Other Reactions of Organic Compounds

Classifying the chemical reactions of organic compounds makes predicting products of reactions much easier. 

Real-World Reading Link As you eat lunch, the oxidation of organic compounds is probably not on your mind. However, that is exactly what is about to occur as your cells break down the food that you eat to obtain energy for your body. 

You have already read about substitution and condensation reactions in Sections 22.1 and 22.3. Two other important types of organic reactions are elimination and addition. 

Elimination reactions One way to change an alkane into a chemically reactive substance is to form a second covalent bond between two carbon atoms, producing an alkene. The formation of alkenes from alkanes is an elimination reaction, a reaction in which a combination of atoms is removed from two adjacent carbon atoms, forming an additional bond between the carbon atoms. The atoms that are eliminated usually form stable molecules, such as H2O, HCl, or H2. 

O Reading Check Define elimination reaction in your own words. 

Another type of organic reaction is like an elimination reaction in reverse. An addition reaction results when other atoms bond to each of two atoms bonded by double or triple covalent bonds. A hydration reaction is an addition reaction in which a hydrogen atom and a hydroxyl group from a water molecule add to a double or triple bond. An addition reaction that involves the addition of hydrogen to atoms in a double or triple bond is called a hydrogenation reaction. 

Oxidation-reduction reactions also can occur among organic molecules. Oxidation is often recognizable through a gain of oxygen or a loss of hydrogen. 

Classify each of the following reactions as an elimination reaction or an addition reaction. Then state whether each represents hydrogenation, dehydrogenation, hydration, dehydration, or none of those. 

Alkyl halides can undergo elimination reactions to produce an alkene and a hydrogen halide, as shown here. 

Likewise, alcohols also can undergo elimination reactions by losing a hydrogen atom and a hydroxyl group to form water. An elimination reaction in which the atoms removed form water is called a dehydration reaction. In the following dehydration reaction, the alcohol is broken down into an alkene  

The process of catalytic cracking breaks long-chain alkanes into smaller alkanes and alkenes that are more valuable to industry. 

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The reaction of H2 with Bt2 and the reaction of CI2 with hydrocarbons (as well as many other reactions of organic compounds) follow chain mechanisms. Likewise, the reaction between O2 and H2 follows a chain mechanism. Chain mechanisms are important in numerous gas phase reactions, and they will be discussed in more detail in Chapter 4. 

We first encountered nucleophilic substitution in Chapter 4, in the reaction of alcohols with hydrogen halides to fonn alkyl halides. Now we ll see how alkyl halides can themselves be converted to other classes of organic compounds by nucleophilic substitution. 

We have already used the HSAB principle as it applies to linkage isomers in metal complexes. This application to bonding site preference can also be used to show the behavior of other systems. For example, the reactions of organic compounds also obey the principles when reacting with nucleophiles such as SCN- or N02 ... 

Oxidative chain reactions of organic compounds are current targets of theoretical and experimental study. The kinetic theory of collisions has influenced research on liquid-phase oxidation. This has led to determining rate constants for chain initiation, branching, extension, and rupture and to establishing the influence of solvent, vessel wall, and other factors in the mechanism of individual reactions. Research on liquid-phase oxidation has led to studies on free radical mechanisms and the role of peroxides in their formation. 

Ketones feature prominently in accounts of the earliest systematic studies of both synthetic and mechanistic organic photochemistry. They absorb in the more readily accessible wavelength ranges of the ultraviolet, so that some aromatic ketones react even in sunlight, and many of their photochemical reactions lead efficiently to products that can be easily isolated or analysed. Ketones continue to be used as substrates for many studies in photochemistry, and in general they have been more intensively studied than any other group of organic compounds. 

The same type of procedure can be used to estimate AH0 values for many other kinds of reactions of organic compounds in the vapor phase at 25°. Moreover, if appropriate heats of vaporization are available, it is straightforward to compute AH° for vapor-phase reactions of substances which are normally liquids or solids at 25°. The special problems that arise when solutions and ionic substances are involved are considered in Chapters 8 and 11. 

The melting points (more accurately termed the decomposition points) of sugars and some of their derivatives, e.g. osazones, are not so definite as those of other classes of organic compounds they vary with the rate of heating and the differences between individual members are not always large. There are, however, a number of reactions and derivatives which will assist in the characterisation of the simple sugars. 

In this chapter we want to better understand how monomers react together to form long polymer chains. We have already seen a few reactions of organic compounds. For example, in Chapter 4 we wrote an equation for the esterification reaction of an alcohol with a carboxylic add to produce an ester plus water (Equation 5). We pointed out that monomers are usually difunctional organic compounds, where reaction with other suitable difunctional compounds can lead to polymer formation. In Chapter 4 we illustrated this with a polyesterification reaction (Equation 6). We will see that there are several different types of monomers. After reading this chapter you should be able to identify those organic compounds that are monomers and understand how they can react to form polymers. 

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