Chapter 1
Introduction
Organic chemistry is a branch of chemistry that studies carbon-based compounds in terms of their structure, properties, and synthesis. In contrast, inorganic chemistry covers the chemistry of all the other elements in the periodic table (Figure 1).
1. The periodic table.
This raises the question why one of the three main fields of chemistry is related purely to carbon-based compounds. One answer lies in the fact that carbon-based compounds are crucial to the chemistry of life. Indeed, the term ‘organic chemistry’ was first mooted in the 18th century by a Swedish chemist called Torbern Bergman to define the chemistry of compounds derived from living organisms. Scientists at that time believed that the chemicals of life (biochemicals) were different from those produced in the laboratory because they contained a special property that only life could provide.
To be fair, there was some justification for this belief. The biochemicals that had been identified at that time had proved difficult to isolate from living systems, and had decomposed more quickly than inorganic chemicals isolated from minerals. Therefore, it was concluded that organic compounds contained a ‘vital force’ that could only originate from a living organism. Consequently, it was logical to conclude that biochemicals could not be synthesized in the laboratory. However, it was not long before this vitalistic theory was challenged. Urea (Figure 2) is a crystalline compound that can be isolated from urine. According to vitalistic theory, it should be unique to life, but, in 1828, it was discovered that it could be synthesized by heating an inorganic salt called ammonium cyanate.
2. Synthesis of urea.
Since then, organic chemistry has come to be defined as the chemistry of carbon-based compounds, whether they originate from a living system or not. Nevertheless, the chemistry of carbon-based compounds is very much associated with the chemistry of life, and the phrase ‘carbon-based life forms’ reflects that fact. We shall be exploring the importance of organic chemistry to living systems in Chapter 4—a branch of science now defined as biochemistry.
There is another reason for considering organic chemistry as a specialist field, and that is because of the vast numbers of different organic compounds that can be synthesized—far more than would be possible for any other element. Indeed, it has been calculated that the number of different medium-sized organic molecules that could be synthesized amounts to 1063. This is a vast number, so vast that there is not sufficient carbon in the universe to achieve that goal. Note also that these figures are based on medium-sized molecules containing less than thirty carbon atoms. It ignores all the polymers that are possible. In truth, there is virtually an infinite number of novel compounds that could be synthesized, the vast majority of which have never existed on this planet. To date, 16 million compounds have been synthesized in organic chemistry laboratories across the world, with novel compounds being synthesized every day. This still represents a pinprick in the number of structures that could be synthesized. There is plenty of scope for further innovation—a fact that both excites and motivates organic chemists searching for new molecules for new purposes, whether that be in medicine, agriculture, consumer goods, or material science.
For over a hundred years, organic chemists have contributed vastly to our understanding of life at the molecular level, and produced novel compounds that have revolutionized modern society. The fruits of this research can be found in the clothes we wear, the houses we live in, and the food that we eat. The list of commodities that rely on organic chemistry include plastics, synthetic fabrics, perfumes, colourings, sweeteners, synthetic rubbers, and many other items that we use every day. It has produced the insecticides, herbicides, and fungicides that allow farmers to produce sufficient food for an ever-increasing world population, as well as the medicines that tackle disease and prolong lifespans.
The benefits have been enormous, but it is also important to appreciate the drawbacks. New discoveries can produce problems that affect health and the environment if they are not used with due care and responsibility. Unfortunately, such problems can lead to a distrust of new technology in general and chemicals in particular—an attitude that has been defined as chemophobia. The very word ‘chemical’ is considered by some to indicate a toxic or polluting compound synthesized by the chemical industry. The truth is that the word ‘chemical’ is a generic term that covers both natural and synthetic compounds. There is also a misinformed belief that synthetic compounds are inherently dangerous, whereas natural chemicals are much safer. Nothing could be further from the truth. Some of the most lethal toxins known to science come from the natural world, while many synthetic compounds are extremely safe. It is also not fully appreciated that a naturally occurring compound synthesized in the laboratory is no different from the same compound extracted from a natural source.
It is true that many of the novel compounds that were introduced for the benefit of society have produced long-term problems, but that does not mean that society should turn its back on all the medicines, pesticides, food additives, and polymers that it relies on. Instead, the challenge is to design better compounds with improved properties. It is the responsibility of organic chemists to learn from any mistakes of the past and to continue striving for the discoveries that will benefit us all. This book illustrates many of the enormous benefits that have resulted from organic chemistry research, as well as some of the problems that have arisen from past innovations. It also shows how today’s researchers are seeking a new generation of safer, more effective compounds.