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Chapter

Cover Chemistry for the Biosciences

Reaction mechanisms: the chemical changes that drive the chemistry of life  

This chapter examines four key reaction mechanisms: substitution, addition, elimination, and condensation. During substitution, an atom or group of atoms from one reactant is substituted for an atom or group of atoms on a second reactant molecule. Substitution may be electrophilic or nucleophilic, depending on the nature of the molecule that changes as a result of the reaction. During an addition reaction, two molecules combine in such a way that the product contains all the atoms of both reactants. By contrast, during an elimination reaction, a reactant loses some of its component atoms; these atoms form one or more new compounds. Elimination may proceed via a two-step E1 mechanism, or a one-step E2 mechanism. Finally, during a condensation reaction, two reactants combine to form a single product; a further molecule is eliminated during the reaction, which forms an additional product. The chapter then considers hydrolysis reactions and how biochemical reactions exemplify the reaction mechanisms discussed earlier in the chapter.

Chapter

Cover Polymers

Step-growth polymers  

This chapter evaluates step-growth polymers. In the case of step-growth (condensation) polymers, the mechanism is simply an extension of the normal organic condensation reactions in which a small molecule is expelled as the link is built. This is a different situation to the chain polymerizations described in the previous chapter. It is assumed that most step polymerizations involve bimolecular reactions as key mechanistic processes. The chapter then looks at the kinetics of step polymerization. It also considers the commercial preparations of step-growth polymers. The industrial preparation of polyethylene terephthalate (PET) exploits the reversibility of esterification. A key feature in polymer technology is the manipulation of polymer properties by post-polymerization processing. PET behaviour is affected by its crystallinity.

Chapter

Cover Making the Transition to University Chemistry

Aldehydes and Ketones  

This chapter describes aldehydes and ketones. Aldehydes have one alkyl group and one hydrogen atom attached to the carbonyl carbon. Ketones have two alkyl groups and resist oxidation. Both aldehydes and ketones contain the carbonyl group which has a carbon atom doubly bonded to an oxygen atom. Fehling's solution and Tollens' reagent can also help determine the differences between aldehydes and ketones. Oxidation can also help the reduction of aldehydes and ketones to primary and secondary alcohols respectively. The chapter also explains nucleophilic addition, condensation reactions, and alpha carbon reaction of aldehydes and ketones.

Chapter

Cover Aromatic Heterocyclic Chemistry

Introduction  

This introductory chapter provides an overview of heterocyclic chemistry, which is a large and important branch of organic chemistry. Heterocycles occur in nature, for instance in nucleic acids and indole alkaloids. Synthetic heterocycles have widespread uses as herbicides, fungicides, insecticides, dyes, organic conductors, and, of course, pharmaceutical products such as the anti-ulcer drug. Any ring system containing at least one heteroatom can be described as heterocyclic. This broad definition encompasses both aromatic heterocycles and their non-aromatic counterparts. Aromatic heterocycles are described as being heteroaromatic. The chapter then looks at aromaticity and heteroaromaticity, before considering the synthesis of heterocycles. Many classical syntheses of heterocycles revolve around the condensation reaction in its various guises.

Chapter

Cover Core Carbonyl Chemistry

Aldol condensations and related reactions  

This chapter explores aldol condensations and related reactions. The reactions of enols and enolates with electrophiles are not confined to the simple α substitutions so far discussed. The electrophile can also be a carbonyl compound, and, as with the attack of simpler nucleophiles on carbonyl groups, the formation of a tetrahedral adduct can be followed by protonation, dehydration, or loss of a leaving group. Aldol condensations, whether carried out with acid or base catalysis, are often followed by spontaneous dehydration. Dehydration is practically the norm for acid-catalyzed conditions. The chapter then looks at crossed aldol condensations; enolate acylation reactions; the Thorpe–Ziegler cyclization; and αβ unsaturated carbonyl compounds.