ORGANIC CHEMISTRY
Organic chemistry is often described as the chemistry of carbon-based compounds that consist primarily of carbon and hydrogen.
The unique chemistry of carbon
• Carbon atoms have the ability to form four strong covalent bonds
• Carbon undergoes a process known as hybridization which produces four available bonding sites ( see “process of hybridization”)
• Carbon atoms bond with other carbon atoms to form chains or ring structures. This is called catenation These chains can be thousands of atoms long.
• Carbon has the ability to make single, double and triple bonds with itself
Catenation is described as the ability of carbon atoms to bond with themselves to form chain or ring structures
The process of hybridisation
A carbon atom in the ground state:
A carbon atom in the “excited” state:
A process called orbital mixing now occurs where the 2s and 2p orbital’s
now mix together to produce four sub-orbitals of equal energy. There sub-
orbitals are known as sp3 hybrid orbital’s and it is these hybrid orbital’s
that provide the four available bonding sites
4 x sp3 hyhrid sub-orbitals able to accept one electron each
C
Classification of organic compounds
Alkanes C H
H
H
H C H
H
H
C
H
H
H
Alkenes C H
H
C
H
H
THE HYDROCARBONS……are organic compounds containing carbon and hydrogen only
Saturated compound – compounds in which all bonds between the carbon atoms
are single bonds.
Unsaturated compound – compounds in which there is at least one double and/or
triple bond between carbon atoms.
Homologous Series and Functional groups
C H
H
H
C
H
H
H C H
H
H
C
H
H
C H C H
H
H
C
H
H
C
H
H
C
H
H
H
H
H
H C
H
C
H
C
H
H
H C H H
H
C
H
C
H
C
H
H H C
H
C
H
H
Alkanes CnH2n+2
C2H6 C3H8 C4H10
C2H4 C3H6 C4H8
Alkenes CnH2n H
Homologous Series and Functional Groups
or…..halo group
Functional group - a bond, atom or group of atoms that form the centre of chemical
activity in the organic compound. ( also identifies to which Homologous Series an organic
compound belongs
carbon – carbon single bond
Representing organic compounds
C4H10 C4H8
Organic nomenclature
The functional group determines the suffix of the
name:
Alkanes (single bonds) end in -ane.
Alkenes (double bond) end in -ene.
ethane
ethene
Alkyl substituent – a carbon based “side chain” which
is attached to the longest continuous carbon chain in an
organic molecule.
Numerous organic molecules are found to have carbon based side chains attached to a main chain within the structure. These side chains are simply known as side branches or more scientifically correct – Alkyl Substituents
Branched hydrocarbon molecules
Straight chained hydrocarbon molecules
Naming branched chained alkanes
Naming unsaturated hydrocarbons (alkenes)
Exercise 1 : Name the following hydrocarbons
1. 2.
3. 4.
5. 6.
Memorandum
1. 2-methylbutane
2. 2,3-dimethylbutane
3. 3-ethyl-3-methylpentane
4. 3-methylbut-1-ene
5. 3,3-dimethylbut-1-ene
6. 6-methylhept-3-ene
Hydrocarbons with more than one double bond in the chain (dienes)
The rules work exactly the same in all nomenclature, the only difference is that now two positions must be stated in the naming. These positions must still be at the lowest substituted position in the molecule
For euphonic purposes, the vowel "a" must be added to the name before the suffix for dienes, e.g. buta−1,3−diene is correct, and not but−1,3−diene.
2- methylpenta -1,3 - diene 2 – methylhexa – 1,4 - diene
CH2 CH2
2-methylpent-1-ene
CH3
Haloalkanes (Alkyl halides) General formula : C Functional group = X where X = F, Cl, Br, I ( halo functional group)
The position of the halogen is specified by the lowest substituted carbon to which that halogen is attached.
Naming : The haloalkane is named with the lowest substituted carbon having the halogen attached placed first in the naming sequence
CnH2n+1X
3
Alcohols: General formula : CnH2n+1OH or CnH2n+2O
Ethanol is used widely as a solvent in paints, glues, perfumes, aftershaves and any other household products. The strong hydrogen bonds in alcohols result in alcohols having higher melting and boiling points than hydrocarbons of similar size. Functional group:
OH
Pentane -2,3 - diol
Carboxylic Acid : General formula CnH2nO2
Esters : CnH2nO2
Ester formation
Isomerism
Isomers – organic molecules which have the same molecular formula but different structural formulae.
2,2 – dimethylbutane 2 – methylpentane
There are various other types of structural isomers that can be found in organic chemistry
• Chain isomers – these are isomers that will have different chain lengths. The examples seen above
are those of chain isomers
• Positional isomers – these are isomers that have a different position of the same functional group
CH2 = CH – CH2 –CH2 – CH3 CH3 – CH = CH – CH2 – CH3
pent – 1 – ene pent – 2 – ene
• Functional isomers – isomers that contain different functional groups (eg) carboxylic acids and esters
O O
CH3 – CH2 – CH2 – CH2 – C – OH CH3 – CH2 – O – C – CH2 – CH3
pentanoic acid ethyl propanoate
C6H14
C5H10
C5H10O2
Summary of Isomerism
Exercise
CH2 – CH – CH2
O-H O-H O-H
1. 2. 3.
4. 5. 6.
7.
Memorandum 1. 1,2-dichloropropane
2. 1,1-dichloro-2,2-difluoroethane
3. Butan-2-ol
4. 2-methylbutan-2-ol
5. Propane-1,2,3-triol
6. Butyl propanoate
7. 3-methylpropa-1,2-diene
Practice Example 2
Memorandum 2
Organic Chemical Reactions Organic chemical reactions can be classified into FIVE different types of reactions based on how the molecule is able to react under certain reaction conditions • Combustion • Addition • Substitution • Elimination • Esterification - seen already
Combustion Alkanes, alkenes and alcohols burn in oxygen and form carbon dioxide and water. The reaction is exothermic and a great deal of energy is released.
Propane is the gas used in Bunsen burners in the laboratory
C3H8 + 5O2 3CO2 + 4H2O
Butane burns in oxygen
C4H10 + 6½O2 4CO2 + 5H2O
(x 2) 2C4H10 + 13O2 8CO2 + 10H2O
Ethanol burns in oxygen
C2H6O + 3O2 2CO2 + 3H2O
Addition - when a double bond is broken and new molecular fragments are added to both
Hydrogenation Halogenation
Hydrohalogenation Hydration
In the double bond, one of the bonds is very weak and will break under reaction conditions to form two unpaired electrons on each carbon. These radicals are highly reactive and will this bond to form an electron pair
ends of the bond
water (H2O) hydrohalide (HCl)
Substitution - “swapping” reactions • Halogenation (Free radical substitution) – alkanes to haloalkanes
• Hydrolysis – haloalkanes to alcohols
Elimination This is the opposite of addition where functional groups are removed to form an alkene
• Dehydrohalogenation
H H Cl H
H - C - C - C - H H - C - C = C - H + HCl
H H H H H H
• Dehydration
H H OH H
H - C - C - C - H H - C - C = C - H + H2O
H H H H H H
• Cracking - the breaking up of large hydrocarbon molecules into smaller, more useful molecules
and
Past examination Question
Memorandum