column > has a temperature gradient (cooler at
top vs bottom).
3. Each fraction reaches the bubble cap – point of condensation (just below alkanes boiling point) where is
condenses & so piped off.
4. Short chain alkanes = collected at top > cooler, lower bp, decrease in VDW forces, less points of contact &
less energy needed to break the C-C single bonds. AND VICE VERSA.