• Organic chemistry is the branch of chemistry that deals with organic molecules. An organic molecule is one that contains carbon.
• All living organisms contain carbon. Plants use sunlight to convert carbon dioxide in the air into organic compounds through the process of photosynthesis. Animals and other organisms then feed on plants to obtain their own organic compounds. Fossil fuels are another important source of carbon.
• It is the unique properties of the carbon atom that give organic compounds certain properties.
• The carbon atom has four valence electrons, so it can bond with many other atoms, often resulting in long chain structures. It also forms mostly covalent bonds with the atoms that it bonds to, meaning that most organic molecules are non-polar.
• An organic compound can be represented in different ways, using its molecular formula, structural formula or condensed structural formula.
• If two compounds are isomers, it means that they have the same molecular formulae but different structural formulae.
• A functional group is a particular group of atoms within a molecule, which give it certain reaction characteristics. Organic compounds can be grouped according to their functional group.
• The hydrocarbons are organic compounds that contain only carbon and hydrogen. They can be further divided into the alkanes, alkenes and alkynes, based on the type of bonds between the carbon atoms.
• The alkanes have only single bonds between their carbon atoms and are unreactive. • The alkenes have at least one double bond between two of their carbon atoms. They
are more reactive than the alkanes.
• The alkynes have at least one triple bond between two of their carbon atoms. They are the most reactive of the three groups.
• A hydrocarbon is said to be saturated if it contains the maximum possible number of hydrogen atoms for that molecule. The alkanes are all saturated compounds.
• A hydrocarbon is unsaturated if it does not contain the maximum number of hydrogen atoms for that molecule. The alkenes and alkynes are examples of unsaturated molecules. If a double or triple bond is broken, more hydrogen atoms can be added to the molecule. • There are three types of reactions that occur in the alkanes: substitution, elimination
and oxidation reactions.
• Organic compounds are named according to their functional group and its position in the molecule, the number of carbon atoms in the molecule and the position of any double and triple bonds. The IUPAC rules for nomenclature are used in the naming of organic molecules.
• Many of the properties of the hydrocarbons are determined by their molecular structure, the bonds between atoms and molecules, and their surface area.
• The melting point and boiling point of the hydrocarbons increases as their number of carbon atoms increases.
• The molecular mass of the hydrocarbons determines whether they will be in the gaseous, liquid or solid phase at certain temperatures.
• An alcohol is an organic compound that contains a hydroxyl group (-OH).
• The alcohols have a number of different uses including their use as a solvent, for medicinal purposes and in alcoholic drinks.
• The alcohols share a number of properties because of the hydroxyl group. The hydroxyl group affects the solubility of the alcohols. Those with shorter carbon chains are generally more soluble, and those with longer chains are less soluble. The strong hydrogen bond between the hydrogen and oxygen atoms in the hydroxyl group gives alcohols a higher melting point and boiling point than other organic compounds. The hydroxyl group also gives the alcohols both acidic and basic properties.
• The carboxylic acids are organic acids that contain a carboxyl group with the formula -COOH. In a carboxyl group, an oxygen atom is double-bonded to a carbon atom, which is also bonded to a hydroxyl group.
• The carboxylic acids have weak acidic properties because the hydrogen atom is able to dissociate from the carboxyl group.
• An ester is formed when an alcohol reacts with a carboxylic acid.
• The amines are organic compounds that contain an amino functional group, which has the formula -NH2. Some amines belong to the amino acid group, which are the building
blocks of proteins.
• The ketones are a group of compounds that contain a carbonyl group, which consists of an oxygen atom that is double-bonded to a carbon atom. In a ketone, the carbonyl group is on the end of the carbon chain.
Exercise: Summary exercise
1. Give one word for each of the following descriptions:
(a) The group of hydrocarbons to which 2-methyl-propene belongs. (b) The name of the functional group that gives alcohols their properties. (c) The group of organic compounds that have acidic properties.
(d) The name of the organic compound that is found in vinegar.
(e) The name of the organic compound that is found in alcoholic beverages. 2. In each of the following questions, choose the one correct answer from the
list provided.
(a) When 1-propanol is oxidised by acidified potassium permanganate, the possible product formed is...
i. propane ii. propanoic acid iii. methyl propanol iv. propyl methanoate
(IEB 2004)
(b) What is the IUPAC name for the compound represented by the following structural formula? H C Cl H C Cl Cl C H C H H H H i. 1,2,2-trichlorobutane ii. 1-chloro-2,2-dichlorobutane iii. 1,2,2-trichloro-3-methylpropane iv. 1-chloro-2,2-dichloro-3-methylpropane (IEB 2003)
3. Write balanced equations for the following reactions: (a) Ethene reacts with bromine
(b) Ethyne gas burns in an excess of oxygen (c) Ethanoic acid ionises in water
4. The table below gives the boiling point of ten organic compounds. Compound Formula Boiling Point (0C)
1 methane CH4 -164 2 ethane C2H6 -88 3 propane C3H8 -42 4 butane C4H10 0 5 pentane C5H12 36 6 methanol CH3OH 65 7 ethanol C2H5OH 78 8 propan-1-ol C3H7OH 98 9 propan-1,2-diol CH3CHOHCH2OH 189 10 propan-1,2,3-triol CH2OHCHOHCH2OH 290
The following questions refer to the compounds shown in the above table. (a) To which homologous series do the following compounds belong?
i. Compounds 1,2 and 3 ii. Compounds 6,7 and 8
(b) Which of the above compounds are gases at room temperature?
(c) What causes the trend of increasing boiling points of compounds 1 to 5? (d) Despite the fact that the length of the carbon chain in compounds 8,9
and 10 is the same, the boiling point of propan-1,2,3-triol is much higher than the boiling point of propan-1-ol. What is responsible for this large difference in boiling point?
(e) Give the IUPAC name and the structural formula of an isomer of butane. (f) Which one of the above substances is used as a reactant in the preparation
of the ester ethylmethanoate?
(g) Using structural formulae, write an equation for the reaction which pro- duces ethylmethanoate.
(IEB 2004 )
5. Refer to the numbered diagrams below and then answer the questions that follow.
HO C C C C H O H H H H H H 1 HO C C H H H H H 2 H C C C C H H Br H Br 3 H C C O C H H O H H 4 H
(a) Which one of the above compounds is produced from the fermentation of starches and sugars in plant matter?
i. compound 1 ii. compound 2 iii. compound 3 iv. compound 4
(b) To which one of the following homologous series does compound 1 belong? i. esters
ii. alcohols iii. aldehydes iv. carboxylic acids
(c) The correct IUPAC name for compound 3 is... i. 1,1-dibromo-3-butyne
ii. 4,4-dibromo-1-butyne iii. 2,4-dibromo-1-butyne iv. 4,4-dibromo-1-propyne
(d) What is the correct IUPAC name for compound 4? i. propanoic acid
ii. ethylmethanoate iii. methylethanoate iv. methylpropanoate IEB 2005
6. Answer the following questions: (a) What is a homologous series?
(b) A mixture of ethanoic acid and methanol is warmed in the presence of concentrated sulphuric acid.
i. Using structural formulae, give an equation for the reaction which takes place.
ii. What is the IUPAC name of the organic compound formed in this reaction?
H C C C C H
H H H
H H
i. Give the IUPAC name for this compound.
ii. Give the balanced equation for the combustion of this compound in excess oxygen.
(IEB Paper 2, 2003)
7. Consider the organic compounds labelled A to E. A. CH3CH2CH2CH2CH2CH3 B. C6H6 C. CH3-Cl D. Methylamine H C C C C C H H H C H H H C H H C H H H H H O H H H E
(a) Write a balanced chemical equation for the preparation of compound C using an alkane as one of the reactants.
(b) Write down the IUPAC name for compound E.
(c) Write down the structural formula of an isomer of compound A that has only FOUR carbon atoms in the longest chain.
Chapter 2
Organic Macromolecules - Grade
12
As its name suggests, a macromolecule is a large molecule that forms when lots of smaller molecules are joined together. In this chapter, we will be taking a closer look at the structure and properties of different macromolecules, and at how they form.