Nomenclature and Isomerism Study Guide (page 2)
Organic chemistry is the study of the structure and reactivity of compounds containing carbon. Carbon is the backbone of more compounds than all other elements combined. The strength of the carbon-carbon bond allows for an infinite number of possible compounds and infinite possibilities for the discovery of new and exciting drugs, plastics, and other innovations.
As stated, organic chemistry is the study of compounds containing carbon. In other words, organic chemistry is the study of life, because carbon compounds are essential to biological processes. Most organic compounds also contain hydrogen (hydrocarbons), and many contain heteroatoms such as oxygen, nitrogen, the halogens, phosphorus, and sulfur. Nucleic acids (DNA, RNA, etc.), proteins, carbohydrates (sugars), fats (lipids), plastics, and petroleum products are just a few classes of organic compounds.
Organic chemistry can be traced back to the nineteenth century when German chemist Friedrich Wöhler discovered that urea, a component of urine, was organic:
Carbon is tetravalent (forming four bonds) and can form single bonds, double bonds, and triple bonds. As seen in Table 12.1, the four types of hydrocarbons are alkanes (single bonds), alkenes (double bonds), alkynes (triple bonds), and aromatic. Aromatics are unsaturated hydrocarbons that have cyclic structures. A common and representative compound for aromatic is benzene.
Nomenclature of Alkanes
Alkanes are organic molecules in which all the carbons are bonded to four atoms (i.e., all single bonds). These molecules are saturated because carbon has the maximum number of atoms surrounding it. Organic molecules are named systematically using a straight-chain or unbranched alkane as a backbone (see Table 12.2).
Rules for naming alkanes:
Give the IUPAC systematic name for the following molecules:
Locate the longest chain:
Locate the substituents:
Number the chain using the lowest numbers:
Name the molecule:
Isomers are defined as different compounds with the same molecular formula. 2-Methylbutane has two other isomers with the molecular formula C5H12. Each compound must have a unique systematic name. Because molecules can be drawn many different ways, a name can confirm whether the molecule with the same molecular formula is an isomer or the same molecule drawn differently.
Some of the ways to draw 2-methylbutane (i.e., the same molecule drawn differently) are as follows:
Alkenes and Alkynes
The nomenclature of alkenes and alkynes follows the same rules as alkanes, except the double or triple bond must be numbered. The multiple bond is numbered on the first number to which it is assigned. Also, because double bonds have a rigid configuration, they can exhibit a cis or trans isomerism. A cis structure is one with substituents on the same side of the double bond, and the trans is one with the substituents are on opposite sides of the double bond.
Name the following molecules:
Stereoisomers are isomers with the same connectivity but a different three-dimensional structure. Your hands are stereoisomers, mirror images but nonsuperimposable. They have the same connectivity, but you cannot put your left glove on your right hand. Bromochloroiodomethane is one of the simplest molecular models. Notice that the carbon atom has four different groups attached, which is called a stereocenter or stereogenic carbon.
So far, only hydrocarbons have been discussed in this lesson. Oxygen, nitrogen, and the halogens are elements commonly found in organic molecules. The exact bonding and arrangement of these elements in compounds are functional groups (see Table 12.3). The functional group of an organic compound determines the specific physical and chemical properties. For example, most esters have a fruity fragrance, most haloalkanes have a density greater than 1 (the density of water), and alcohol reacts readily with alkali metals.
Identify the functional groups in phenylalanine (an amino acid and component of aspartame and proteins) and vanillin (vanilla scent):
Practice problems for these concepts can be found at - Nomenclature and Isomerism Practice Questions
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