# 4: Alkanes

Alkanes are the simplest organic molecules, consisting of only carbon and hydrogen and with only single bonds between carbon atoms. Alkanes are used as the basis for naming the majority of organic compounds (their nomenclature). Alkanes have the general formula $$C_nH_{2n+2}$$.

• 4.1: Prelude to Alkanes
Although this chapter is concerned with the chemistry of only one class of compounds: alkanes, several fundamental principles are developed that we shall use extensively in later chapters. The study of some of these principles has been associated traditionally more with physical chemistry than with organic chemistry. We include them here, at the beginning of out discussion of organic reactions, because they provide a sound basis for understanding the practical use of organic reactions.
• 4.2: Physical Properties of Alkanes and The Concept of Homology
The series of straight-chain alkanes, in which n is the number of carbons in the chain, shows a remarkably smooth gradation of physical properties. As n increases, each additional $$CH_2$$ group contributes a fairly constant increment to the boiling point and density, and to a lesser extent to the melting point. This makes it possible to estimate the properties of an unknown member of the series from those of its neighbors.
• 4.3: Chemical Reactions of Alkanes. Combustion of Alkanes
As a class, alkanes generally are unreactive because their chemical "affinity" for most common reagents may be regarded as "saturated" or satisfied. Thus none of the C−H or C−C bonds in a typical saturated hydrocarbon, for example ethane, are attacked at ordinary temperatures by a strong acid, such as sulfuric acid, or by an oxidizing agent, such as bromine (in the dark), oxygen, or potassium permanganate. Under ordinary conditions, ethane is similarly stable to reducing agents.
• 4.4: Combustion. Heats of Reaction. Bond Energies
All hydrocarbons are attacked by oxygen at elevated temperatures and, if oxygen is in excess, complete combustion occurs to carbon dioxide and water. The heat evolved in this process - the heat of the combustion reaction, is a measure of the amount of energy stored in the C-C and C-H bonds of the hydrocarbon COMPARED to the energy stored in the products, carbon dioxide and water.
• 4.5: Halogenation of Alkanes. Energies and Rates of Reactions
The economies of the highly industrialized nations of the world are based in large part on energy and chemicals produced from petroleum. Although the most important and versatile intermediates for conversion of petroleum to chemicals are compounds with double or triple bonds, it also is possible to prepare many valuable substances by substitution reactions of alkanes. In such substitutions, a hydrogen is removed from a carbon chain and another atom or group of atoms becomes attached in its place
• 4.6: Practical Halogenations and Problems of Selectivity
Given the knowledge that a particular reaction will proceed at a suitable rate, a host of practical considerations are necessary for satisfactory operation. These considerations include interference by possible side reactions that give products other than those desired, the ease of separation of the desired product from the reaction mixture, and costs of materials, apparatus, and labor. We shall consider these problems in connection with the important synthetic reactions discussed in this book.
• 4.7: Nitration of Alkanes
Another reaction of commercial importance is the nitration of alkanes to give nitroparaffins. Such reactions usually are carried out in the vapor phase at elevated temperatures using nitric acid or nitrogen tetroxide as the nitrating agent.
• 4.E: Alkanes (Exercises)
These are the homework exercises to accompany Chapter 4 of the Textmap for Basic Principles of Organic Chemistry (Roberts and Caserio).

Thumbnail: Structure of propane.