Introduction to organic chemistry

Why carbon and not silicon?


        Carbon compounds frequently contain long chains of carbon atoms


Bond energies give us the answers


E(C – C) = 347 KJMol-1

E(C – H) = 413 KJMol-1

E(C – O) = 358 KJMol-1

E(Si – Si) = 226 KJMol-1

E(Si – H) = 318 KJMol-1

E(Si – O) = 466 KJMol-1

Bonding in organic compounds:

4 bonds only A double bond and 2 single bonds to hydrogen = 4


Saturated and unsaturated hydrocarbons:


Saturated - is a hydrocarbon with single bonds only Unsaturated - is a hydrocarbon with carbon carbon multiple bonds



Aliphatic and alicyclic hydrocarbons:


Aliphatic - is a hydrocarbon in which the carbon atoms are all joined in a straight lines (branched or unbranched)
Alicyclic - is a hydrocarbon in which the carbon atoms are joined together in a ring structure



Functional groups:


Homologous series:

The Alkanes:


No of C's















5 Pentane


6 Hexane


7 Heptane


8 Octane


9 Nonane


10 Decane



Questions 1 - 3   P 103


Naming hydrocarbons

Naming organic compounds:

Carbon chain

Side chains (alkyl groups)

Functional groups


Stems, prefix and suffix:


Stem        The longest carbon chain - the main name (in the middle)    (carbon chain)

Prefix        Added before the main name - pre - main name                      (side chains)

Suffix        Added after the main name - post - main name                        (functional groups)


Alkyl groups:

Methane Methyl

No of C's





CH3 -



C2H5 -



C3H7 -



C4H9 -

5 Pentyl

C5H11 -

6 Hexyl

C6H13 -


Naming alkanes:-

1)   Look for the longest carbon chain alkane

2)   Look for the functional groups

3)   Look for the position of the functional group and assign a number.  Use the lowest number  possible counting from one end of the carbon chain.

4)   The name goes in reverse order of the 3 points above.


1)      Look for the longest straight chain alkane

The longest carbon chain is in bold.  It is 4 carbons long which makes it butane


2)      Look for the functional groups

A functional group is any side chain off the straight chain.  CH3 is a derivative of methane (CH4) which we call methyl.  See the table below


3)   Look for the position of the functional group and assign a number.  Use the lowest number possible counting from one end of the carbon chain.

Numbering from one end we get

3 – Methylbutane.  This is incorrect because if we number from the other end we get a lower number.

Numbering from the other end we get 2 – Methylbutane.  This is correct because if we get a lower number.
2 – Methylbutane  

4)      The name goes in reverse order of the 3 points above.

                                         2       -        Methyl             butane

                                         (3)                 (2)                    (1)

           5)      Additional side chains or stems 

3-ethyl 2 methyl pentane
2,2-dimethyl propane

Naming alkenes

But – 1 – ene
But – 2 – ene

Questions 1-2  P105

Naming compounds with functional groups


Functional group


Prefix (side chains)

Suffix (functional group)



C - C






C = C





– F

Floro -


– Cl

Chloro -


– Br

Bromo -


– I

Iodo -




 – OH



Hydroxy -

(if other functional groups are present)


- ol


     - CHO


- al



- one

Carboxyllic acids


- oic acid


If a suffix starts with a vowel then the stem has 'an' added


Names for alkanes containing a ring of carbon atoms




Names for Halogenoalkanes

Longest chain = 3C = prop

Functional group = Cl (prefix) = Chloroprop

Chloro is on carbon 1 = 1 chloroprop

No suffix = ane = 1 chloropropane

Names for alcohols

Longest chain = 5C = pent

Functional group =OH (suffix starts with a vowel)  = pentan   ol

OH is on carbon 3 = pentan - 3 - ol

Names for aldehydes

Longest chain = 4C = but

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. 

More than one of the same type of functional group

Longest chain = 4C = but

Functional group = Cl on carbon 1 (prefix) = 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 2 different functional groups:

Longest chain = 3C = prop

Functional group = OH on carbon 1 (suffix, starts with a vowel so add 'an') = propan - 1 - ol

Side chain = CH3 on carbon 2 (prefix) = 2 - methylpropan - 1 - ol

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

Note:  di = 2, tri = 3, tetra = 4

Question 1  P 107

Formulae of organic compounds:

Empirical formula:

                Definition:                    Empirical Formula is the simplest ratio of atoms of elements in a compound. 

Molecular formulae

                Definition:                    Molecular formulae is the actual ratio of atoms of elements in a compound.

 Recap from Module 1:

Example 1:  A sample of iron oxide was found to have 11.2g of iron and 4.8g of oxygen.  Calculate the formula of this compound:

                                           Fe                                           O

                                         11.2                                        4.8

 Divide by Ar                    11.2/56                                   4.8/16

 Moles                               0.2                                           0.3

 Divide by smallest          0.2/0.2                                    0.3/0.2

 Ratio                                1                           :                  1.5

 Ratio                                2                           :                  3


Example 2

A sample of hydrocarbon was found to have 1.20g of carbon and 0.25g of hydrogen.  Calculate the Empirical formula of this compound.  Then find out the molecular formula if the Mr = 58

                                            C                                             H

                                         1.20                                        0.25

 Divide by Ar                    1.2/12                                     0.25/1

 Moles                               0.1                                           0.25

 Divide by smallest          0.1/0.1                                    0.25/0.1

 Ratio                                1                           :                  2.5

 Ratio                                2                           :                  5

 Empirical formula                                C2H5        Mr = 29

 Molecular formula                               C4H10        58 / 29 = 2, so double up the numbers of atoms to make the actual ratio


General Formula:

            Definition:        This is the simplest algebraic formula for a member of a homologous series (of the same functional group)

Alkanes CnH2n+2   Alkenes CnH2n   Alcohols CnH2n+1OH
Methane CH4         Methanol CH3OH
Ethane C2H6   Ethene C2H4   Ethanol C2H5OH
Propane C3H8   Propene C3H6   Propanol C3H7OH


Displayed formula:


        Definition:        Shows the relative positioning of all the atoms in a molecule, and all the bonds between them


Butane:  All the atoms and bonds are shown Propan-2-ol:  Even O - H bonds are shown


Questions   1-3  P109


Structural and skeletal formula:


Structural formula:


        Definition:                shows the minimum detail for the arrangement of atoms in a molecule



1 - Chloropropane: 


This can be simplified to:                               CH3(CH2)8COOH


Skeletal formula:


        Definition:        The hydrogen's are removed leaving a carbon skeleton and associated functional groups


Other examples:


Structural formula:CH3CH2CH2CH3 Structural formula:CH3CH(CH3)CH2CH2CH3

Cyclic compounds:



Questions:  1-3  P111


Skeletal formulae and functional groups

Unsaturated hydrocarbons:

Skeletal formulae: Fill in the displayed formula:





Compounds with functional groups:


Skeletal formulae: Fill in the displayed formula:





Pentanoic acid:

Skeletal formulae: Fill in the displayed formula:



pentanoic acid  


More complex AS / A2 structures:


Retinol, vitamin A


Questions:  1-4  P113



Structural isomers: 

Activity 1:


            Definition:        These are compounds with the same molecular formula but with different structural arrangements of atoms

Activity 2:



Activity 3:

        Definition:        The same atoms are joined to each other in different spatial arrangements

E/Z Isomerism: (of which cis / trans is one type)

        1)    A carbon - carbon double bond, C=C

        2)    Each carbon must be attached to 2 different functional groups:


From GCSE:  Cis / trans - But-2-ene:


        Cis trans is a specific type based upon having a hydrogen and a non hydrogen group on each of the carbons on the C=C:


No free rotation around the C=C
Trans but-2-ene


  Cis but-2-ene


If the hydrogen's are on different sides of the ruler = TRANS = ACROSS / Trans Atlantic (across Atlantic).


If the hydrogen's are on the same side of the ruler = CIS = SAME


Cahn - Ingold - Prelog nomenclature:

If the chlorine's are on different sides of the ruler = E = 'ENTGEGEN' = OPPOSITE


If the chlorine's are on the same side of the ruler = Z = 'ZUSAMMEN' = TOGETHER

You will be expected to assign E/Z to molecules but not necessarily using CIP nomenclature


                ET = across the molecule (ET flew 'across' the galaxy!!)

Questions 1-4  P115    1-5  P143



Organic reagents and their reactions:

Organic reactions

        A)  A bond must break.

        B)  The breaking of a bond will form a reagent.

        C)  The reaction must take place


A)  Bond breaking:

        1)  Homolytic fission

        2)  Heterolytic fission

1)  Homolytic fission


Heterolytic fission

B)  Types of reactants:

        1)  Free radicals:  these have an unpaired electron and are extremely reactive (as above)

        2)  Nucleophiles:  these are attracted to electron deficient atom, d+ and donate a pair of electrons to form a new covalent bond

        3)  Electrophiles:  these are attracted to electron rich atom, d- and accept a pair of electrons to form a new covalent bond

C)  Types of reaction:


1)  Addition reactions


2)  Substitution reactions


3)  Elimination reactions