Brian G. Cox
- Published in print:
- 2013
- Published Online:
- May 2013
- ISBN:
- 9780199670512
- eISBN:
- 9780199670512
- Item type:
- book
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199670512.001.0001
- Subject:
- Physics, Condensed Matter Physics / Materials
Acids and bases are ubiquitous in chemistry. Our understanding of them, however, is dominated by their behaviour in water. Transfer to non-aqueous solvents leads to profound changes in acid-base ...
More
Acids and bases are ubiquitous in chemistry. Our understanding of them, however, is dominated by their behaviour in water. Transfer to non-aqueous solvents leads to profound changes in acid-base strengths and to the rates and equilibria of many processes: for example, synthetic reactions involving acids, bases, and nucleophiles; isolation of pharmaceutical actives through salt formation; formation of zwitter-ions in amino acids; and chromatographic separation of substrates. This book seeks to enhance our understanding of acids and bases by reviewing and analysing their behaviour in non-aqueous solvents. The behaviour is related where possible to that in water, but correlations and contrasts between solvents are also presented. Fundamental background material is provided in the initial chapters: quantitative aspects of acid–base equilibria, including definitions and relationships between solution pH and species distribution; the influence of molecular structure on acid strengths; and acidity in aqueous solution. Solvent properties are reviewed, along with the magnitude of the interaction energies of solvent molecules with (especially) ions; the ability of solvents to participate in hydrogen bonding and to accept or donate electron pairs is seen to be crucial. Experimental methods for determining dissociation constants are described in detail. In the remaining chapters, dissociation constants of a wide range of acids in three distinct classes of solvent are discussed: protic solvents, such as alcohols, which are strong hydrogen-bond donors; basic, polar aprotic solvents, such as dimethylformamide; and low-basicity and low-polarity solvents, such as acetonitrile and tetrahydrofuran. Dissociation constants of individual acids vary over more than twenty orders of magnitude among the solvents, and there is a strong differentiation between the response of neutral and charged acids to solvent change. Ion-pairing and hydrogen-bonding equilibria, such as between phenol and phenoxide ions, play an increasingly important role as the solvent polarity decreases, and their influence on acid–base equilibria and salt formation is described.Less
Acids and bases are ubiquitous in chemistry. Our understanding of them, however, is dominated by their behaviour in water. Transfer to non-aqueous solvents leads to profound changes in acid-base strengths and to the rates and equilibria of many processes: for example, synthetic reactions involving acids, bases, and nucleophiles; isolation of pharmaceutical actives through salt formation; formation of zwitter-ions in amino acids; and chromatographic separation of substrates. This book seeks to enhance our understanding of acids and bases by reviewing and analysing their behaviour in non-aqueous solvents. The behaviour is related where possible to that in water, but correlations and contrasts between solvents are also presented. Fundamental background material is provided in the initial chapters: quantitative aspects of acid–base equilibria, including definitions and relationships between solution pH and species distribution; the influence of molecular structure on acid strengths; and acidity in aqueous solution. Solvent properties are reviewed, along with the magnitude of the interaction energies of solvent molecules with (especially) ions; the ability of solvents to participate in hydrogen bonding and to accept or donate electron pairs is seen to be crucial. Experimental methods for determining dissociation constants are described in detail. In the remaining chapters, dissociation constants of a wide range of acids in three distinct classes of solvent are discussed: protic solvents, such as alcohols, which are strong hydrogen-bond donors; basic, polar aprotic solvents, such as dimethylformamide; and low-basicity and low-polarity solvents, such as acetonitrile and tetrahydrofuran. Dissociation constants of individual acids vary over more than twenty orders of magnitude among the solvents, and there is a strong differentiation between the response of neutral and charged acids to solvent change. Ion-pairing and hydrogen-bonding equilibria, such as between phenol and phenoxide ions, play an increasingly important role as the solvent polarity decreases, and their influence on acid–base equilibria and salt formation is described.
Raymond Brun
- Published in print:
- 2009
- Published Online:
- May 2009
- ISBN:
- 9780199552689
- eISBN:
- 9780191720277
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199552689.003.0014
- Subject:
- Physics, Theoretical, Computational, and Statistical Physics
The first part of this chapter presents experimental data on vibrational relaxation times and vibrational populations obtained in shock tubes and shock tunnels. The corresponding methods of ...
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The first part of this chapter presents experimental data on vibrational relaxation times and vibrational populations obtained in shock tubes and shock tunnels. The corresponding methods of measurement such as interferometry, Raman diffusion spectroscopy, infra-red absorption, and emission are described. The TV and VV relaxation times and non-equilibrium vibrational populations deduced from these measurements are then analysed, and measurements of accommodation and exchange coefficients are described. In the second part, values of dissociation rate constants for various species are proposed. Time-resolved spectra of radiating species (CN, C2) behind strong shock waves are presented; they allow for the analysis of the kinetics of mixtures characteristic of planetary atmospheres. Experimental results of shock stand-off distances over blunt bodies obtained in shock and gun tunnels are compared to computed results. Experimental data on chemical catalycity are discussed. Finally, in the appendices, kinetic models for relaxing and/or reactive mixtures, simulation methods of emission spectra, and precursor radiation measurement in shock tube are discussed.Less
The first part of this chapter presents experimental data on vibrational relaxation times and vibrational populations obtained in shock tubes and shock tunnels. The corresponding methods of measurement such as interferometry, Raman diffusion spectroscopy, infra-red absorption, and emission are described. The TV and VV relaxation times and non-equilibrium vibrational populations deduced from these measurements are then analysed, and measurements of accommodation and exchange coefficients are described. In the second part, values of dissociation rate constants for various species are proposed. Time-resolved spectra of radiating species (CN, C2) behind strong shock waves are presented; they allow for the analysis of the kinetics of mixtures characteristic of planetary atmospheres. Experimental results of shock stand-off distances over blunt bodies obtained in shock and gun tunnels are compared to computed results. Experimental data on chemical catalycity are discussed. Finally, in the appendices, kinetic models for relaxing and/or reactive mixtures, simulation methods of emission spectra, and precursor radiation measurement in shock tube are discussed.
Dennis Sherwood and Paul Dalby
- Published in print:
- 2018
- Published Online:
- August 2018
- ISBN:
- 9780198782957
- eISBN:
- 9780191826177
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780198782957.003.0017
- Subject:
- Physics, Theoretical, Computational, and Statistical Physics
Many reactions in solution involve acids and bases, and so this chapter examines these important reactions in detail. Topics covered include the ionisation of water, pH, pOH, acids and bases, ...
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Many reactions in solution involve acids and bases, and so this chapter examines these important reactions in detail. Topics covered include the ionisation of water, pH, pOH, acids and bases, conjugate acids and conjugate bases, acid and base dissociation constants, the Henderson-Hasselbalch equation, the Henderson-Hasselbalch approximation, buffer solutions and buffer capacity. A unique feature of this chapter is a ‘first principles’ analysis of how a reaction buffered at a particular pH achieves an equilibrium composition different from that of the same reaction taking place in an unbuffered solution. This introduces some concepts which are important in understanding the biochemical standard state, as required for Chapter 23.Less
Many reactions in solution involve acids and bases, and so this chapter examines these important reactions in detail. Topics covered include the ionisation of water, pH, pOH, acids and bases, conjugate acids and conjugate bases, acid and base dissociation constants, the Henderson-Hasselbalch equation, the Henderson-Hasselbalch approximation, buffer solutions and buffer capacity. A unique feature of this chapter is a ‘first principles’ analysis of how a reaction buffered at a particular pH achieves an equilibrium composition different from that of the same reaction taking place in an unbuffered solution. This introduces some concepts which are important in understanding the biochemical standard state, as required for Chapter 23.
Brian G. Cox
- Published in print:
- 2013
- Published Online:
- May 2013
- ISBN:
- 9780199670512
- eISBN:
- 9780199670512
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199670512.003.0002
- Subject:
- Physics, Condensed Matter Physics / Materials
Quantitative treatment of acid–base behaviour is presented, including the definition of acids, bases, and dissociation constants, and the important relationships between solution pH, acid strength, ...
More
Quantitative treatment of acid–base behaviour is presented, including the definition of acids, bases, and dissociation constants, and the important relationships between solution pH, acid strength, acid–base ratios, and species distribution. Molecular structural features of acids, which influence both the acid strengths and their dependence upon solvent, are summarized. They include the bond strength, the ability to stabilize anions and cations by charge dispersion, and the nature of the atom to which the proton is bonded. The acidity of carbon acids, which are widely used in synthetic procedures, is reviewed. Structural rearrangements on ionization of ketones, esters, and nitroalkanes, which allow the negative charge generated on ionization of the C-H bond to reside on oxygen, leads to greatly enhanced acidity. The inductive influence of strongly electron-withdrawing groups ? to the ionizing C-H bond is important for nitriles and sulphones.Less
Quantitative treatment of acid–base behaviour is presented, including the definition of acids, bases, and dissociation constants, and the important relationships between solution pH, acid strength, acid–base ratios, and species distribution. Molecular structural features of acids, which influence both the acid strengths and their dependence upon solvent, are summarized. They include the bond strength, the ability to stabilize anions and cations by charge dispersion, and the nature of the atom to which the proton is bonded. The acidity of carbon acids, which are widely used in synthetic procedures, is reviewed. Structural rearrangements on ionization of ketones, esters, and nitroalkanes, which allow the negative charge generated on ionization of the C-H bond to reside on oxygen, leads to greatly enhanced acidity. The inductive influence of strongly electron-withdrawing groups ? to the ionizing C-H bond is important for nitriles and sulphones.
Brian G. Cox
- Published in print:
- 2013
- Published Online:
- May 2013
- ISBN:
- 9780199670512
- eISBN:
- 9780199670512
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199670512.003.0009
- Subject:
- Physics, Condensed Matter Physics / Materials
Tables of dissociation constants are given for a wide range of substrates in the most extensively studied non-aqueous solvents, including methanol, dimethylsulphoxide, dimethylformamide, ...
More
Tables of dissociation constants are given for a wide range of substrates in the most extensively studied non-aqueous solvents, including methanol, dimethylsulphoxide, dimethylformamide, acetonitrile, and tetrahydrofuran. Equations representing correlations among the solvents and with water are also included.Less
Tables of dissociation constants are given for a wide range of substrates in the most extensively studied non-aqueous solvents, including methanol, dimethylsulphoxide, dimethylformamide, acetonitrile, and tetrahydrofuran. Equations representing correlations among the solvents and with water are also included.
