Fundamental Reaction Types

Reactions can be categorized into types. The following lists four reaction types using hypothetical elements or molecules A, B, C, and D. 

Single Displacement A + BC — B + AC (also called single replacement) 

Double Displacement AB + CD- AD + CB (also called double replacement 

Some important reaction types not shown here are redox, combustion, Bronsted-Lowry acid-base, and Lewis acid-base. We will cover these types later in this book. Reaction types are not mutually exclusive, so one reaction can fall into more than one type. 

It you don t understand where the numbers came from in the table, take another look. You should understand this for the MCAT. 

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Although the present chapter includes the usual collection of topics designed to acquaint us with a particular class of compounds its central theme is a fundamental reaction type nucleophilic addition to carbonyl groups The principles of nucleophilic addition to aide hydes and ketones developed here will be seen to have broad applicability m later chap ters when transformations of various derivatives of carboxylic acids are discussed... 

In the preceding chapter you learned that nucleophilic addition to the carbonyl group IS one of the fundamental reaction types of organic chemistry In addition to its own reactivity a carbonyl group can affect the chemical properties of aldehydes and ketones m other ways Aldehydes and ketones having at least one hydrogen on a carbon next to the carbonyl are m equilibrium with their enol isomers... 

The stereochemistry of the most fundamental reaction types such as addition, substitution, and elimination are described by terms which specify the stereochemical relationship between the reactants and products. Addition and elimination reactions are classified as syn or anti, depending on whether the covalent bonds which are made or broken are on the same face or opposite faces of the plane of the double bond. 

Electrophilic aromatic substitution (Section 12.1) Fundamental reaction type exhibited by aromatic compounds. An electrophilic species (E ) attacks an aromatic ring and replaces one of the hydrogens. 

We said in A Preview ofCnrbonyl Compounds that much of the chemistry of carbonyl compounds can be explained by just four fundamental reaction types nucleophilic additions, nucleophilic acyl substitutions, o substitutions, and carbonyl condensations. Having studied the first two of these reactions in the past three chapters, let s now look in more detail at the third major carbonyl-group process—the a-substitution reaction. 

The a-substitution reaction of a carbonyl compound through either an enoi or enolate ion intermediate is one of the four fundamental reaction types in carbonyl-gron p chem istrv. 

The fundamental reaction types suitable for metal-mediated syntheses of allenes (Scheme 2.1) comprise SN2 nucleophilic substitution reactions of propargylic elec-... 

The articles of this volume again clearly demonstrate that photoinduced electron transfer is one of the very few fundamental reaction types (Roth) both for natural and artificial systems. 

The fundamental reaction types involved in the formation of polymeric silica materials (via, for example, cyclic oligomers similar to those shown in Figures 4 and 5) from monomeric (RO)4Si compounds are shown in Scheme 43. 

Problem 20.26 Give equations for the individual steps probably involved in the conversion of calcium cyanamide into ammonia in the presence of water. What other product or products will be formed in this process Label each step with the name of the fundamental reaction type to which it l longs. 

The insecticide called DDT, l,l,l-trichloro-2,2-bis-(/7-chlorophenyl(ethane, (p-ClC6H4)2CHCCl3, is manufactured by the reaction between chlorobenzene and tnchloroacetaldehyde in the presence of sulfuric acid. Outline the series of steps by which this synthesis most probably takes place make sure you show the function of the H2SO4. Label each step according to its fundamental reaction type. 

As we said in Chapter 5, there are three fundamental reaction types polar reactions, radical reactions, and pericyclic reactions. Let s review each to see how the reactions we ve covered fit the different categories. 

Many mechanisms in organic chemistry start with an acid/base reaction. This may be just a simple Bronsted-Lowry protonation of a hydroxyl group, which results in the activation of a C-OH bond or it may be a Lewis acid/base reaction as, for example, when aluminium trichloride complexes with a halogenoalkane in the first step of the Friedel-Crafts reaction. In each case, the initial intermediate usually reacts further and leads to the desired product. In inorganic chemistry, the acid/base reaction may be all that is of interest, e.g. the treatment of a carbonate with an acid to liberate carbon dioxide. However, it is unusual in organic chemistry for the acid/base reaction to be an end in itself. It is for this reason that acid/base characteristics are normally considered as a property of the molecule, similar to the nucleophilic and electrophilic properties to which they are closely related, rather than as a fundamental reaction type as is the case in inorganic chemistry. 

Organic reaction mechanisms can similarly be reduced to a small number of fundamental reaction types, namely substitution, addition, elimination, rearrangement and redox reactions. 

These six fundamental reaction types are the basis of metabolism. Remember that all six types can proceed in either direction, depending on the standard free energy for the specific reaction and the concentrations of the reactants and products inside the cell. An effective way to learn is to look for commonalities in the diverse metabolic pathways that we will be examining. There is a chemical logic that, when exposed, renders the complexity of the chemistry of living systems more manageable and reveals its elegance. 

The hydrolysis of (EtO)4Si (and the subsequent polycondensation of Si-OH containing molecules) has been the subject of considerable investigation because of its importance in the fabrication of glasses and colloidal silica via the sol-gel process see Sol-Gel Synthesis of Solids). Hydrolysis of the Si-0 bond in alkoxysilanes is also very widely used to attach silicon compounds to surfaces and in coupling reactions. The fundamental reaction types involved in the formation of polymeric silica materials (via, for example, cyclic oligomers similar to those shown in Figures 4 and 5) from monomeric (RO)4Si compounds are shown in Scheme 43. 

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