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Chapter

Cover Chemistry3

Fundamentals  

This chapter describes the structure of an atom in terms of protons, neutrons, and electrons and explains the terms mass number and atomic number and how a simple mass spectrometer can be used to show the isotopic composition of an element. Chemical knowledge is constantly increasing as new compounds are constantly being synthesized and data on the behaviour of chemical systems are being collected and analysed in research laboratories around the world. The chapter highlights the states of matter and phase changes in terms of a kinetic–molecular model of matter. Working out the empirical formula of a compound from its elemental composition and understanding the relationship between empirical formula and molecular formula are also included. The chapter also shows how a simple mass spectrometer can be used to show the isotopic composition of an element.

Chapter

Cover Elements of Physical Chemistry

Proton transfer equilibria  

This chapter describes proton transfer equilibria. It begins by looking at the Brønsted–Lowry theory of acids and bases, according to which an acid is a proton donor and a base is a proton acceptor. The strength of an acid is reported in terms of its acidity constant and that of a base in terms of its basicity constant. The chapter then considers protonation and deprotonation. It differentiates between a weak acid and a strong acid. A strong acid is commonly regarded as being completely deprotonated in aqueous solution. The chapter also differentiates between a strong base and a weak base.

Chapter

Cover Physical Chemistry for the Life Sciences

Proton transfer equilibria  

This chapter is concerned with the transfer of protons between molecules. This is an enormously important cellular process and plays a central role in maintaining the appropriate pH, a measure of hydrogen ion concentration, in the various compartments of cells. The chapter first discusses Brønsted–Lowry theory of acids and bases, which states that an acid is a proton donor, and that a base is a proton acceptor. Next the chapter turns to the protonation and deprotonation of molecules, which are key steps in many biochemical reactions. Hereafter, this chapter turns to polyprotic acids, which is a molecular compound that can donate more than one proton. The chapter concludes with a case study on the fractional composition of a solution of lysine.

Chapter

Cover Organic Chemistry

1H NMR: Proton nuclear magnetic resonance  

This chapter highlights proton (1H) nuclear magnetic resonance (NMR). Proton NMR differs from 13C NMR in a number of ways. 1H is the major isotope of hydrogen, while 13C is only a minor isotope. 1H NMR is quantitative: the area under the peak shows the number of hydrogen nuclei, while 13C NMR may give strong or weak peaks from the same number of 13C nuclei. Moreover, protons interact magnetically (couple) to reveal the connectivity of the structure, while 13C is too rare for coupling between 13C nuclei to be seen. Finally, 1H NMR shifts give a more reliable indication of the local chemistry than that given by 13C spectra. Nevertheless, proton NMR spectra are recorded in the same way as 13C NMR spectra: radio waves are used to study the energy level differences of nuclei in a magnetic field, but this time they are 1H and not 13C nuclei.

Chapter

Cover Foundations of Physics for Chemists

Electrostatics  

This chapter introduces charge as the fundamental property of positive or negative electrons and protons, citing experiments wherein like charges repel while opposite charges attract. It examines the electrostatic interactions that are responsible for the existence of molecules and their chemical and thermodynamic properties. It also discusses the simplest electrostatic reaction between two isolated charged particles that have negligible sizes compared to their separation. The chapter recounts how Charles-Augustin de Coulomb showed experimentally that the magnitude of force between two charged particles is proportional to the product of their charges and to the square of their separation. It clarifies that force is a vector that is collinear with the internuclear separation.

Chapter

Cover Inorganic Chemistry

Acids and bases  

This chapter focuses on the wide variety of species that are classified as acids and bases. It first explains the Brønsted -definition, in which an acid is a proton donor and a base is a proton acceptor. The discussion on the characteristics of Brønsted acids covers the periodic trends in aqua acid strength, simple oxoacids, anhydrous oxides, and polyoxo compound formation. The chapter also introduces the Lewis definition of acids and bases which deals with reactions involving electron-pair sharing between a donor (the base) and an acceptor (the acid). This broadening enables the extension of the discussion on acids and bases to include species that do not contain protons and reactions in nonprotic media. Furthermore, the chapter introduces a molecular orbital description of hydrogen bonding. Lastly, it discusses the nonaqueous solvents and -describes some of the most important applications of acid–base chemistry.

Chapter

Cover Organic Chemistry

Reactions of Alcohols, Ethers, Thiols, Sulfides, and Amines  

This chapter examines the principal methods of preparation of alcohols. It emphasizes that the characteristic properties of alcohols originate in the hydroxy group. Protonation of the O in alcohols and ethers converts poor leaving groups, HO− and RO−, into good ones, H2O and ROH. The chapter then reveals that this enhancement of reactivity by protonation is another example of acid catalysis. The chapter also covers other examples such as acid-catalysed nucleophilic substitution and elimination reactions. In these reactions, R–OH2+ and R–O(H)R+ are comparable with haloalkanes. The chapter also explores the ring-opening reactions of epoxides (oxiranes). It then shifts to discuss the reactions of the sulfur analogues of alcohols (thiols, RSH) and of ethers (sulfides, RSR'), which may be regarded as derivatives of hydrogen sulfide, H2S. It concludes by explaining the reactions of amines.

Chapter

Cover Organic Chemistry

Structural Determination of Organic Compounds  

This chapter looks at how molecular structure is determined. It shows the scope of each method so that, when faced with a structural problem, the most appropriate method for its solution can be identified. The chapter then argues that it is important that organic chemists understand the basis of each principal method they are likely to use for determining the molecular structures of organic compounds, especially ones they have prepared themselves. It also explains the interactions of electromagnetic radiation with molecules, and reviews ultraviolet and visible spectroscopy. The chapter then explains infrared spectroscopy and proton, and carbon nuclear magnetic resonance spectroscopy. It concludes by examining mass spectrometry.

Chapter

Cover Making the Transition to University Chemistry

Instrumental Analysis  

This chapter expounds on the types of instrumental analysis used in chemical laboratories, especially those working with organic compounds. It also notes the fragmentation patterns that characterize a molecule. Mass spectrometry is utilized to search for a compound's molecular formula, while infrared spectroscopy involves the absorption of radiation in the electromagnetic spectrum's infrared region. The energy absorbed makes the bonds vibrate more energetically. Nuclear magnetic resonance (NMR) spectroscopy calculates nuclei's protons and neutrons that possess nuclear spins. The chapter also explains the process of spin-spin splitting or coupling in the NMR spectra as it depends on the number of adjacent protons.

Chapter

Cover Chemistry3

Acids and bases  

This chapter describes two broader definitions of acids and bases and introduces the Brønsted–Lowry theory, in which an acid is defined as a proton donor and a base is defined as a proton acceptor. It also reviews the Lewis theory, in which an acid is defined as an electron pair acceptor and a base is defined as an electron pair donor. This is considered a wide definition as all Brønsted–Lowry acids are Lewis acids, but not all Lewis acids are Brønsted–Lowry acids. The chapter identifies the conjugate acid and conjugate base for an acid–base reaction. It details how to calculate the pH of a solution of a strong or weak acid and a strong or weak base and determine the position of an acid–base equilibrium using Ka and Kb.

Chapter

Cover Chemical Structure and Reactivity

Describing reactions using orbitals  

This chapter looks at how to describe chemical reactions using orbitals. During a reaction, as bonds are formed and broken, the electrons are redistributed. The redistribution of electrons may be followed by calculating how the molecular orbitals change as the reaction proceeds. ‘Curly arrow mechanisms’ summarize the way in which electrons are redistributed during a reaction. Ultimately, the way in which two reactants may react can often be understood by considering the interaction between the highest energy occupied MO (the HOMO) and the lowest energy unoccupied MO (the LUMO). The chapter then looks at the role of protonation in reactions before considering intramolecular orbital interactions and rearrangement reactions.

Chapter

Cover Organic Chemistry

Elimination reactions  

This chapter evaluates elimination reactions. In elimination reactions, a base (nucleophile) removes a hydrogen nucleus (proton), which results in the formation of an alkene with loss of a leaving group. This process can occur by three mechanisms: E2, E1, and E1cB. The mechanism of elimination is dependent on factors including the solvent, the nature of the nucleophile, and the nature of the eliminating species. Elimination reactions often compete with substitution reactions. Bulky nucleophiles, strong bases, and high temperatures favour elimination over substitution, as does increasing the concentration of base. The chapter looks at the major products of elimination reactions, but in practice some of these experiments would yield several impurities, including substitution products.

Chapter

Cover Elements of Physical Chemistry

Polyprotic acids  

This chapter explores polyprotic acids. A polyprotic acid is a molecular compound that can donate more than one proton. It is best considered to be a molecular species that can give rise to a series of Brønsted acids as it donates a succession of protons. The chapter begins by looking at the process of successive deprotonation. Enzymes are polyprotic acids, for they possess many protons that can be donated to a substrate molecule or to the surrounding aqueous medium of the cell. For them, successive acidity constants vary much less because the molecules are so large that the loss of a proton from one part of the molecule has little effect on the ease with which another some distance away may be lost. The chapter then considers speciation, which is the specification of the fractional composition of ions in a solution.

Chapter

Cover Making the Transition to University Chemistry

Atomic Structure  

This chapter looks at the atomic structure and shows that atoms are bonded together to form compounds. The chapter atoms, nucleus, electron, proton, and neutron by referring to the nuclear model. A mass spectrometer can be used to measure the masses of atoms. Electronic structures are often called electronic configurations. The Schrödinger equation can be used to explain arising subshells in the configuration and the electron density. The electron density is defined as the probability of finding a particular electron. The chapter also shows how the current numbering system of the periodic table is based on the Schrödinger equation. The chapter then tackles the ionization energy. This refers to the minimum energy required to remove an electron from an isolated gas atom.

Chapter

Cover Organic Chemistry

Acidity, basicity, and pK a  

This chapter assesses acidity, basicity, and pK a. An acid is a species having a tendency to lose a proton, while a base is a species having a tendency to accept a proton. The measure of acidity or basicity is called pK a; the value of pK a tells us how acidic (or not) a given hydrogen atom in a compound is. Knowing about pK a is useful because many reactions proceed through protonation or deprotonation of one of the reactants, and it is obviously useful to know what strength acid or base is needed. The chapter then considers nitrogen compounds as acids and bases, and looks at carbon acids, the development of the drug cimetidine, and Lewis acids and bases.

Chapter

Cover Introduction to Organic Spectroscopy

Nuclear magnetic resonance spectroscopy: further topics  

This chapter analyses the power of modern pulse-Fourier to transform nuclear magnetic resonance (NMR). The chapter then shows a variety of techniques that assist in the interpretation of spectra and allows for the routine observation of nuclei other than protons. It reviews the original motivation for establishing pulse-Fourier transform methodologies which may be accumulated with a concomitant increase in signal-to-noise ratio for a given period of data collection. It also looks at the possibility of using more than one pulse prior to data acquisition. This controls the behaviour of nuclear spins. The chapter considers how an ensemble of nuclei behave and the processes that occur following pulse excitation of a sample. It uses a pictorial approach to show the vector model of NMR.

Chapter

Cover Foundations of Organic Chemistry: Worked Examples

Acids and bases  

This chapter discusses equilibria and factors effecting acidity and basicity of organic compounds and other areas of chemistry, such as electronegativity of the atom that bear the charge. It examines delocalization, resonance, inductive effects, indicators, and interactions between molecules and ions. It also deals with the protonation on the carbonyl oxygen atom that gives the more stable, delocalized protonated form of the COOH group. The chapter mentions the inductive electron-withdrawing effect of the C=O that helps to weaken the adjacent O-H bond and carboxylic acids that are more acidic than alcohols, whose anions are not stabilized by delocalisation. It refers to Tenormin, which is a drug used in the treatment of high blood pressure, angina, and abnormal heart rhythms.

Chapter

Cover Foundations of Organic Chemistry

Acids and bases  

This chapter examines acids and bases. The Brønsted–Lowry theory states that acids are proton donors, and bases are proton acceptors. Acid/base reactions are largely equilibria and are therefore under thermodynamic control. Many organic acids, such as ethanoic acid, are weak acids. The equilibrium constants are small, much less than 1, and remarkably little of the acid donates its proton to water in aqueous solution. Moreover, many organic acids and bases are largely insoluble in water. The chapter then considers the reactivity of bases as leaving groups and nucleophiles, before comparing acid strengths and base strengths. It also looks at amino acids, which are the building blocks of proteins; they are compounds which have major structural and catalytic roles in all living organisms.

Chapter

Cover Modern Liquid Phase Kinetics

Fast reactions in solution  

This chapter looks at classical kinetic studies of the rates and mechanisms of chemical reactions that normally permit the determination of the overall rate. This rate is constant for reaction and includes several equilibrium constants. The chapter cites the catalysis of reactions by acids and bases which frequently involve the coupling of extremely fast proton-transfer reactions with other processes. It also defines fast reactions as those with half-lives of less than one second, such as reactions that are too fast to be studied conveniently by conventional techniques. The chapter provides a summary of current important techniques for studying fast reactions, including the upper limit for chemical transformations which is set by the period of a molecular vibration. It discusses the steps of bimolecular reactions and covers the approach of the species, control by diffusion, and real chemical transformation.

Chapter

Cover Organic Chemistry

Nucleophilic addition to the carbonyl group  

This chapter details the simplest of all organic reactions: the addition of a nucleophile to a carbonyl group. Nucleophilic additions to carbonyl groups generally consist of two mechanistic steps: nucleophilic attack on the carbonyl group and protonation of the anion that results. Why does cyanide, in common with many other nucleophiles, attack the carbonyl group? And why does it attack the carbon atom of the carbonyl group? To answer these questions, the chapter looks in detail at the structure of carbonyl compounds in general and the orbitals of the C=O group in particular. The chapter then considers the attack of cyanide on aldehydes and ketones; the acid and base catalysis of hemiacetal and hydrate formation; and bisulfite addition compounds.