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.
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.
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.
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.
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).
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.
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.
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.