1.1 What Is Organic Chemistry?

Organic chemistry is the branch of chemistry involving organic compounds. What, then, is an organic compound?

In the late 1700s, scientists defined an organic compound as one that could be obtained from a living organism, whereas inorganic compounds encompassed everything else. It was believed that organic compounds could not be made in the laboratory; instead, only living systems could summon up a mysterious “vital force” needed to synthesize them. This belief was called vitalism. By this definition, many familiar compounds, such as glucose (a sugar), testosterone (a hormone), and deoxyribonucleic acid (DNA), are organic (Fig. 1-1).

This definition of organic compounds broke down in 1828, when Friedrich Wöhler (1800–1882), a German physician and chemist, synthesized urea (an organic compound known to be a major component of mammalian urine) by heating a solution of ammonium cyanate (an inorganic compound; Equation 1-1).

An equation shows the conversion of ammonium cyanate, an inorganic compound, to urea, an organic compound, in the presence of heat. The condensed structural formula of ammonium cyanate shows a positively charged ammonium ion bonded to a negatively charged cyanate ion. When heat is applied, ammonium cyanate is converted to urea, which consists of a carbon atom bonded to two amine groups by single bonds and to an oxygen atom by a double bond.

If vitalism couldn’t account for the distinction between organic and inorganic compounds, what could? Gradually, chemists arrived at our modern definition:

An organic compound contains a substantial amount of carbon and hydrogen.

This definition, however, is still imperfect, because it leaves considerable room for interpretation. For example, many chemists would classify carbon dioxide (CO2) as inorganic because it does not contain any hydrogen atoms, whereas others would argue that it is organic because it contains carbon and is critical in living systems. In plants, it is a starting material in photosynthesis, and in animals, it is a by-product of respiration. Similarly, tetrachloromethane (carbon tetrachloride, CCl4) contains no hydrogen, but many would classify it as an organic compound. Butyllithium (C4H9Li), on the other hand, is considered by many to be inorganic, despite the fact that 13 of its 14 atoms are carbon or hydrogen. Although this definition of an organic compound has its inadequacies, it does allow chemists to classify most molecules.

Structures of glucose, testosterone and a model of DNA. The structural formula of glucose shows a linear chain of six carbon atoms. The carbon atom in the first position is bonded to an oxygen atom by a double bond and to a hydrogen atom by a single bond. The carbon atom in the third position is bonded to a hydroxyl group and a hydrogen atom by single bonds. The carbon atom in the second, fourth, and fifth positions are bonded to a hydrogen atom and a hydroxyl group each by single bonds, in reverse order to the carbon atom in the third position. The carbon atom in the sixth position is bonded to two hydrogen atoms and a hydroxyl group. The condensed structural formula of testosterone shows two cyclohexane rings fused together. The first ring is fused with a cyclohexene ring, and the second is fused with a cyclopentane ring. A double bond exists between the carbon atoms in the fourth and fifth positions. An oxygen atom is double-bonded to the carbon atom in the third position, a hydroxyl group is bonded to the carbon atom in the seventeenth position, and a methyl group is bonded to the carbon atoms in the tenth and thirteenth positions. The third illustration shows a space-filling model of the double helical structure of DNA. The caption reads, �Some familiar organic compounds: Glucose, testosterone, and DNA are organic compounds produced by living organisms.�
FIGURE 1-1 Some familiar organic compounds Glucose, testosterone, and DNA are organic compounds produced by living organisms.
Photo of a couple of aquatic snails called Bolinus brandaris, from which the dye, royal purple is obtained and the condensed structural formula of royal purple. The condensed structural formula of royal purple shows two similar structures connected by a double bond. Each of these structures consists of a hexagon ring with alternating single and double bonds inside fused with a 5-sided ring made of four carbon atoms and one nitrogen atom. The nitrogen atoms in each structure are on opposite sides of the connecting double bond, and the bromine and oxygen atoms connected to the dye also lie on opposite sides of the bond. A double bond between the carbon atoms in the second position in each structure connects them. In both the structures, double bonds exist between the carbon atoms in the 3a and fourth position, the fifth and sixth position, and the 7a and seventh position. An oxygen atom is double-bonded to the carbon atoms in the third positions, a bromine atom is bonded to the carbon atoms in the sixth positions, and the nitrogen atoms in both the 5-sided rings are each bonded to a hydrogen atom. The caption reads, Royal purple: Ancient Phoenicians processed about 10,000 aquatic snails, Bolinus brandaris, to yield 1 g of royal purple dye. The structure of the molecule responsible for the dye�s color is shown.
FIGURE 1-2 Royal purple Ancient Phoenicians processed about 10,000 aquatic snails, Bolinus brandaris (top), to yield 1 g of royal purple dye. The structure of the molecule responsible for the dye’s color is shown (bottom).

The birth of organic chemistry as a distinct field occurred around the time that vitalism was dismissed, making the discipline less than 200 years old. However, humans have taken advantage of organic reactions and the properties of organic compounds for thousands of years! Since about 6000 BC, for example, civilizations have fermented grapes to make wine. Some evidence suggests that Babylonians, as early as 2800 BC, could convert oils into soaps.

Many clothing dyes are organic compounds. Among the most notable of these dyes is royal purple, also called Tyrian purple, which was obtained by ancient Phoenicians from a type of aquatic snail called Bolinus brandaris (Fig. 1-2). These organisms produced the compound in such small amounts, however, that an estimated 10,000 of them had to be processed to obtain a single gram of dye. Therefore, the dye was available almost exclusively to those who had substantial wealth and resources—royalty.

Organic chemistry has matured tremendously since its inception. Today, we can not only use organic reactions to reproduce complex molecules found in nature, but also engineer new molecules never before seen.