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The basic rules
There are some general rules which you should remember when
naming organic compounds:
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The longest unbranched chain containing the functional group
is the parent molecule or simply the longest unbranched chain
for alkanes. Remember that the longest chain can go round a
bend.
Indicate the position of the functional group with a number,
numbering from the end nearest the functional group.
Name the branches and indicate the number of branches.
Example:
Indicate the position of the branches with a number, numbering from
the end nearest the functional group.
If there is more than one branch, the branches are identified in
alphabetical order ignoring any di, tri etc.
Be aware!
Each branch needs to be numbered individually, even if they are
attached to the same carbon atom.
The rule is a comma between numbers and a dash between numbers
and letters.
Naming alkanes, alkenes and alkynes
Alkanes
The alkanes don't contain a functional group and so the branches are
numbered from the end that gives the lowest set of position numbers
for the branches.
Use the above rules to see how the names of the alkanes below are
built up.
Alkenes and alkynes
The functional group in the alkenes is the carbon to carbon double
bond.
The functional group in the alkynes is the carbon to carbon triple
bond.
The basic rules of naming apply.
The position of the double or triple bond is indicated by a number
before the -ene or -yne part of the name.
Example:
Naming alcohols, aldehydes and ketones
Alcohols
The functional group in the alcohols is the hydroxyl group (-OH).
Alcohols end in the letters -ol
The basic rules of naming apply.
The position of the hydroxyl functional group is indicated by a number
before the -ol part of the name.
Be aware!
Alcohols can also be termed primary, secondary or tertiary.
Primary has the -OH on the end of a chain.
Secondary has the -OH on a non-branched carbon atom along the
chain.
Tertiary has the -OH on a branched carbon atom along the chain.
Example:
Aldehydes
All aldehydes contain a carbonyl functional group. The carbonyl
group will never have a position number in an aldehyde as it is
always on the end of the carbon chain.
Aldehydes end in the letters -al.
The basic rules of naming apply.
Examples:
Ketones
Ketones also contain a carbonyl functional group but in ketones it is
never on the end of a carbon chain.
Ketones end in the letters -one.
The naming rules in part 1 apply as before.
Example:
Naming carboxylic acids and esters
Carboxylic acids
Carboxylic acids contain the carboxyl functional group (-COOH) The
carboxyl group will never have a position number in a carboxylic acid
as it is always on the end of the carbon chain.
Carboxylic acids end in -oic acid.
The basic rules of naming apply.
Examples:
Esters
An ester is made from an alcohol and a carboxylic acid.
Esters have their own rules for naming.
The first part of the name comes from the alcohol and it ends with the
letters -yl.
The second part of the name comes from the carboxylic acid and it
ends with the letters -oate.
Examples:
Name of Alcohol Name of Carboxylic acid Name of ester
ethanol
propanoic acid
ethyl propanoate
butanol
methanoic acid
butyl methanoate
pentanol
ethanoic acid
pentyl ethanoate
It is also possible to form names from structures.
The ester is divided between the carbon and oxygen in the ester
functional group.
The acid part contains the carbonyl group.
Examples:
Addition reactions
Addition reactions only occur with unsaturated compounds, that is,
compounds containing a carbon to carbon double bond or a carbon to
carbon triple bond. In other words, alkenes or alkynes.
Addition to alkenes
The most common addition reactions involve addition of a small
molecule like a halogen (1), hydrogen (2), a hydrogen halide (3) or
water (4). Examples of these reactions are shown below:
The small molecule always adds across the double bond. For
example, in this case of reaction (1) above the double bond is
between carbon atoms 1 and 2, so the bromine atoms will be in
position 1, 2.
All of the products are now saturated as they contain only single
carbon to carbon bonds.
The addition of hydrogen, reaction (2), is also known as
hydrogenation.
The addition of a hydrogen halide, reaction (3), to an alkene might
produce a mixture of isomers depending on how the hydrogen halide
adds across the carbon to carbon double bond.
The addition of water, reaction (4), is a very important reaction to
remember because it produces alcohols. Addition of water is also
known as hydration.
Addition to alkynes
Addition to an alkyne is a two stage process:
with the possibility of isomers being produced.
Complete addition to an alkyne will require twice the quantity of
halogen (1), hydrogen (2) or hydrogen halide (3). Examples of these
reactions are shown below:
Dehydration
Hydration involves the addition of water to an unsaturated molecule.
Dehydration is the reverse of hydration and involves the removal of
water from a molecule.
The dehydration of an alcohol is an important way to make alkenes.
Be aware!
Don't confuse hydration and dehydration with condensation and
hydrolysis (see Making and breaking esters).
Oxidation reactions
The most important oxidation reactions are oxidation of alcohols
(alkanols) and aldehydes (alkanals) using a variety of oxidising
agents.
Oxidation just means joining with oxygen.
Complete combustion is an extreme oxidation reaction.
Example: Complete combustion of methanol.
2 CH3OH + 3 O2
2 CO2 + 4 H2O
Alcohols burn in oxygen to produce carbon dioxide and water.
In organic chemistry, oxidation can mean both adding oxygen or
removing hydrogen.
The oxidations to remember are:
Example: oxidation of ethanol (primary alcohol).
Example: oxidation of propan-2-ol (secondary alcohol).
Both examples show that oxidation leads to an increase in the
oxygen to hydrogen ratio.
Tertiary alcohols are not easily oxidised because, unlike primary and
secondary alcohols, they do not have a hydrogen attached to the
same carbon atom as the hydroxyl group.
Of course, the opposite of oxidation is reduction and the previous two
examples can also go in reverse:
Example: reduction of ethanoic acid
This example shows how the oxygen to hydrogen ratio decreases
during reduction.
The oxidising agents
It is important to remember the colour changes which occur in the
reactions, both starting and final colours.
Oxidising reagents must always be reduced and the ion-electron
equations for the reactions are on page 11 of the Higher data booklet.
Summary of oxidising agents:
Oxidising
Change in appearance
agent
Copper(II)
black solid
brown solid
oxide
Acidified
orange solution
(blue)potassium
green solution
dichromate
solution
Benedict's or
blue solution
orangeFehling's
red precipitate
solution
Tollen's
colourless solution
Reagent
silver mirror
Reason
Cu2+ + 2e-
Cu
Cr2O7 2+(aq) reduced
to Cr3+(aq)
Cu2+ + e-
Cu+
Ag+(aq) + eAg(s)
Prescribed practical activity
Oxidising agents can be used to distinguish between aldehydes and
ketones. Because aldehydes can be oxidised, they will produce the
colour changes in oxidising agents shown above. Ketones can't be
easily oxidised and so do not produce these colour changes.
Making and breaking esters
An ester is made from a carboxylic acid and an alcohol.
This is a condensation reaction, where two molecules join together
to form one larger molecule (the ester) and a small molecule, usually
water.
Example: formation of ethyl propanoate.
The ester link is formed by the reaction of a hydroxyl group with a
carboxyl group.
The reaction of an alcohol with a carboxylic acid is, in fact, a
reversible reaction. In the reaction, some of the ester molecules
formed are split up again into the alcohol and carboxylic acid they are
made from. This happens when water reacts with the ester link. This
is a hydrolysis reaction.
A hydrolysis reaction is one where a large molecule is split into two
smaller molecules by reaction with water.
When an alcohol reacts with a carboxylic acid an equilibrium is
produced. The equation for the reaction contains a double arrow. The
forward reaction is a condensation reaction and the reverse reaction
is a hydrolysis reaction.
Example: formation of methyl ethanoate.