Introduction to Organic Chemistry

1
Introduction to Organic Chemistry
2
Contents

• Nomenclature and Isomerism
• Petroleum and Alkanes
• Alkenes and Epoxyethane
• Haloalkanes
• Alcohols

3
Nomenclature and Isomerism

• The study of the compound of carbon is called
  organic chemistry.
• Groups of carbon compounds with the same
  functional group are called homologous series
• Organic compounds are named according to their
  longest carbon chain.

4
Nomenclature
5
Isomerisation

• Both of the following have four carbon atoms and
  ten hydrogen atoms they are called isomers

Butane
2-Methyl propane

• The number 2 indicates that the methyl group is
  attached to the second carbon.
• Carbons are always number so that the lowest
  numbers appear in the name.
• This type of isomerism is called structural
  isomerism
• Positional isomers have functional groups at
  different positions along the chain
• Functional group isomers have different
  functional groups but have the same molecular
  formulae, such as acids and esters

6
Petroleum and Alkanes

• Petroleum
• Combustion
• Pollution

7
Petroleum

• Petroleum is another name for crude oil, it is a
  mixture of hydrocarbons.
• The hydrocarbons in crude oil all have different
  boiling points, this property allows them to be
  separated by a process call fractional
  distillation.
• Fractional distillation produces more long chain
  hydrocarbons than the market requires. They are
  made into shorter more useful molecules by a
  process called cracking.
• Thermal cracking splits the bonds in the
  hydrocarbon by a free radical process this uses a
  lot of energy because of the high temperatures
  used.
• Zeolite catalysts can be used to lower the
  temperature of the cracking process. It proceeds
  via ionic intermediates.

8
Combustion

• In excess oxygen alkanes burn according to the
  following equation
• CnH2n2 (1.5n0.5)O2 ? nCO2 (n1)H2O
• This is called complete combustion, however if
  there is in sufficient oxygen present incomplete
  combustion can occur.
• CnH2n2 (n0.5)O2 ? nCO (n1)H2O
• With even less oxygen soot is formed.

9
Pollution

• Many pollutants are formed by the combustion of
  fossil fuels. These include soot and carbon
  monoxide formed by the incomplete combustion of
  hydrocarbons.
• Besides making every thing look dirty carbon
  particulates in the atmosphere cause breathing
  problems in those who are susceptible.
• Carbon monoxide interferes with the bloods
  ability to carry oxygen and in severe case can
  lead to death.
• Other harmful gases include
• sulphur dioxide which is formed by the oxidation
  of impurities in fossil fuels
• and nitrogen oxides which are formed atmospheric
  nitrogen is oxidised during the combustion
  process.
• Both of these species react with rain water to
  form acid rain.

10
Alkenes and Epoxyethane

• Alkenes are unsaturated. This means that they do
  not have the maximum possible number of hydrogen
  atoms.
• The double bond in in alkenes is comprised of a
  covalent bond and a pi bond. The pi bond has
  electron density above and below the covalent
  bond and is weaker than a covalent bond.
• Because of the weaker second bond alkenes are
  more reactive than alkanes.
• There is no rotation around the double bond, this
  causes alkenes to have a planar shape.

11
Reactions of Alkenes
H2 catalyst Heat pressure
n
steam catalyst
Catalyst heat
Remember in the presence of alkenes bromine
water decolourises
HCl
Br2
12
Epoxyethane
O
CH2
CH2

• Epoxyethane is produced from ethene and air or
  oxygen in the presence of a silver catalyst.
• The 3-membered ring is strained and results in
  high reactivity.
• Epoxyethane is industrially important because it
  is hydrolysed to produce ethane-1,2 diol which is
  then used in the production of antifreeze and
  polyesters.

13
Haloalkanes

• Haloalkanes contain polar bonds. This is because
  the halogen is more electronegative than the
  carbon.
• This results in the carbon atom being slightly
  positive and attractive to electron rich species.
• Reactions resulting from this type of attraction
  are called nucleophilic substitution.

The carbon atom of the CN- ion donates a pair of
electrons to the haloalkane and the C Br breaks
with loss of a bromide ion. A new C CN bond is
formed.
d-
d
CN-
C
Br
14
Elimination

• On heating bromoethane with a strong base
  dissolved in ethanol, hydrogen bromide is
  eliminated and ethene is formed
• CH3CH2Br CH2CH2 HBr

• KOH/ethanol

15
Alcohols
Primary
Secondary
Tertiary Alcohols are classified according to
the number of carbon atoms bonded to the carbon
atom adjacent to the OH group.
16
Manufacture of Alcohols

• Alcohol for human consumption is produced by
  natural fermentation. Yeasts produce enzymes
  which catalyse the reaction called zymases.
• Industrially it cheaper to form ethanol for
  solvent by the hydrolysis of ethene.
• It is cheaper to obtain ethanol in this manner
  because it is produced in a continuous process

17
Reactions of Alcohols

• Oxidation of primary alcohols produces an
  aldehyde.
• Aldehydes produce a silver mirror with Tollens
  reagent
• Secondary and tertiary alcohols produce ketones
  upon oxidation these do not give a silver mirror
  with ketones.
• Heating alcohols with sulphuric or phosphoric
  acid causes them to eliminate water and produce
  alkenes

18
Summary

• Nomenclature and Isomerism
• Naming of organic compounds is systematic it
  depends on chain length and functional groups it
  allows us to identify isomers
• Petroleum and Alkanes
• Most of our hydrocarbon come from crude oil, they
  are used extensively for fuel. But this can cause
  environmental problems
• Alkenes and Epoxyethane
• Alkenes have a double bond which makes them much
  more reactive. They are a useful feedstock for
  the plastics industry
• Haloalkanes
• These molecules have polar bonds which results in
  them being susceptible to nucleophilic attack.
• Alcohols
• The reaction of this series of compound depend on
  whether they are primary, secondary or tertiary.
  He primary being much more readily oxidised than
  the others.