3.
1 Introduction to Organic Chemistry
• Organic Chemistry is the study of carbon chemistry as carbon has the ability to join
together in chains, rings, balls etc.
• Carbon also joins with other elements easily such as oxygen, hydrogen, nitrogen,
phosphorous and the halogens.
• Carbon can join in many different ways and shapes.
Bonding in organic compounds:
• As carbon is in Gp4 of the periodic table it has 4 single outer shell electrons meaning it
forms 4 covalent bonds only.
• Carbon can form more than one bond with itself:
4 bonds only A double bond and 2 single bonds to hydrogen = 4
The Structure of Organic chemistry
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Definitions:
Hydrocarbon:
A compound that contains only hydrogen and carbon
Saturated:
A compound that contains single carbon – carbon bonds only
H H H H
H C C C C H
H H H H
Unsaturated:
A compound that contains one or more carbon – carbon double bonds
Molecular formula:
The actual number of atoms of each element in a compound
eg Hexane’s molecular formula is C6H14
Empirical formula:
Simplest whole number ratio of atoms of each element in a compound
eg Hexane’s empirical formula is C3H7
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Displayed formula:
Shows all the atoms and bonds in a molecule
H H H H
H C C C C H
H H H H
Structural formula:
Shows how the atoms in a molecule are arranged
Skeletal formula:
Shows the shape of the carbon skeleton
• A good way to approach this is to count and number the carbons. This can then be
transposed to the carbon skeleton:
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Further examples:
Structural formula:CH3CH2CH2CH3 Structural formula:CH3CH(CH3)CH2CH2CH3
Homologous series:
Is a family of compounds containing the same functional group and having the
same general formula. Each successive member has a different carbon chain
length by CH2
CH3OH CH3CH2OH CH3CH2CH2OH CH3CH2CH2CH2OH
Functional group:
Is an atom or group of atoms which gives an organic compounds its particular
chemical properties
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Functional groups
• Organic Chemistry is studied in a systematic way because each different group of atoms
attached to a carbon atom has its own characteristic set of reactions.
Functional group Formula Prefix (side Suffix (functional
chains) group)
Alkane C-C -ane
Halogenoalkane –F Floro -
– Cl Chloro -
– Br Bromo -
–I Iodo -
Alkene C=C -ene
Increasing priority when naming
Amine – NH2 -amine
Alcohols – OH Hydroxy - - ol
(if other
functional
groups are
present)
Aldehydes - al
- CHO
Ketones - one
Nitrile – nitrile
Acyl chlorides – oyl chloride
Ester – oate
Carboxyllic acids - oic acid
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Nomenclature
• Naming organic compounds according to the IUPAC system
The Alkanes:
• This is a homologous series of saturated hydrocarbons:
• All the molecules end in 'ane'
• The alkanes and their names are outlined in the table below:
• The number of carbons represent a name (later):
No of
Name Formula
C's
1 Methane CH4
2 Ethane C 2H 6
3 Propane C 3H 8
4 Butane C4H10
5 Pentane C5H12
6 Hexane C6H14
7 Heptane C7H16
8 Octane C8H18
9 Nonane C9H20
10 Decane C10H22
• Organic molecules are usually made up from:
Carbon chain
Side chains (alkyl groups)
Functional groups
• They are named in the following way
Stem
The longest carbon chain - the main name (in the middle)
Prefix
Added before the main name - pre - main name (side chains and some functional groups)
Suffix
Added after the main name - post - main name (functional groups)
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Alkyl groups:
• If you remove a hydrogen from an alkane you have a group that has a bond that can join to
the main carbon chain.
• Based on the alkanes the ending of these are changed to alkyl
Methane Methyl
• The first six alkyl side chains are in the table below:
No of Name Formula
C's
1 Methyl – CH3
2 Ethyl – C2H5
3 Propyl – C3H7
4 Butyl – C4H9
5 Pentyl – C5H11
6 Hexyl – C6H13
Naming rules:
1) Look for the longest continuous carbon chain – Stem
2a) Look for the functional groups – Suffix (can be a prefix)
2b) Count the position of the functional group and assign the lowest number. Use the lowest
number – number goes between Stem and Suffix
3a) Look for alkyl side chains – Prefix
3b) Count the position of the alkyl side chain and assign the number in line with the count in (2)
– number goes before the Prefix
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Example 1:-
1) Look for the longest continuous carbon chain – Stem
4 carbons, therefore: … But…
2a) Look for the functional groups – Suffix (can be a prefix)
2b) Count the position of the functional group and assign the lowest number. Use the lowest
number – number goes between Stem and Suffix
No other functional groups except alkane, therefore: …ane
…Butane
3a) Look for alkyl side chains – Prefix
3b) Count the position of the alkyl side chain and assign the number in line with the count in (2)
– number goes between Prefix and Stem
There’s a methyl side chain on carbon ‘2’, therefore: 2 – methyl…
2 – methylButane
*However, as methyl can only ever be on C2, we drop the ‘2’
MethylButane
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Example 2 - Additional side chains
1) Look for the longest continuous carbon chain – Stem
5 carbons, therefore: … Pent… (keeping the numbers low)
2a) Look for the functional groups – Suffix (can be a prefix)
2b) Count the position of the functional group and assign the lowest number. Use the lowest
number – number goes between Stem and Suffix
No other functional groups except alkane, therefore: …ane
…Pentane
3a) Look for alkyl side chains – Prefix
3b) Count the position of the alkyl side chain and assign the number in line with the count in (2)
– number goes between Prefix and Stem
There’s a 2 - methyl and a 3 – ethyl side chain, these are put in alphabetical order,
therefore:
3 – ethyl, 2 – methyl…
3 – ethyl, 2 – methylPentane
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Example 3 - Side chains and a functional group
1) Look for the longest continuous carbon chain – Stem
4 carbons, therefore: … But… (keeping the numbers low)
2a) Look for the functional groups – Suffix (can be a prefix)
Alcohol functional group present …ol
• For functional groups that start with a vowel, insert ‘an’ on the end of the stem
…Butan…ol
2b) Count the position of the functional group and assign the lowest number. Use the lowest
number – number goes between Stem and Suffix
Alcohol functional group on carbon 1, therefore …1 – ol
…Butan – 1 – ol
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3a) Look for alkyl side chains – Prefix
3b) Count the position of the alkyl side chain and assign the number in line with the count in (2)
– number goes between Prefix and Stem
There’s are two 2 - methyl side groups
• For identical side groups of the same carbon we use di - 2, tri - 3, tetra - 4
2,2 - dimethyl…
2,2 – dimethylButan - 1 - ol
• Numbers are separated from names by hyphens.
• Numbers are separated from other numbers by commas
Example 4: Cyclic alkanes
• If an alkane is cyclic we use the prefix
‘Cyclo’
cyclohexane
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Other examples:
• These contain a C=C, the ending of the name changes to ‘ene’ and we have to put a
number to where the double bond is in the carbon chain:-
But – 1 – ene
But – 2 – ene
Names for Halogenoalkanes
Stem - Longest chain = 3C = prop
Prefix - Functional group = Chloroprop
Chloro is on carbon 1 = 1 chloroprop
No suffix = ane = 1 chloropropane
Names for alcohols
Stem - Longest chain = 5C = pent
Suffix - Functional group =OH (suffix starts
with a vowel) = pentan ol
OH is on carbon 3 = pentan - 3 - ol
Names for aldehydes
Stem - Longest chain = 4C = but
Suffix - Functional group = CHO (suffix starts with a
vowel) = butanal
The 'al' does not need a number as all aldehydes are
at the end of the molecule.
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More than one of the same type of functional group
Stem - Longest chain = 4C = but
Prefix - Functional group = Cl on carbon 1
= 1 - chloro
Functional group = Br on carbon 2 (prefix)n = 2 -
bromo
Functional groups are named alphabetically: 2 -
bromo - 1 - chlorobut
No suffix = ane = 2 - bromo - 1 - chlorobutane
Names for many of the same functional groups:
Longest chain = 2C = eth
Functional group = Cl, (2 x on carbon 1)
and 2 x on carbon 2 (prefix), numbers first
then how many chlorines: 1,1,2,2 -
tetrachloroeth
No suffix = ane = 1,1,2,2 -
tetrachloroethane
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Isomerism
• The molecular formula only tells you how many atoms of each element are present.
• It does not give you the structure.
• Molecules often have the same molecular formula but very different structures. These are
called Isomers and there are many types.
Structural Isomers
• These have different structures using the same atoms.
Structural Isomer:
Are compounds with the same molecular formula but a different structural
formula
• There are 3 types of structural isomers
Stereo Isomers
• These have the same structures using the same atoms but the atoms are arranged
differently in space.
Stereo Isomer:
A Molecule with the same structural formula but its atoms are arranged differently
in space
• There are 2 types of stereoisomers
1) Geometric or E/Z Isomerism (in Alkenes)
2) Optical (in A2 Year)
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Activity 1:
• Use the molymods to make and draw as many molecules as possible using all of 5
carbons and 12 hydrogens, C5H12.
• There are 3 different structures, draw these below:
Displayed
formula
Structural
formula
Skeletal
formula
• All of the molecules above contain the same number of atoms but they are arranged
differently.
• They are different due to having different side groups or chains.
• This type of structural isomer is called Chain Isomerism:
1) Chain Isomerism:
These have the same molecular formula and functional group but a different
arrangement of the carbon skeleton
Example:
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Activity 2:
• Using the molymods make and draw as many molecules as possible using 3 carbons, 8
hydrogens, and 1 oxygen, C3H8O.
• Some of these structures that you have made will have different functional groups.
• There are 3 different structures, draw these below:
Displayed
formula
Structural
formula
Skeletal
formula
• All of the molecules above contain the same number of atoms but they are arranged
differently.
• 2 of these are alcohols and these show Position Isomerism
2) Position Isomerism:
These have the same molecular formula and functional group but the functional
group is attached to a different carbon
Example:
• The other molecule has a different functional group from the alcohols, (ether)
• These are called Functional group Isomerism
3) Functional group Isomerism:
These have the same molecular but the atoms are arranged into a different
functional group
Example:
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Activity 3:
• Using the molymods make and draw as many molecules as possible using 3 carbons, 6
hydrogens, and 1 oxygen, C3H6O.
• These structures will have different functional groups.
• There are 2 different structures, draw these below:
Displayed
formula
Structural
formula
Skeletal
formula
• The molecules above contain the same number of atoms but they are arranged differently.
• These molecules have a different functional group from each other.
• These are Functional group Isomerism
Example:
3) Functional group Isomerism:
These have the same molecular but the atoms are arranged into a different
functional group
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Organic reagents and their reactions:
Organic reactions
• For a reaction to occur:
A) A bond must break.
B) The breaking of a bond will form a reagent.
C) The reaction must take place
A) Bond breaking:
• For an organic reaction to occur, a covalent bond must be broken.
• Bond breaking is called fission and it can be broken in one of 2 ways:
1) Homolytic fission
• This is when the electrons in the bond go ‘HOME’ to their parent atom.
• Each atom is the same. Homo….
• A half headed arrow represents the movement of 1 electron. This is because most
reactions involve the movement of 2 electrons for which we use a normal headed arrow.
• Free radicals are atoms or groups of atoms with an unpaired electron, they are extremely
reactive and are said to be ‘short lived’.
2) Heterolytic fission
• This is when the electrons in the bond go to one of the atoms.
• A double headed arrow represents the movement of 2 electrons, a pair of electrons.
• The 2 resulting ions have a different number of electrons.
• It gives a positive ion and a negative ion.
• These are different from each other = hetero...
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B) Types of reactants:
• Reactants start a reaction going.
• There are 3 types of reactants:
1) Free radical:
These are particles with an unpaired electron, Cl.
2) Electrophile:
These are electron pair acceptors
• These are often negative ions but must have a lone pair of electrons as these are donated
to form a new covalent bond.
• Br-, OH-, H2O, NH3
3) Nucleophile:
These are electron pair donors
• These are often positive ions.
• Br2, HBr, NO2+
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C) Types of reaction:
1) Addition reactions
• Involves 2 molecules joining to become 1 molecule
• Bromine has been added to ethene.
2) Substitution reactions
• Involves an atom (or group of atoms) being replaced by another atom (or group of atoms):
• 2 molecules make 2 (new) molecules
• You can see that the Br is being substituted by OH.
3) Elimination reactions
• Involves the removal of one molecule from another.
• 1 molecule gives 2 molecules:
• Water has been eliminated from ethanol
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