Resource: Ringed-Carbon Compounds

Much of what we know about the chemical structures of organic compounds was revealed during the early to mid 20th century by a branch of chemistry known as "natural products chemistry." This era of chemical exploration was full of possibility for determined chemists who sought to identify, classify, and synthesize compounds produced naturally by plants and animals.

Chemists found that carbon atoms were at the foundation of all organic compounds. These atoms form strong bonds, called "covalent" bonds, in which they share electrons with other atoms. In fact, the compounds that carbon atoms form owe many of their important characteristics, such as their chemical stability and their wide variety, to these bonds. In many compounds, carbon atoms form long-chain structures. In others, they assemble in ring-shaped structures made up of four, five, or six carbon atoms bonded together. Because any one carbon atom can form as many as four single covalent bonds with other atoms, the variations in shape, size, and composition of carbon compounds is nearly limitless.

Ringed-carbon compounds were of particular interest to the natural products chemists of the early 20th century. Many of these compounds, which include alkaloids and steroids, were well known even before their chemical structures had been characterized, and their variety and the power of the physiological effects they could have on the human body were inspiring. The alkaloid family, for example, is made up of thousands of different plant compounds, many of which possess therapeutic properties. Naturally occurring steroids are involved in processes as far ranging as reproduction, development, digestion, and response to stress and injury.

Chemists have classified alkaloids and steroids based on their structural similarities. All of these compounds are based around a ringed-carbon structure. Alkaloids are composed of one or more carbon rings, each of which contains a nitrogen atom. The properties of alkaloids vary according to how many rings they contain, how those rings are assembled, and the position of nitrogen atoms within the structure.

Steroids have even more in common with one another than do alkaloids. All steroids are characterized by what chemists call the "steroid nucleus," a backbone of three six-carbon rings fused to a five-carbon ring. However, small variations in the atoms attached to the steroid nucleus can have profound effects on a steroid's properties. For example, testosterone and estrogen, the principal male and female sex hormones respectively, differ only by the presence or absence of two hydrogen atoms and one carbon atom. This small chemical difference between the two steroids effectively determines whether an individual will take on the secondary sexual characteristics of a male or a female.

To learn more about the process of synthesizing organic compounds, check out Build a Steroid and Synthesizing an Alkaloid.

• Why do you think Professor Robinson calls carbon the "Super Glue" of the chemical world?
• Why are six-atom carbon rings more stable than three- or four-atom rings?
• What makes carbon such a versatile element? What does this versatility have to do with carbon's electron configuration?
• In the cortisone molecule, oxygen is in what chemists call "position 11." How did they derive that number?