bluuebunny/crossref_metadata_2025 huggingface dataset:
Solvent effects on reaction rates
Authors: B.G. Cox
Published: September 2023

This chapter reviews the role of solvents in a chemical reaction, and covers the provision of a reaction medium, solvation of the reaction component, and direct involvement as a reactant. It explains how the presence of the solvent alters both the frequency and pattern of collisions between the solute molecules, which can be compared with the gas phase. It also points out that the kinetic energy of the molecules is approximately the same in solution as in the gas phase. The chapter analyses the free space between the solvent molecules that amount to approximately one quarter of the total volume, if close-packed spheres are assumed. It refers to the grouping of the collisions that tends to be repeated with multiple collisions that occur between the same two molecules.
Substitution at sites with coordination number greater than four
Authors: Henderson Richard A.
Published: September 2023

This chapter demonstrates that dissociative mechanisms dominate the substitution reactions at six-coordinate species, although associative mechanisms can still operate in certain circumstances. It analyses the detailed understanding of substitution mechanisms that is great for the six-coordinate Werner-type cobalt (III) complexes and refers to the factors influencing the substitution mechanisms at organometallic-type sites. It also outlines factors that discriminate between associative and dissociative mechanisms in six-coordinate complexes which are the same as those that operate for any coordination number. The chapter elaborates principles in organometallic systems that dominate coordination numbers from four to eight in organometallic systems. It reviews studies on square-planar complexes, wherein the solvent is actively involved in the substitution mechanism.
The insertion reaction
Authors: Henderson Richard A.
Published: September 2023

This chapter focuses on insertion reactions, wherein the overall effect of the reaction bears no relationship to the mechanism and is accomplished by a variety of small molecules. These reactions are most commonly achieved by sulfur dioxide, alkynes, alkenes, carbon monoxide, and nitric oxide, which can be inserted into metal-carbon bonds and metal-hydrogen bonds. The mechanistic description of the reaction is typically that of an intramolecular migration process. The chapter outlines the general principles of the mechanism in relationship to alkenes, carbon monoxide, and nitric oxide.
Mass spectrometry
Authors: Harwood Laurence M. , Claridge Timothy D.W.
Published: September 2023

This chapter talks about a type of analysis which enables the mass of the molecule to be determined, including how it is constructed. It analyses the basic mass spectrometric experiment, first demonstrated by Wilhelm Wien in 1989, wherein individual molecules of a sample are bombarded with high energy electrons, causing the ejection of electrons from the substrate on impact. It also refers to electron impact ionization. This indicates positively charged ions which are accelerated along an electrical potential and pass through a magnetic field. The chapter explains the production of intact radical cation and the impact of an electron which cause sufficient energy to be transferred to the vibrational modes of the molecule. It mentions fragments that retain the positive charge, which are deflected in the magnetic field.
Introduction
Authors: Green N. J. B.
Published: September 2023

This introductory chapter provides an overview of quantum mechanics, which is a subject of central importance in chemistry, and is by nature a mathematical theory. The chemist's approach to the understanding of matter and its chemical transformations is to take a microscopic view, connecting experimental observation with the properties of constituent molecules. However, at the microscopic level, atoms, molecules, and their constituent particles do not obey the familiar laws of mechanics that pertain to the everyday macroscopic world. For example, the existence of molecular line spectra indicates that molecules can be found only at certain well-defined energies, unlike objects at our own scale whose energy appears to be continuously variable. This book aims to explain the fundamentals of quantum mechanics from the point of view of chemistry; describe the areas of chemistry where quantum mechanics is most important; and show how quantum mechanics is applied to chemical problems.
Metal management
Authors: Fenton David E.
Published: September 2023

This chapter examines the management of metals. After the uptake of a metal into an organism from the environment, the metal must be transported to the site where it is to be incorporated for use. Devices for storing excess metals until there is a requirement for use are also necessary. The storage and transport of iron is now quite well understood. However, for other metals, there is a paucity of detailed information. The storage of iron in a non-toxic form is a necessary feature of metabolism as iron is required for the production of functional molecules. The chapter then looks at other storage and transport systems, including metallothioneins and phytochelatins, as well as ceruloplasmin. It also considers the storage and transport of vanadium.
Electron transfer
Authors: Fenton David E.
Published: September 2023

This chapter focuses on biological electron-transfers, which have been divided into two categories. Intramolecular electron-transfer occurs at fixed sites within a single protein, while intermolecular electron-transfer occurs between sites on different proteins. The latter process leads to electron-transfer chains which function as a series of consecutive electron-transfer reactions between pairs of proteins. Typically, electrons are transferred between metal sites arranged within a protein, or complex of proteins. The structure of the protein can play a role in determining the reaction rate constant, and different types of proteins can have rate constants that vary by several orders of magnitude. The chapter then considers blue copper proteins, iron–sulfur proteins, cytochromes, and the photosynthetic pathway.
Nitriles
Authors: Bailey Patrick D. , Morgan Keith M.
Published: September 2023

This chapter explains the properties, synthesis, and reactions of amides. It lists the features of amide bonds: planar, relatively inert, non-basic, weakly nucleophilic on oxygen, and hydrogen bond acceptor and donor. Moreover, the amide bond links amino acids making up all peptides and proteins. The chapter explores the general procedure of making amides through the reaction between an amine and an activated carboxylic acid derivative. Additionally, it looks into hydrolysis, hydrazinolysis, the Vilsmeyer reaction, and the Hoffmann rearrangement as reactions of amides. Amides are relatively unreactive but can undergo attack on the C=O via powerful nucleophiles.
Nitro compounds
Authors: Bailey Patrick D. , Morgan Keith M.
Published: September 2023

This chapter focuses on nitroso compounds. It refers to nitroso compounds as tautomeric with oximes that are thermodynamically more stable. The chapter shares diagrams to reference the bonding. C-nitroso compounds are readily turned to the corresponding oxime if there is a hydrogen-? linked to the nitroso group. Additionally, the chapter discusses the synthesis of aliphatic C-nitroso compounds, aromatic C-nitroso compounds, α-diketones via nitrosis compounds, N-nitroso compounds, and O-nitroso compounds. It mentions how aliphatic C-nitroso compounds tautomerizse to the oxime if an α-hydrogen is present. The α-chloro and acyl Cnitroso compounds are useful in terms of achieving the Diels-Alder reaction.
Radiation and matter
Authors: Brown John M.
Published: September 2023

This chapter begins by defining spectroscopy, which is the study of the way in which electromagnetic radiation interacts with matter as a function of frequency or wavelength. It describes electromagnetic radiation as a transverse waveform that consists of oscillating electric and magnetic fields that point transversely to the propagation of the wave. The chapter emphasizes that the most important point of view of spectroscopy is that energy can be transferred from the source to the detector in the form of electromagnetic radiation. It analyses the exchange between radiation and matter, which involves the interaction between the oscillating electric field in the radiation with the appropriate dipole moment in the molecule. It reviews the practice of spectroscopy that consists of the measurements of the discrete amounts of energy which are passed between molecules and radiation.
Retrosynthetic analysis I: The basic concepts
Authors: Willis Christine L. , Wills Martin
Published: September 2023

This chapter discusses the basic concepts of retrosynthetic analysis. When presented with a specific target molecule, a synthetic route must be designed which enables a pure sample of the desired product to be obtained using a convenient and efficient procedure. Chemists have developed a logical approach for the design of routes for the preparation of organic compounds which involves working the synthesis backwards by making strategic carbon–carbon bond cleavages at points where, in the forward reaction, bond forming reactions may be achieved. This is known as either the disconnection approach or retrosynthetic analysis. The fundamentals of the process of retrosynthetic analysis may be demonstrated by consideration of the synthesis of the secondary alcohol.
Selectivity II: Regioselectivity
Authors: Willis Christine L. , Wills Martin
Published: September 2023

This chapter focuses on regioselectivity. When devising a synthetic route to an organic molecule, substituents and functional groups must be placed in the required positions, i.e. with the correct regiochemistry. The chapter begins by evaluating the regioselectivity of some of the most common methods for the preparation of alkenes. In a regioselective reaction, the formation of one structural (or positional) isomer is favoured. The chapter then describes the control of the reactivity of functional groups which are capable of giving more than one product, with particular reference to: electrophilic addition to a double bond; electrophilic aromatic substitution; electrophilic addition to an enolate; nucleophilic addition to an enone; nucleophilic addition to an epoxide; and oxidation of a ketone to an ester or lactone.
Selectivity III: Stereoselectivity
Authors: Willis Christine L. , Wills Martin
Published: September 2023

This chapter assesses stereoselectivity. The biological and physical properties of organic molecules used as drugs, insecticides, plant growth regulators, perfumes, etc., depend to a large extent on the stereochemistry of substituents and functional groups. Stereochemistry also has an important effect on the reactivity of compounds. In a stereoselective reaction, one stereoisomer of a mixture is produced (or destroyed) more rapidly than another, resulting in the formation of a preponderance of the favoured stereoisomer. Stereoisomers have the same carbon framework and the substituents have identical regiochemistry; however, the isomers differ in their three-dimensional spatial arrangement of atoms within the molecule. Stereoisomers containing two or more stereogenic centres are described as being diastereomers (or disastereoisomers). The chapter also looks at stereospecific reactions.
Selected organic syntheses
Authors: Willis Christine L. , Wills Martin
Published: September 2023

This chapter presents a case history of selected syntheses of a class of natural products known as the pyrrolizidine alkaloids to bring together the aspects of organic synthesis. The pyrrolizidines are a group of alkaloids which are characterized by the presence of the basic necine skeleton. The pyrrolizidine alkaloids exhibit remarkably diverse types of biological activity and have been reported to act as antitumor agents. The chapter then describes four methods for the synthesis of the pyrrolizidine alkaloids. Each route has its own particular merits, e.g. the route to platynecine gives the highest yield, the second method for the synthesis of retronecine uses stereoselectivity to good effect, and of course, the route to (+)–heliotridine is the only enantioselective synthesis.
Computers in instrumentation
Authors: Wayne Richard R
Published: September 2023

This chapter examines some basic concepts of computer techniques which are now widely used in instrumentation. It covers digital integrated circuits that are wired together in an approximate way. These can provide sequences of logical operations of great complexity. It also points out that the computer consists of the hardware, which are logic circuits wired together to provide a small number of sophisticated operations, and the software, which covers the order and repetition of the operations under the control of a program. The chapter recounts the breakthrough in the use of computing techniques that came with the development of microprocessors. It reviews the size and cost of the integrated circuit microprocessors, which make their incorporation into relatively simple instrumentation a feasible proposition.
Inorganic Materials Chemistry
Authors: Weller Mark T.
Published: September 2023

Inorganic Materials Chemistry begins by stating that the chemistry of solid inorganic materials has become a central theme in research and in the teaching of chemistry. This area is, however, often not given enough attention. Topics in this text include transition metal oxides, non-stoichiometry, zeolites, layer compounds chemistry, high temperature superconductors, and fullerides. In addition, the synthesis of these compound types is presented. As well as introducing and describing important solid-state materials, the text addresses the major experimental technique used to study and characterize the powder x-ray diffraction. The basis of this method and associated relevant crystallography is discussed; experimental data from this technique is used to illustrate topics throughout the text. This tying together of an experimental method and the chemistry is a useful approach to adopt.
Application and interpretation of powder X-ray diffraction data
Authors: Weller Mark T.
Published: September 2023

This chapter discusses the application and interpretation of powder X-ray diffraction data. The form of the powder X-ray diffraction data obtained from a material will depend upon the crystal structure it adopts. This structure is delineated by the lattice type, crystal class, unit cell parameters, and the distribution of the various ion and molecule types within the unit cell. As a result of the enormous range of different structures which materials adopt, nearly all crystalline solids have a unique powder X-ray diffraction pattern in terms of the positions of the observed reflections and the peak intensities. In mixtures of compounds, each crystalline phase present will contribute its own unique set of lines to the powder diffraction pattern.
Introduction
Authors: Bochmann Manfred
Published: September 2023

This introductory chapter provides an overview of π-complexes, which are the complexes formed between metals and alkenes, alkynes, alkenyls, and arenes. This form of metal–carbon interaction is unique to transition metals. The moiety containing the π-bond may be neutral, such as ethene or ethyne, or formally anionic, as is the case with cyclopentadienyl or cyclo-octatetraenyl ligands. For transition metals, the 18-electron rule has a predictive function similar to the octet rule for main group elements. It provides a simple ‘rule-of-thumb’ basis for the discussion of structure and bonding, and although there are numerous exceptions, organometallic compounds which fulfil this rule tend to represent relative energy minima. In order to determine whether a compound obeys the 18-electron rule or not, it is useful to follow certain electron counting conventions. Ligands are classified according to the number of electrons they formally donate to the metal centre, following the covalent (electroneutral) counting convention.
Cyclopentadienyl complexes
Authors: Bochmann Manfred
Published: September 2023

This chapter evaluates cyclopentadienyl complexes. In 1948, Miller, Tebboth, and Tremaine, attempting to synthesize amines from olefins and nitrogen in the presence of iron catalysts, found that with cyclopentadiene, an iron-containing compound was formed. The new compound, bis-(cyclopentadienyl)iron, was named ‘ferrocene’ in the realization that it behaves much like a three dimensional arene. Soon afterwards, a whole series of bis-(cyclopentadienyl)metal complexes were prepared; by analogy these have become known as metallocenes. The chapter then looks at the synthesis of metallocenes and bonding in metallocene complexes, as well as the properties of metallocenes and bent sandwich complexes. It also considers cyclopentadienyl as a non-spectator ligand, studying ring slippage and fluxionality. Finally, the chapter explores mono-cyclopentadienyl (half-sandwich) complexes.
Correlation analysis: quantitative relationships between molecular structure and chemical reactivity
Authors: Maskill Howard
Published: September 2023

This chapter evaluates quantitative relationships between molecular structure and chemical reactivity. An appreciation of the relationship between structure and reactivity is central to modern organic chemistry, and qualitative notions are introduced from the earliest stages. Consequently, organic chemists can usually predict whether there has been the replacement of a hydrogen by a methyl, for example, or whether a chlorine by a fluorine in a compound will be rate-increasing or rate-decreasing in a particular reaction. Correlation analysis is a technique which facilitates quantification of such predictions. Correlation analysis involves comparison of the effect of a substituent in a compound in the reaction under scrutiny with the effect of that same substituent upon a standard reaction. The chapter then looks at the uses of σ-values and the Hammett equation. It also considers the Yukawa-Tsuno equation.
Nucleophilic substitution at saturated carbon
Authors: Maskill Howard
Published: September 2023

This chapter examines nucleophilic substitution at saturated carbon. The common feature is that every nucleophile reacts through a lone pair. The bimolecular nucleophilic substitution, SN2, mechanism in solution is believed to be a simple one-step reaction involving the concerted transformation of reactants directly into products, and this mechanism describes the reactions between wide ranges of nucleophiles and alkyl halides. The unimolecular nucleophilic substitution, SN1, is not a single mechanism in the same sense that the SN2 is. Rather, it is a family of mechanisms that share common features. The chapter then looks at the factors affecting mechanism and reactivity in nucleophilic substitution reactions.
Introduction
Authors: Lee Stan , Robinson Graham
Published: September 2023

This chapter provides a general background to fine chemicals manufacture, including the principles and practice of process development. It focuses on the relatively small-scale manufacture of fine organic compounds on a scale of up to tens or occasionally hundreds of kilograms. It also cites examples drawn from experiences within ICI and Zeneca Pharmaceuticals, detailing processes and rationale. The chapter highlights a performance of process development that reflect the culture, philosophy, and availability of equipment and raw materials within ICI and other companies. It reviews the boundary between research and development, which is difficult to define in practice, and notes that the trigger for development to start is when a compound has been identified as having desirable properties.
Homochiral thromboxane antagonists
Authors: Lee Stan , Robinson Graham
Published: September 2023

This chapter looks at pharmaceutical compounds designed to interact beneficially with homochiral living biological systems, i.e., those made up from homochiral amino acids and sugars. It reviews enantiomers and the three different types of biological effects that they are likely to have, such as the separation of the racemate into a single enantiomer that leads to a more potent pharmaceutical agent. The chapter also covers enantiomers which differ in potency, wherein most of the activity resides in one enantiomer and the opposite enantiomer exhibits weaker activity. The chapter outlines the method of separation at the end of synthesis, which is often performed in the research laboratory to obtain small samples of enantiomers and enable the relative biological activity to be assessed. The chapter finally discusses the separation into enantiomers that is achieved at the start or early synthesi.
Open chain and ring structure of monosaccharides
Authors: Davis Benjamin G. , Fairbanks Antony J.
Published: September 2023

This chapter analyzes the empirical formula CH2O, which is the formula of a carbohydrate. This molecule has an oxygen atom attached to each carbon. The chapter states that aldose is the most common type of structure which consists of a linear carbon chain with an aldehyde CHO group at C-1. A varying number of carbon atoms are secondary alcohols CHOH, and there is a primary alcohol at the other end of the chain. The chapter also mentions glyceraldehyde as an example of aldose consisting of several carbons. The chapter explains the Fischer convention which is commonly used for structures that have several stereogenic centres. It highlights the carbon atoms of aldoses that are numbered so that the aldehyde terminus is labelled as C-1.
Enzymatic disaccharide formation
Authors: Davis Benjamin G. , Fairbanks Antony J.
Published: September 2023

This chapter examines the way in which nature constructs and dismantles oligosaccharides. This allows for synthesis and recognizes the factors that need to be considered in disaccharide formation. It describes the classes of carbohydrate-processing enzymes and explains how enzymes are able to be selective in the reactions that they catalyze. The chapter also describes the mechanism of action of glycosyltransferases, including the types of leaving groups that they employ. The chapter refers to the mechanisms of action of glycosidases for inverting and retaining classes and cites examples of syntheses that may be catalyzed by glycosyltransferases and glycosidases. It highlights the two strategies that allow the use of glycosidases as catalysts for synthesizing glycosidic bonds when naturally they cleave them.
Introduction to basic concepts
Authors: Scott Stephen K.
Published: September 2023

This chapter discusses the quantitative interpretation of experimental results in chemical kinetics, which is frequently based on the construction and subsequent analysis of mechanisms or models. It looks at mechanisms that aim for a semiquantitative match to a particular reaction. It also describes models that attempt to catch the main qualitative features of class reactions. The chapter reviews the corresponding reaction rate equations when a sequence of individual reactions that is significant in carrying the reaction from the original reactant to the final products is proposed. It analyses the rate of an elementary step that is given in terms of concentrations of the participating reactants.
Clocks and fronts
Authors: Scott Stephen K.
Published: September 2023

This chapter provides a background on the clock reaction discovered by Hans Heinrich Landolt in 1886, which involves the autocatalytic iodate-bisulphite system. It examines the related phenomena of clock reactions and clock waves in a wide range of systems from gas to solid phases, and into biology. It also mentions the iodate-reductant system which can be simulated using empirical rate-law forms. The chapter describes clock-type behaviour in solution phase reactions, such as gas-phase reactions. These involve the oxidation of simple hydrocarbon. The chapter explains that long induction periods arise in clock reactions associated with thermal runaway. It cites sudden ignition of haystacks as a well-known example of a thermal explosion. It includes a form of clock reaction behaviour observed in the polymerization of a mutant form of haemoglobin.
Orbitals to oxidation state
Authors: Mingos D.M.P.
Published: September 2023

This chapter examines atomic orbitals. An atomic orbital is the wavefunction of an electron in an atom; its square gives the probability of finding the electron at that point. The Schrödinger solution defines the wave equation for the electron in the hydrogen atom as a product of a radial and angular part. The chapter then looks at organometallic compounds before considering the oxidation state, which is a formal device for partitioning electrons in a molecule in a chemically intelligent way. The oxidation state of an atom in a compound is the charge which would result if the electrons in each bond to that atom were assigned to the more electronegative atom.
Sandwich compounds to steric effects
Authors: Mingos D.M.P.
Published: September 2023

This chapter begins by assessing sandwich compounds, which have two planar cyclic ligands bonded through their faces to a metal atom. For transition metal sandwich compounds, the effective atomic number rule is commonly obeyed. The chapter then looks at stability. In everyday language, a stable compound is one which may be stored unchanged in a container over a long period of time. In chemical terms, a much more careful definition has to be adopted and it has to be specified whether the compound maintains its integrity for thermodynamic or kinetic reasons. The temperature dependence of the rates of reaction and the free energies of reactions also require that the conditions of stability must be defined precisely. Finally, the chapter explains steric effects, which can play an important role in many areas of inorganic chemistry.
Alkanes
Authors: G. Denis Meakins
Published: September 2023

This chapter begins with organic nomenclature, or the naming of compounds that is based on the alkanes' names, which are constructed by a rigid procedure. It explains that alkanes do not react with electrophiles, nucleophiles, acids, or bases unless under very rigorous conditions or if very reactive agents are used. It also discusses the important process of hydrogenation that is usually carried out using heterogeneous catalysis, such as a reaction on an insoluble metal surface. The chapter highlights the enthalpy change of halogenation, which may be calculated from bond energies. It illustrates the influence of radical stability in determining the proportions of products, such as the relative stabilities of C radicals.
Alkynes
Authors: G. Denis Meakins
Published: September 2023

This chapter focuses on the differences between alkynes and alkenes, particularly those that affect synthetic work. It explains that one difference concerns the CC double bond, which is usually created from saturated intermediates by elimination but is formed in a different way in alkynes. In these, ethene is widely used in building up the higher members and other compounds containing the triple bond. The chapter observes that alkynes are less reactive than alkenes, but with nucleophiles, the relative reactivity is reversed as simple alkenes do not undergo nucleophilic addition while simple alkynes undergo few additions. It discusses the hydrogenation of an alkyne with a poisoned catalyst that stops at the alkene stage.
Photochemical principles
Authors: Wayne Carol E. , Wayne Richard P.
Published: September 2023

This chapter provides an overview of photochemistry. Life on Earth depends, both directly and indirectly, on the influence that light has on chemistry. Interactions of light with matter make up the subject of photochemistry. If there is one essential feature of photochemistry, it is probably the way in which excited states of atoms or molecules play a part in the processes occurring. The excited states of most concern to the photochemist are those in which the electrons have become distributed into a higher energy arrangement; the species are thus said to be electronically excited. The chapter then looks at the nature of light; wave mechanics and quantum numbers; the selection rules for optical absorption; the laws of photochemistry; and intramolecular energy transfer.
Introduction
Authors: Kirby A.J
Published: September 2023

This introductory chapter provides an overview of stereoelectronic effects. A molecule's bonding electrons serve not only as its skeleton, but also as a rudimentary nervous system. They relay the effects of local perturbations to other centres, more or less efficiently, depending on distance and geometry. Thus, in principle, every nucleus in a molecule can sense the presence of a strongly electronegative atom or group, or the approach of another molecule, or the changes in electron density that happen when bonds are made or broken. In practice, significant effects are quite localized, and it is these that give rise to stereoelectronic effects. They can have profound effects on molecular conformation and the reaction mechanism, and are fundamental to a proper understanding of structure and reactivity. The typical stereoelectronic effect involves an electronic interaction which stabilizes a particular conformation or transition state.
Rearrangements and fragmentations
Authors: Kirby A.J
Published: September 2023

This chapter addresses two groups of reactions of synthetic importance and mechanistic interest, where the key interactions are through two or three bonds: fragmentations and rearrangements. Fragmentation reactions are observed when a strong electron donor interacts with a good leaving group three carbons away. The simplest case is the acid-catalysed fragmentation of a 1,3-diol to an alkene and a ketone or aldehyde. The addition of a nucleophile to a carbonyl group is a simple way to generate a donor oxyanion, and where the addition is sufficiently selective, clean reactions are observed. Meanwhile, rearrangement reactions may be observed even in some conformationally mobile systems, where it must compete with epoxide formation. Although various sorts of rearrangements are known, the most common and important are 1,2-shifts.
Answers to problems
Authors: Kirby A.J
Published: September 2023

3.2 3.15a” would suffer serious steric hindrance.

3.3 Only A.3 has the preferred gauche-gauche conformation (3.16).

3.4 3.33 has both disfavoured...
Symmetry elements, symmetry operations and point groups
Authors: J.S Ogden
Published: September 2023

This chapter describes symmetrical shapes in terms of a plane or line of symmetry and axis of symmetry, which are considered the most identifiable ones exhibited by the majority of symmetrical molecular species. It clarifies that a shape possesses a plane of symmetry if the operation of reflection in the plane results in an equivalent mirror image. It also examines how a shape possesses an axis of symmetry when simple rotation about such an axis leads to an equivalent configuration. The chapter specifies the location of a plane within a molecule and covers various subscripts that identify the position of the plane either in relation to other symmetry elements or to an established coordinate system. It discusses the rotation-reflection axis, which represent the rotational equivalence exhibited by some shapes.
More on representations—the reduction formula
Authors: J.S Ogden
Published: September 2023

This chapter describes character tables and the use of the reduction formula to establish the symmetries of irreducible representations, including other basis functions such as interatomic bonds and atomic orbitals. It defines irreducible representations as the simplest representations obeying the group multiplication tables. These turned out to be rows of 1x1 matrices. It also points out how some representations formed by matrices become reducible instead of irreducible as each can be broken down into two simple representations. The chapter cites examples that show an important representation that relates both to atomic motion and to the symmetry of atomic orbitals. It refers to the method of reduction by inspection, which is one of the quickest ways of obtaining the irreducible representations.
Many-electron atoms and the periodic table
Authors: Cox P. A.
Published: September 2023

This chapter explores many-electron atoms and the periodic table. Schrödinger's equation cannot be solved exactly for atoms with more than one electron. In many ways this is an advantage, as if there did exist exact solutions, they would be too complicated to form useful aids to chemical thinking. A reasonable approximation is to use solutions for each electron resembling those from the hydrogen atom. This orbital approximation forms the basis for our understanding of complex atoms and the periodic table of elements. It is also used in nearly all theories of chemical bonding. The chapter then looks at electron repulsion; electron spin and the Pauli exclusion principle; the 'building-up' principle and the periodic table; and periodic trends.
Dewar-Chatt–Duncanson bonding model
Authors: Mingos D.M.P.
Published: September 2023

This chapter evaluates the Dewar–Chatt–Duncanson bonding model. In classical Werner coordination complexes, the metal-ligand bond is described in terms of donation from a lone pair on the ligand to an empty orbital on the metal. Alkenes and alkynes have no lone pairs and form only very weak complexes with traditional Lewis Acids, but they form stable complexes with transition metals in low oxidation states. The Dewar–Chatt–Duncanson bonding model rationalizes these observations by proposing that the bonding in metal–alkene complexes depends on synergic interactions similar to those found in metal carbonyl complexes. Specifically, the forward donation component involves donation from the filled π-orbital of the alkene to an empty orbital on the metal, and this is supplemented by back donation from filled orbitals on the metal to empty orbitals π* on the alkene.
The p-block
Authors: Wilkins Patricia C. , Wilkins Ralph G.
Published: September 2023

This chapter focuses on the p-block of elements, wherein the filling of three p-orbitals is being completed using six electrons in each series. It explains how elements become more electronegative as the p-orbitals fill as there is a driving force to accept electrons to reach a stable configuration of the noble gases. It also mentions the d-block elements that are essential components of many of the metalloenzymes that catalyse bond cleavage and overcome intrinsic low reactivity. The chapter discusses electrons that are supplied by the FE(II) form of ferredoxin and the ammonia produced for the synthesis of organic compounds required for cell growth. It describes enzyme that contains both an Fe protein and MoFe protein.
Reduction
Authors: Procter Garry
Published: September 2023

This chapter assesses reduction. The two most commonly encountered types of reductions in stereoselective organic synthesis are the reduction of alkenes and the reduction of carbonyl groups. Usually, these are very different types of reaction (although occasionally the same reagent will do both), and each encompasses a very large area of chemistry. The chapter considers some of the more important aspects of these reactions from the point of view of stereoselective synthesis, along with a few examples of their application in organic synthesis. It then looks at the reduction of C–C double bonds and carbonyl groups. The most widely used method of alkene reduction is catalytic hydrogenation, and the reaction is applicable to a very wide range of types of alkenes.
Oxidation
Authors: Procter Garry
Published: September 2023

This chapter addresses oxidation. The oxidation of alkenes can be a powerful method for stereoselective synthesis, and the reactions that the chapter considers are oxidations of alkenes to give epoxides, 1,2-diols, or 1,2-amino alcohols. Epoxides are usually obtained by oxidation of an alkene and are particularly useful as intermediates for organic synthesis, as they can undergo highly selective ring openings with nucleophilic reagents. The epoxidation process usually involves retention of configuration of the alkene, and the ring opening reaction is usually an SN2 process. Meanwhile, dihydroxylation of an alkene using osmium tetroxide is a stereospecific reaction which produces a syn-diol. Aminohydroxylation results in the conversion of an alkene into a 1,2-aminoalcohol derivative, and can be achieved with highly enantioselectivity using the same catalytic system as that used for Sharpless Asymmetric Dihydroxylation.
Hydrolysis and esterification
Authors: Procter Garry
Published: September 2023

This chapter focuses on hydrolysis and esterification. Enzymes can be regarded simply as enantioselective catalysts. However, they are much larger and much more complicated than ‘normal’ enantioselective catalysts. In addition, many enzymes are selective about the structure of the substrates which they will accept, but some of them will accept a reasonably wide range of substrates. There are two basic processes which can be carried out by enzyme hydrolysis: resolution of a racemate by kinetic resolution and conversion of a meso-compound into a chiral product. Typically, the meso-compound used as starting material possesses two enantiotopic ester groups, so hydrolysis of one of these will produce enantiomeric products. This is sometimes referred to as ‘asymmetrization’. Careful chemical manipulation of a single enantiomer produced by asymmetrization can give products in either enantiomeric form.
Answers to problems
Authors: Procter Garry
Published: September 2023

1.1 The product would be expected to have an e.e >0% (see Chapter 10).

1.2 (i) Stereospecific; (ii) Stereospecific; (iii) Stereoselective.

2.1 B1 Gives meso-2,3-dibromobutane. B2 Gives alcohol (±)-B7.

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Measurement of catalytic properties
Authors: Bowker Michael
Published: September 2023

This chapter assesses the measurement of catalytic properties. The most accurate measure of the productivity of a catalyst is an industrial plant. However, industrial plants are inflexible, work in a very narrow window of temperature, pressure, and flow rate, and the catalyst cannot be readily changed. For these reasons, scaled down versions of reactors are used for catalyst testing, and the smallest of these is usually referred to as a microreactor. There are wide range of industrial reactors for heterogeneous reactions, including fixed bed reactors, multitubular reactors, fluidised bed reactors, batch reactors, and flowing bed reactors. The total surface area and pore volume are also important properties of a catalyst that determine how active it is. These can be measured by X-ray diffraction, electron microscopy and particle size distributions, and EXAFS (extended X-ray absorption fine structure). The chapter then looks at the techniques for measuring surface structure.
Catalysis for environmental protection
Authors: Bowker Michael
Published: September 2023

This chapter describes the use of catalysis for environmental protection. Generally, catalysis can be applied to environmental improvement for three reasons. First, processes can be improved in selectivity by the application of catalysts (less by-products). Second, they can be improved in efficiency by lower temperature operation. Third, catalysts can be applied at the 'back-end' of all processes to remove a significant fraction of the pollutants by further conversion. The chapter then looks at the reduction of emissions from petrol vehicles by removing the pollutants from the exhaust. This is achieved by catalytic conversion. The chapter also considers the idea of a catalytic clean-up system to reduce the static sources of pollutants. Finally, it examines the catalytic toilet.
Acetals and ketals
Authors: Jones John
Published: September 2023

This chapter examines acetals and ketals. Aldehydes and ketones react reversibly 1:1 with alcohols under general acid or general base catalysis, to give hemiacetals and hemiketals, respectively. With excess alcohol and a catalytic amount of a strong acid, further reversible reaction takes place to replace the OH group and give an acetal (from an aldehyde) or ketal (from a ketone). If arrangements are made to remove the water from the continuously equilibrating mixture, by distillation or other means, then the aldehyde or ketone is quantitatively converted to an acetal or ketal, as the case may be. The reaction proceeds more easily with aldehydes than with ketones, and is practically limited to primary alcohols. The chapter then looks at dithioacetals, dithioketals, and orthoesters. It also considers the protecting group principle.
Reactions of nucleophiles with carboxylic acid esters
Authors: Jones John
Published: September 2023

This chapter evaluates the reactions of nucleophiles with carboxylic acid esters. The electrophilic reactivity of the carbonyl carbon in esters is less than it is in aldehydes and ketones because it is attenuated by the second oxygen atom. The overall outcome of the commonest pathway for reaction with anionic nucleophiles is quite different, but the first stage, nucleophilic addition, is the same. This process is an acyl transfer reaction, in which the RCO–group is passed from an alcohol oxygen to a nucleophile, liberating the alcohol. Alternatively, and less commonly, the nucleophile may react with the carbon of the alcohol moiety in an SN1 or SN2 fashion. The chapter then looks at hydrolysis and transesterification. It also considers ammonolysis and related reactions, as well as Grignard reagents.
Natural convection
Authors: Winterton R. H. S.
Published: September 2023

This chapter introduces the notion of natural convection. In natural convection, the fluid velocity arises purely from the heating or cooling of the heat transfer surface itself. Heating creates less dense fluid next to the surface which tends to rise under buoyancy. Furthermore, the low velocities (compared to forced convection) give low heat transfer coefficients. In this light, the chapter examines laminar natural convection on a vertical, isothermal plane. From there, it turns to the turbulent boundary layer, before exploring other simple geometries. Next, the chapter discusses the spacing of fins, a worthwhile addition to the issue of low heat transfer coefficients. To conclude, constant heat flux surfaces are addressed.
Calculation of reactor volume and residence time
Authors: Metcalfe Ian S.
Published: September 2023

This chapter examines how to calculate the reactor volume and residence time of material balances, which can be used to design reactors when one reaction is taking place. It also compares the behaviour of the different reactors. For a given conversion, the volume of a plug flow reactor (PFR) will always be less than that of a continuous stirred tank reactor (CSTR) for a positive-order reaction. The PFR tends to operate at higher reactant concentrations than the CSTR, since, in the CSTR, instantaneous dilution with the product takes place. This means that for positive-order reactions, PFRs will exhibit higher overall rates of reaction and therefore will have lower volumes than CSTRs for a given conversion. The chapter then looks at the recycle reactor, in which fresh feed is mixed with a recycle stream and then fed to the PFR.
Simple bonding schemes
Authors: Winter Mark J.
Published: September 2023

This chapter discusses the Lewis description of bonding as described by the combination of Lewis atoms. The three principal chemical bond types are covalent, ionic, and metallic. A covalent bond is the interaction by which two atoms are held together by a pair of electrons located between the two atoms. Ionic compounds consist of regular arrays of cations and anions and ionic bonding consisting of electrostatic attractions experienced between the electric charges of the cations and anions. Meanwhile, metals may be regarded as a regular lattice array of cations, each of which consists of the metal atom less the valence electrons; the valence electrons are detached from any single metal cation and the spaces between the cations are filled with a ‘sea’ of detached electrons.
Atomic structure
Authors: Winter Mark J.
Published: September 2023

This chapter examines the atomic structure. The concept of atoms dates back over 2000 years, while modern concepts of atomic theory date back 250 years. The simplest model for atomic structure based on Ernest Rutherford's conclusions is the Bohr model, a model put forward by the Danish physicist Niels Bohr in 1913. The Bohr model of atomic structure consists of electrons (negatively charged) revolving around the nucleus (positively charged) at certain (quantized) fixed distances in a set of orbits. Erwin Schrödinger then emphasized the wave nature of electrons using wave mechanics. The wave equation solutions for electrons in atoms require the quantum numbers n (principal quantum number), l (azimuthal or angular momentum quantum number), and ml (magnetic quantum number). A fourth quantum number, ms, describes spin. The chapter then looks at the electronic structure and the periodic table.
Hybrid orbital description of bonding
Authors: Winter Mark J.
Published: September 2023

This chapter assesses the hybrid orbital description of bonding. The hybrid orbital view of bonding is a localized view that involves the construction of two-centre, two-electron bonds. Hybrid orbitals for an atom are linear combinations of its atomic orbitals combined in appropriate proportions so that they point towards the attached atoms or groups for that atom. An appropriate hybridization scheme for any particular atom within a molecule is linked with its geometry. The linear geometry is associated with sp hybridization, the trigonal geometry is associated with sp2 hybridization, and the tetrahedral geometry is associated with sp3 hybridization. The chapter then considers benzene, which is one of the most important molecules in organic chemistry.
Covalent models of metal complexes
Authors: Mark J. Winter
Published: September 2023

This chapter describes a model that involves donation into empty metal hybrid orbitals, wherein the nature of the hybrid orbitals depends upon the geometry of the complex. The chapter cites a covalent valence bond model, which has problems that are at least partly resolved by a more sophisticated covalent model called molecular orbital theory. It also explains ML σ-only bonding in metal complexes ML6 that consists of six bonding levels, six antibonding levels, and three nonbonding levels. The chapter mentions complexes that follow the 18-electron rule and attain kinetic stability when all the metal (n+1)s and (n+1)p orbitals are filled with electrons.
Formulae and nomenclature
Authors: Mark J. Winter
Published: September 2023

This chapter introduces a few important conventions and notes earlier conventions that it argues will persist for many years in the chemical literature and nonspecialist literature, including the media. It reviews conventions regarding chemical formulae and line diagrams. It also points out the importance of understanding key guidelines for writing formulae change and that much literature displays chemical formulae in what might be regarded as a nonstandard fashion. The chapter outlines recommendations of procedures for the naming of inorganic compounds which are made by IUPAC. It examines two naming conventions: additive, which is for coordination complexes, and substitutive, which is for organometallic complexes.
Fourier transform NMR
Authors: Hore P. J. , Jones J. A. , Wimperis S.
Published: September 2023

Introduction

This chapter reviews some of the basic elements of Fourier transform NMR spectroscopy, including a brief introduction to two-dimensional NMR. We shall not refer to specific experiments, but will attempt to lay the foundations for the more detailed discussions that follow. As with the...
Product operators II
Authors: Hore P. J. , Jones J. A. , Wimperis S.
Published: September 2023

Introduction

We now start to use product operators to describe pulse sequences that cannot be satisfactorily understood using the vector model. In this chapter we deal with one-dimensional experiments.