A* A-Level organic Chemistry Notes:
,Introduction to organic chemistry:
1. Empirical formula: The simplest whole-number ratio of atoms of each element in a
compound.
2. Molecular formula: The actual number of atoms of each element in a molecule.
3. General formula: he simplest algebraic formula for a homologous series
4. Structural formula: Shows the minimal detail about how atoms are bonded without drawing
bonds.
5. Displayed formula: A full representation of all atoms and bonds in a molecule.
6. Skeletal formula: A simplified structure where carbon atoms are represented by the ends of
lines, and hydrogens are omitted.
As stated in the definition when drawing the skeletal formula, we do not add the hydrogens, and the
carbon atoms are represented by the ends of lines.
Homologous series:
Homologous series: A family of organic compounds with the same functional group and general
formula, where each successive member differs by a CH₂ unit.
Functional group: An atom or group of atoms responsible for the chemical reactions of a compound.
● Trend in physical properties
● Same chemical properties
,When a compound contains more than 1 functional group, we prioritise the highest precedence group
and this functional group will take the suffix.
Carboxylic acids > aldehydes > ketones > alcohols > alkenes > halogenoalkanes
General rules when naming organic compounds:
● Always count the longest chain and understand the name of the compound. (E.g. 5 carbons
would suggest pent)
● Look for branched chains, and how many carbons in the branch
● Add the prefix for each branch
● When looking for the suffix, the position of the functional group tells us this.
● To find the number, count from the end of the chain which gives the lowest number.
● For aldehydes, carboxylic acids and nitriles, the functional group is always on carbon 1.
Alkenes:
● Alkenes have the general formula CnH2n.
● Alkenes may have E/Z at the start of the name, this is due to stereoisomerism which we will
explore later on.
● If 2 double bonds are present, then the suffix would be diene.
● If alcohol or carboxylic acid functional groups present, then the suffix will not go at the end.
We will use -en instead, so be careful when numbering.
, Halogenoalkanes:
● Name the halogens in alphabetical order (Fluoro-, Chloro-, Bromo-, Iodo-).
● Include position numbers for halogens and alkenes, making sure they have the lowest
number possible.
● If multiple halogens or alkenes, use prefixes (di-, tri-, tetra-).
● As alkenes have priority over haloalkanes, the haloalkane functional group goes in the middle.
● CH₃CBr=CHCl → 2-Bromo-1-chloroprop-1-ene
Alcohols:
● Alcohols end in -ol.
● If there are 2 or more alcohol groups, we use diol, triol etc. However if there are more than 1
alcohol group, when naming them, never forget the e.
● If the -OH group is present in a compound with a higher priority group such as -COOH, we use
-hydroxy instead of -ol.
,Introduction to organic chemistry:
1. Empirical formula: The simplest whole-number ratio of atoms of each element in a
compound.
2. Molecular formula: The actual number of atoms of each element in a molecule.
3. General formula: he simplest algebraic formula for a homologous series
4. Structural formula: Shows the minimal detail about how atoms are bonded without drawing
bonds.
5. Displayed formula: A full representation of all atoms and bonds in a molecule.
6. Skeletal formula: A simplified structure where carbon atoms are represented by the ends of
lines, and hydrogens are omitted.
As stated in the definition when drawing the skeletal formula, we do not add the hydrogens, and the
carbon atoms are represented by the ends of lines.
Homologous series:
Homologous series: A family of organic compounds with the same functional group and general
formula, where each successive member differs by a CH₂ unit.
Functional group: An atom or group of atoms responsible for the chemical reactions of a compound.
● Trend in physical properties
● Same chemical properties
,When a compound contains more than 1 functional group, we prioritise the highest precedence group
and this functional group will take the suffix.
Carboxylic acids > aldehydes > ketones > alcohols > alkenes > halogenoalkanes
General rules when naming organic compounds:
● Always count the longest chain and understand the name of the compound. (E.g. 5 carbons
would suggest pent)
● Look for branched chains, and how many carbons in the branch
● Add the prefix for each branch
● When looking for the suffix, the position of the functional group tells us this.
● To find the number, count from the end of the chain which gives the lowest number.
● For aldehydes, carboxylic acids and nitriles, the functional group is always on carbon 1.
Alkenes:
● Alkenes have the general formula CnH2n.
● Alkenes may have E/Z at the start of the name, this is due to stereoisomerism which we will
explore later on.
● If 2 double bonds are present, then the suffix would be diene.
● If alcohol or carboxylic acid functional groups present, then the suffix will not go at the end.
We will use -en instead, so be careful when numbering.
, Halogenoalkanes:
● Name the halogens in alphabetical order (Fluoro-, Chloro-, Bromo-, Iodo-).
● Include position numbers for halogens and alkenes, making sure they have the lowest
number possible.
● If multiple halogens or alkenes, use prefixes (di-, tri-, tetra-).
● As alkenes have priority over haloalkanes, the haloalkane functional group goes in the middle.
● CH₃CBr=CHCl → 2-Bromo-1-chloroprop-1-ene
Alcohols:
● Alcohols end in -ol.
● If there are 2 or more alcohol groups, we use diol, triol etc. However if there are more than 1
alcohol group, when naming them, never forget the e.
● If the -OH group is present in a compound with a higher priority group such as -COOH, we use
-hydroxy instead of -ol.
