Carbon – life’s framework element
Carbon is more than just another element. Of all the elements it is the only one that can form stable linkages to itself as well as to other atoms such as hydrogen and oxygen. This unique ability allows for the formation of carbon frameworks such as long chains, branched chains, rings, spheres and tubes.
How different compounds are depicted in molecular diagrams usually depends on the type of compound. There are many ways to represent molecular structures. Two popular methods are the simple ‘condensed formula’ and the ‘skeletal formula’ as illustrated in the diagram of glyceryl tristaerate below.
Glyceryl tristaerate
Glyceryl tristaerate is one of the fats found in lard, which is often used in cooking and baking. The fat is harvested from the abdominal area of a pig.
Illustrated here are 2 different ways of depicting it - on the left a skeletal formula and on the right is a condensed formula.
Organic chemistry – the chemistry of carbon
It was originally thought that all carbon compounds had their origin in living things and the name ‘organic chemistry’ was coined to show this. In 1828 Friedrich Wöhler, a German chemist, produced the organic compound urea, found in urine, from the inorganic compound ammonium cyanate.
Friedrich Wöhler
Friedrich Wöhler (1800–1882) was a German chemist, best-known for his synthesis of the organic compound urea from inorganic chemicals. He was the first to isolate several chemical elements such as aluminium.
This discovery proved the ‘origin in living things’ theory wrong but the name ‘organic chemistry’ is a convenient label and has remained to this day. Organic chemistry, then, is the study of the compounds of carbon excluding the oxides of carbon and the inorganic metal compounds known as bicarbonates, carbonates and cyanides.
Simple carbon compounds
Each carbon atom can form four linkages (bonds) to other atoms as well as itself. These linkages are stable and are known as covalent bonds. The ‘other’ atoms most commonly found are hydrogen, oxygen, nitrogen and the halogens.
Structural formulae of organic chemicals
In these 2D structural formulae of common household organic chemicals (BBQ gas, alcoholic beverages and vinegar), the single black line linking the atoms represents a single covalent bond. Each carbon has four linkages, each oxygen has two and each hydrogen has one.
for example, in these 2D structural formulae of common household organic chemicals, such as BBQ gas, alcoholic beverages and vinegar, the single black line linking the atoms represents a single covalent bond. Each carbon has four linkages, each oxygen has two and each hydrogen has one.
The condensed structural formula is a simpler representation:
Propane – CH3CH2CH3
Ethanol – CH3CH2OH
Ethanoic acid – CH3COOH
The molecular formula shows only the number and type of atom present as well as the presence of functional groups (chemically active sites):
Propane – C3H8
Ethanol – C2H5OH
Ethanoic acid – CH3COOH
The OH group is the alcohol functional group, and the COOH group is the organic acid functional group.
In addition to these formulae, 3D representations are also used that show the characteristic tetrahedral arrangement of bonds about each carbon atom.
Methane
The red sphere at the centre represents a carbon atom. The four other atoms are hydrogen, arranged in a tetrahedral pattern around the central carbon atom.
Chains and rings
Longer chains of carbon atoms can be branched and can link ‘head to tail’ fashion to form ring compounds. This ability allows for a huge variety of molecular forms, for examples isooctane (the main component in petrol) and benzoic acid (a common food preservative).
Chains and rings: Isooctane and benzoic acid
Isooctane (the main component in petrol) and benzoic acid (a common food preservative) are an example of how longer chains of carbon atoms can be branched and can link ‘head to tail’ fashion to form ring compounds.
More complex molecules
Chains and rings can fuse together in an infinite variety of ways forming structurally complex molecules.
The sex hormones testosterone and oestrogen differ in terms of structure in a very small way. However, this subtle change in structure has a huge effect on the way these hormones function in the body.
Complex molecules: Testosterone and oestrogen
The small difference in the structure of the sex hormones testosterone and oestrogen has a huge effect on the way these hormones function in the body
A study of the often structurally complex substances produced by living things can lead to the realisation that nature has a boundless imagination in terms of the design of the molecules of life. Vitamin C or ascorbic acid is an acid sugar with a ring structure. Many animals can produce vitamin C, however humans have lost this ability.
Vitamin C or ascorbic acid
Vitamin C or ascorbic acid is classified as ‘acid sugar’. It is a carbohydrate. Humans have lost the ability to produce their own ascorbic acid.
Nature of science
It is convenient to divide the study of chemistry into four branches: physical, inorganic, analytical and organic. However, to function effectively, a practising organic chemist must have a detailed knowledge and understanding of each of these branches. This is important since, nowadays, chemists tend to work as part of a team and there is a community of practice operating within the given field.
