Organic Chemistry: Concepts and Applications - Headley Allan D. 2020

Bonding and Structure of Organic Compounds
1.1 Introduction

The word “organic” was first used to describe compounds that were derived from plants or animals, but this term was later used to describe compounds that contain mostly carbon and hydrogen atoms. Today, the term organic is loosely used to describe food that is produced without the use of pesticides, hormones, antibiotics, or fertilizers.

In organic chemistry, we will carry out a detailed study of the composition, properties, and reactions of compounds that contain primarily carbon and hydrogen atoms, also known as organic compounds. Even though many organic compounds contain only carbon and hydrogen atoms, a large percentage contains other atoms, such as oxygen, nitrogen, sulfur, as well as halogens; these atoms are referred to as heteroatoms. Atoms other than carbon and hydrogen that are present in organic compounds are called heteroatoms.

Prior to the start of the nineteenth century, chemists were familiar with inorganic compounds; for example, it was known that ammonium cyanate, an inorganic compound, could be easily made by the exchange reaction shown in Reaction (1-1).

(1-1)

Even though organic compounds were known, similar reactions that could be used for their synthesis were not known. Instead, organic compounds were obtained primarily from natural sources, such as extraction from plants and other natural sources. As early as 1828, a medical doctor, Friedrich Wöhler, synthesized urea, a known organic compound. The synthesis of urea was accomplished by heating ammonium cyanate (an inorganic compound), as shown by the reaction in Reaction (1-2).

(1-2)

This was a major discovery that initiated the era of organic chemistry. For the first time, an organic compound could be synthesized and these types of compounds did not have to be obtained naturally. In the early 1800s, just about all compounds that were used for different reasons, mostly medical, were obtained from natural sources. Today, a large percentage of organic compounds, including urea, which is a major component of fertilizer, adhesives, and resins, are synthesized and are not obtained naturally.

DID YOU KNOW?

Fruits and vegetables that are produced without the use of pesticides or fertilizers are described as “organic.”

Organic chemistry is that branch of science that deals with the synthesis and properties of compounds that contain primarily carbon and hydrogen atoms. As mentioned earlier, many other compounds that also contain heteroatoms are also considered organic. It is truly remarkable that the millions of known organic compounds, with new ones being constantly synthesized, all contain only carbons, hydrogens, and just a few heteroatoms! Today, most of the organic compounds that are synthesized are not made from inorganic compounds, but from simpler organic compounds. Some known everyday organic compounds that are made from simple starting organic compounds are shown below.

You may be wondering where are the carbon and hydrogen atoms in these compounds since they are not shown in the structure, except for the first structure, which shows two representations of N,N-diethyl-3-methylbenzamide (DEET). You will learn later in this chapter that at each intersection in the structure, there are carbon and hydrogen atoms or just carbon atoms. DEET contains carbon, hydrogen, oxygen, and nitrogen atoms. Ibuprofen, a painkiller, contains carbon, hydrogen, and oxygen atoms. The artificial sweetener, saccharin, contains carbon, hydrogen, oxygen, nitrogen, and sulfur atoms. Dichlorodiphenyltrichloroethane (DDT), which is used as an insecticide, contains carbon, hydrogen, and chlorine atoms. As mentioned earlier, these compounds are still considered organic even though they contain heteroatoms and not just carbon and hydrogen atoms. Today, a variety of useful organic compounds, like those shown above, are made from simple starting compounds and they are not obtained from natural sources. Various drugs, pesticides, herbicides, plastic bottles, and various household cleaners are examples of compounds that are synthesized from simple starting compounds. A specific branch of chemistry that deals with the synthesis of such compounds from simple starting compounds is called organic synthesis. Today’s pharmaceutical industries routinely synthesize important drugs to cure various diseases, but there are many factors that must be considered before a decision is made to synthesize a particular drug or to isolate it from nature as was typically done in the 1800s as pointed out earlier. It is extremely expensive to develop a particular drug, and isolation from natural sources has environmental impacts that must be considered.

DID YOU KNOW?

Taxol is an organic compound that is used for the cure of cancer, specifically cervical and breast cancer.

When taxol was first discovered as a possible cure for cancer, its primary source was from the dried inner bark of the Pacific Yew tree. Taxol is only about 0.02% by weight of the Pacific Yew tree. This means that in order to produce approximately 1 kg of the drug, it would require at least 5000 kg of bark from approximately 2500 trees. Thus, a requirement of about 2 g of taxol for each treatment would result in the reduction or loss of a number of these trees. Since the Pacific Yew tree is a slow-growing evergreen tree, it is obvious that obtaining taxol for medicinal purpose would have a tremendous environmental impact and perhaps lead to the extinction of Pacific Yew trees. Fortunately, organic chemistry allows taxol to be synthesized from simpler starting compounds, but its synthesis involves a time-consuming and costly process.