Organic chemistry
Organic chemistry is the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives. These compounds may contain any number of other elements, including hydrogen, nitrogen, oxygen, the halogens as well as phosphorus, silicon, and sulphur. Organic compounds are structurally diverse.
The range of application of organic compounds is enormous. They either form the basis of, or are important constituents of many products including plastics, drugs, petrochemicals, food, explosives and paints. They form the basis of almost all earthly life processes (with very few exceptions).
Inorganic Chemistry
Inorganic Chemistry is the study of the structure, properties, and reactions of the chemical elements and their compounds. Inorganic chemistry does not include the investigation of hydrocarbons (compounds composed of carbon and hydrogen).
ORGANIC AND INORGANIC COMPOUNDS
Organic compounds
Organic compounds can be defined as compounds which contain hydrocarbon. Organic compounds are classified as natural or artificial. The physical structures of all living things are composed mainly of organic compound.
Examples of natural organic compounds
1. Carbohydrates
2. Protein
3. Vitamins
4. Enzymes
5. Hormones
6. Herbs
7. Fats and oils
Examples of artificial organic compounds
1. Plastic
2. Insecticides
3. Pesticides
4. Soap
5. Dyes
6. Drugs etc.
Characteristics of organic compounds
1. Carbon can forms four bonds and is described as tetravalent.
2. Carbon can form a ring or cyclic compounds.
3. Carbon can bond with other atoms to form stable compounds.
4. Carbon atoms can combine with each other and hydrogen atom to form open, straight and branched chains.
5. Carbon can bond with another carbon atom through stable, double and triple bonds. No other atom can form stable multiple bonds.
6. Organic compounds have low melting and boiling points
7. They occur in all the states of matter (liquid, gas and solid).
8. They are highly volatile. Inorganic compounds Inorganic compounds are compounds which do not contain hydrocarbons.
Examples of inorganic compounds
1. Chalk
2. Salt
3. Washing soda
4. Carbon monoxide, CO
5. Carbon dioxide, CO2
6. Trioxocarbonate (IV), CO3 2-
Characteristics of inorganic compounds
1. They are mostly ionic.
2. They are insoluble in organic solvents.
3. They have quick rate of reaction.
4. They are not volatile.
5. They have high melting and boiling points.
Differences between organic and inorganic compounds
Organic compounds Inorganic compounds
1. Mostly covalent Mostly ionic
2. Have low boiling and melting points Have high boiling and melting points
3. Generally soluble in organic solvents Generally insoluble in organic solvents
4. Slow reaction rate Fast reaction rate
5. Highly volatile Normally not volatile
Types or families of organic compounds
Organic compounds are divided into families known collectively as homologous series.
Homologous series is a group of organic compounds made up of a series of compounds in which all members can be represented by the same general formula but different structural formulas.
Properties of the homologous series
1. They can be represented by a general formula.
2. They possess different structural formulas.
3. They can be prepared by a general method.
4. They have similar chemical properties because they have the same general formula.
5. They have different physical properties.
Types of organic compounds
Hydrocarbons
Alkanol
Alkanoic acids
Alkanoates
Fats and oils.
Functional groups
Functional groups are atoms or group of atoms or bonds which give a family of organic compounds it characteristic chemical properties.
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A functional group does not exist independently but forms a part of a molecule. The properties of any family of organic compound in the homologous series depend on the functional group as well as the nature of the carbon chain.
Hydrocarbons
Hydrocarbons are organic compounds, composed entirely of carbon and hydrogen. They are the organic compounds of simplest composition and may be considered the parent substances from which all other organic compounds are derived.
Types of hydrocarbons
Hydrocarbons are conveniently classified into two major groups, open-chain and cyclic.
Open-chain hydrocarbons
In open-chain compounds containing more than one carbon atom, the carbon atoms are attached to each other to form an open chain; the chain may carry one or more side branches. They are made up of aliphatic compounds such as alkanes, alkenes and alkynes which are hydrocarbons with single, double and triple bonds respectively.
Cyclic compounds
In cyclic compounds the carbon atoms form one or more closed rings as in aromatic compounds. The two major groups are subdivided according to chemical behaviour into saturated and unsaturated compounds.
Saturated hydrocarbons: These are those compounds which contain hydrogen and carbon atoms only, with single covalent bonds. Alkanes are saturated hydrocarbons. Petroleum contains a great variety of saturated hydrocarbons, and petroleum products such as gasoline, kerosene, heavy fuel oil, lubricating oils, petroleum jelly, and paraffin consist principally of mixtures of paraffin hydrocarbons, which range from the lighter liquid members to the solid members.
Unsaturated hydrocarbons: These are those with double and triple covalent bonds. Alkenes and alkynes are unsaturated hydrocarbons. Alkanes These are single-bonded hydrocarbons, containing carbon atoms surrounded by a maximum of four hydrogen ions. Alkanes have the general formula CnH2n+2, where n is the number of carbon atoms in the molecule.
The structure and naming of alkanes
Hydrocarbons are named based on the number of carbon atoms contained in the molecule.
If the molecule contains only one carbon atom, it is prefixed meth-;
if there are two carbon atoms, it is prefixed eth- and if the molecule contains ten carbon atoms, it is prefixed dec-.
Each of the members of alkane is suffixed with –ane.
Among the members of the series are methane CH4; ethane, C2H6; propane, C3H8; and butane, C4H10.
There are two ways of writing a condensed structural formula. For example, butane may be written as: CH3CH2CH2CH3 or CH3(CH2)2CH3.
The members of alkane, their molecular and structural formulas
Alkane Name Molecular Formula
Structural Formula
1 Methane CH4 CH4
2 Ethane C2H6 CH3CH3
3 Propane C3H8 CH3CH2CH3
4 Butane C4H10 CH3CH2CH2CH3
5 Pentane C5H12 CH3CH2CH2CH2CH3
6 Hexane C6H14 CH3(CH2)4CH3
7 Heptane C7H16 CH3(CH2)5CH3
8 Octane C8H18 CH3(CH2)6CH3
9 Nonane C9H20 CH3(CH2)7CH3
10 Decane C10H22 CH3(CH2)8CH3
Properties of alkanes
Physical properties
1. The first four members of the series are gases at ordinary temperature and pressure
2. Intermediate members are liquids; and the heavier members are semi-solids or solids.
3. Alkanes are insoluble in water.
4. They are soluble in non-polar solvents such as ether and benzene.
5. They are colourless.
Chemical properties
1. Alkanes are unreactive; that is, they do not react readily at ordinary temperatures with such reagents as acids, alkalies, or oxidizers.
2. They undergo reaction in the presence of excess oxygen to give carbon dioxide and water. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
3. They react in limited supply of oxygen to give carbon monoxide. 2CH4(g) + 3O2(g) → 2CO(g) + 4H2O(g)
4. Alkanes react with halogens in the presence of sunlight to give haloalkanes and the corresponding halide. Methane, for example, reacts with chlorine to give chloromethane and hydrogen chloride. CH4(g) + Cl2(g) → CH3Cl(g) + HCl(g) Sources of alkanes petroleum (crude oil) natural gas plants and animal remains and wastes
Uses of alkanes
1. Alkanes are used mostly as sources of fuels either domestically or industrially.
2. Methane, for instance, is used in the house for cooking
3. Butane is used in lighters.
4. Higher alkanes such as octane are used in petrol and other fuels.
Alkenes
Alkenes, also known as olefins, are formed when an alkane misses two hydrogen atoms to form a carbon-carbon double bond (C=C) Alkenes have the general formula CnH2n.
The structure and naming of alkenes
Alkenes have the same prefixes as alkanes, but are suffixed –ene instead of -ane.
If the molecule contains two carbon atoms (C2), for example, it is called ethene (C2H4);
If there are three carbon atoms – propene (C3H6)
If there are ten carbon atoms – decene (C10H20).
Properties of alkenes
Physical properties
1. Alkenes have relatively low boiling and melting points than alkanes.
2. They are insoluble in water.
3. They are soluble in certain non-polar organic solvents such as petroleum.
4. At normal temperature and pressure, the first four members are gases, the middle members, liquids and the last members are semi-solids and solids.
Chemical properties
1. Alkenes react with water to give alkanol (alcohol). C2H4 + H2O → C2H5OH
2. They undergo additional reaction with hydrogen, halogens and bromine water. For example, they undergo hydrogenation with hydrogen in the presence of Pb, Ni or Pt catalyst to give the corresponding alkane. C2H4 + H2 → C2H6
3. Alkenes react with excess oxygen to produce carbon dioxide and water. C2H4 + 3O2 → 3O2 + 2H2O
4. Alkenes can undergo self addition reaction to form large molecules under high temperature and pressure in a process known as polymerisation. For example, ethene can polymerise to produce low-density polyethene.
Uses of alkenes
1. Ethene is used to manufacture
detergents.
2. It is used to manufacture plastics.
3. It is used in the process of fruit ripening.
4. It is used in the industrial preparation of ethanol.
5. It is used in the manufacture of glycerol.
6. Propene is used to make polypropene.
7. It is used to make synthetics fibres and Buna-n-rubber.
Alkynes
Alkynes are triple-bonded (-C≡C-) hydrocarbons with the general formula C2H2n-2. Where n is the number carbon atoms present in the molecule.
Structure and naming of alkynes
Just like alkanes and alkene, alkynes are named based on the corresponding number of carbon atoms in the molecule, with the ethanol (C2H5OH), propanol (C3H7OH) etc.
Examples of alkanols
1. methanol
2. ethanol
3. propanol
4. butanol
Properties of alkanols
Physical properties
1. Alkanols are generally soluble in water.
2. They are colourless.
3. They are mostly liquids or gases at room temperature.
4. Ethanol has a boiling point of 78oC and freezes at -114oC.
Chemical properties
1. Alkanols burn in air to produce carbon dioxide and water. C2H5OH + 3O2 2CO2 + 3H2O
2. They undergo dehydration in the presence of concentrated H2SO4 to produce the corresponding alkene and water. C2H5OH C2H4 + H2O
3. They react with carboxylic acids to produce esters and water in a reversible reaction called esterification reaction.
4. They are oxidized to acids with acidified potassium dichromate. C3H7 (with K2C2O7 H) C3H5OOH
Uses of alkanols
1. Alkanols are used for sterilizing instruments.
2. They are used as fuels.
3. They are used as solvents for paints, vanish, stains etc.
4. They are used to prepare alcoholic beverages such as wines, beers, spirits etc.
5. alkanols (95% ethanol and 5% methanol) are used in the preparation of industrial methylated spirit.
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