In this chapter, we first briefly review the most important types of covalent bonds encountered in organic substances and the ways in which these bonds are represented in structural formulas. Next we consider the sizes and shapes of organic molecules and how structural formulas written in two dimensions can be translated into three-dimensional models that show the relative positions of the atoms in space. We also discuss models that reflect the relative sizes of the atoms and the way in which the atoms may interfere with each other when in close quarters (steric hindrance). Then we go on to further important aspects of structure-the functional group concept and position isomerism. Our aim is to have you become more familiar with the various kinds of organic compounds and begin to see how the practicing organic chemist visualizes molecules and correlates the diverse kinds of structures that he has to deal with in his work.
- 2.1: Structural Formulas
- With few exceptions, carbon compounds can be formulated with four covalent bonds to each carbon, regardless of whether the combination is with carbon or some other element. The two-electron bond is called a single bond. Compounds in which two electrons from each of the carbon atoms are mutually shared, produce two two-electron bonds, which are called double bonds. Similarly, when three electrons from each carbon atom are mutually shared, three two-electron bonds are made, called triple bonds.
- 2.2: The Sizes and Shapes of Organic Molecules
- The size and shape of molecules are as much a part of molecular structure as is the order in which the component atoms are bonded. Contrary to the impression you may get from structural formulas, complex molecules are not flat and formless, but have well-defined spatial arrangements that are determined by the lengths and directional character of their chemical bonds. Mechanical model are useful that address molecular geometry, including approximations of relative bond lengths and orientation.
- 2.3: Classification by Functional Groups
- There are a number of recurring types of structural features in organic compounds that commonly are known as functional groups. In fact, a traditional approach to the subject of organic chemistry involves the classification of compounds according to their functional groups. It will be helpful to look at the structural features of some of the major types of organic compounds even though the details of their chemistry will not be discussed until later chapters.
- 2.4: Isomerization in Organic Compounds
- More than one stable substance can correspond to a given molecular formula. Compounds having the same number and kinds of atoms are called isomers. Compounds having the same number and kind of atoms but having different bonding arrangements between the atoms are called position isomers.
- 2.E: Structural Organic Chemistry (Exercises)
- These are the homework exercises to accompany Chapter 2 of the Textmap for Basic Principles of Organic Chemistry (Roberts and Caserio).
Contributors and Attributions
John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."