In this lesson, we will learn:
• The definition of an organic compound and a hydrocarbon.
• The reason that carbon’s chemistry is studied much more than the chemistry of other elements.
• The basic rules of naming simple organic compounds.
• The different ways to draw and represent organic compounds and their features.
• Organic chemistry is chemistry to do with carbon compounds.
• Carbon atoms can make four separate bonds with any other atom(s) including other carbon atoms.
→ This makes the number of possible combinations of type of bond, number of bonds and type of atom to bond to, so large that organic chemistry has its own major area of study.
→ When chemists say ‘organic compounds’, they are talking about compounds with carbon atoms in them or compounds made of a carbon backbone – because carbon atoms bond together in long chains very frequently in nature.
• The main reason it is called organic chemistry is because many of the fundamental ‘molecules’ in living organisms are carbon compounds – including amino acids that make proteins, glucose used in respiration, and our DNA to name a few.
• Aside from living organisms, organic molecules have a wide range of uses in our day to day lives, with most coming as products of crude oil and the petroleum industry. Some products from the petrochemical industry are:
→ Gasoline/petrol fuel for cars.
→ Kerosene, fuel for aircraft.
→ Refinery gases used as fuels and as resources to make plastics.
→ Bitumen, used to tar roads.
→ ‘Naphtha’ which is a mix of organic chemicals that are used to make many cosmetics and pharmaceutical products.
• There are so many organic compounds that they are divided into categories depending on what atoms or types of bonds they contain. Amongst the simplest and most important, compounds containing only carbon and hydrogen are called hydrocarbons.
• There is a systematic way of naming organic compounds. The two most important, basic rules are below:
→ Identify the longest carbon chain in the compound. This is the core of the compound name. Depending on the carbon chain length, the following names are assigned. The table below summarizes them.
Carbon chain length:
→ Identify the functional group(s) in the compound. This will give you the suffix (end part) of the name. A few basic examples (which we’ll study in detail later) are in the table below.
→ Combining these two parts will give you the name of unbranched organic compounds – e.g. hexane (6 carbon chain, alkane), butene (4 carbon chain, alkene), ethyne (2 carbon chain, alkyne). We will learn to identify these later.
• When studying organic compounds, there are many ways to represent a chemical compound that we are talking about. Some are simpler than others, and some are more appropriate in certain situations.
→ We already know the molecular formula, which shows the chemical symbols of the atoms in the molecule and how many of these atoms there are. For example CH4 is a compound which has one carbon atom (symbol C) and four hydrogen atoms (symbol H) in each molecule.
→ The empirical formula is a shortened version of the molecular formula which shows the smallest whole-number ratio of the molecular formula. For C2H6, the empirical formula would be CH3.
→ For organic compounds we can also use the condensed formula – this is used to show the chain of carbon atoms in the compound. For example C5H12 can be written as CH3-CH2-CH2-CH2-CH3 to show the 5 carbon chain in the molecule.
→ You could also use the structural/displayed formula, which shows all the bonds between all atoms in the molecule.
→ The structural formula can be simplified by using skeletal formula – this is where a carbon atom is shown as a joint in a zig-zag chain which is the carbon backbone of the organic compound being represented. In skeletal formula, hydrogen atoms are ‘implicit’ meaning they are present but not shown in the representation. The ‘ends’ of the zig zag chains count as carbon atoms as well.
Two examples of compounds shown with each of these formulae are shown below:
Organic chemistry - Introduction
Introduction to organic chemistry
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