Benzene is a hugely important compound in organic chemistry. It consists of six carbon atoms joined together in a ring, with a hydrogen atom bonded to each carbon; by replacing one or more of these hydrogens with a functional group, a large number of different compounds can be formed. This graphic looks at a selection of the most common simple derivatives which can be obtained in this manner.
Compounds that contain benzene rings in their structures are commonly referred to as ‘aromatic compounds’. This terminology derives from the fact that they are often have a pleasant and sweet fragrance (although benzene itself does not), but the more modern definition of the word relates to the the structure of molecules. Put simply, it refers to cyclic arrangements of bonded carbons that are conjugated – that is, they are joined by alternating double and single bonds. Whilst the criteria for a compound to be termed aromatic are a little more complicated than this, it serves as a serviceable, simple definition.
The naming of benzene derivatives can seem a little confusing to those new to organic chemistry. Unlike simpler organic molecules, which are often named in a logical, systematic manner according to the IUPAC naming rules, the names of many of the derivatives of benzene initially may not seem to follow these rules. This is due to the fact that a number of them still have ‘common’ names that are still frequently used, or even preferred, over their IUPAC names. Although it’s the systematically correct name, few organic chemists would refer to toluene as ‘methylbenzene’.
Some very important compounds that we come across on a daily basis are manufactured from derivatives of benzene. One of the most obvious is polystyrene, manufactured through the polymerisation of styrene. Polymerisation involves the reaction of many smaller molecules to form long chains of molecules. Several billion kilograms of polystyrene are produced per year, and its uses include plastic cutlery, food packaging, foam packing materials, computer housings and insulation materials.
More complex benzene-based molecules have applications in medicine; paracetamol, which has the chemical name acetaminophen, is commonly used as an analgesic to relieve pain and headaches. In fact, a large number of medicinal compounds are likely to feature a benzene ring somewhere in their structure, though these compounds are often more complicated than those shown here. In an upcoming post, we’ll actually look at some of these molecules, when we consider some of the chemical compounds behind antibiotics.
On a final note, benzene is a well known carcinogenic molecule. However, this doesn’t mean that compounds containing a benzene ring as part of their structure are also carcinogenic. It’s a common misconception that, if a compound is used to produce a certain chemical product, the risks associated with it remain the same. In fact, when benzene is reacted to produce different derivatives, it ceases to be the compound benzene, and the chemical properties of the products can often be completely different. So, the presence of a benzene ring in the structure of a compound isn’t an automatic cause for concern – in fact, a large number of compounds found in our food contain a benzene ring somewhere in their structure!
There are a lot of benzene derivatives out there – if I’ve omitted one that you think should be included in the graphic, please get in touch through the comments below!
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References & Further Reading
- Nomenclature of Benzenes – ChemWiki