bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phase Integral Approximations
Authors: Child M S 
Published: November 2023

Abstract
The simplest representation for the quantum mechanical wavefunction in terms of classical quantities is due to Jeffreys (1925), Wentzel (1926), Kramers (1926), and Brillouin (1926a,b). It generalizes the free-motion form, ψ = exp(ipx/h), by allowing for variation in the momentum p(x) as a function of position, a correction that replaces the exponent by a phase integral, ∫p(x) dx, and introduces a normalization term related to the local velocity. A similar description may also be applied in classically forbidden regions by allowing the momentum to become imaginary, p(x) = i|p(x)|, provided that the local de Broglie wavelength, λ.(x) = h/p(x), varies sufficiently slowly with x. Details are given in Section 2.1 and discussed at greater length by Froman and Froman (1967) and Froman (1980).
Quantization
Authors: Child M S 
Published: November 2023

Abstract
Questions of quantization turn on a proper treatment of normally isolated regions where the JWKB description, expressed by eqn (2.13), breaks down. The most obvious of such special regions are those around the classical turning points, at each of which the analysis in Sections 2.2 and 2.3 yields an associated so-called Maslov (1972) phase correction of π/4; Delos (1986) and Littlejohn and Robbins (1987) discuss this Maslov correction from a more fundamental standpoint and Appendix A and parts of Section 11.2 bear on its choice. Other special regions around potential singularities are most conveniently handled by introducing a Langer (1932) correction term to the physical potential function (see Section 2.3). It is shown in Section 3.1 that systems with no other complications may be quantized by the Bohr-Sommerfeld rule
(3.1)∮p(q)dq=(n+δ)h,  n=0,1,2,3⋯
where n is the quantum number and b is a Maslov index, which takes the values ½, 0, ½ for vibrational, plane rotational, and orbital motion respectively.
Angle–Action Variables
Authors: Child M S 
Published: November 2023

Abstract
The Bohr–Sommerfeld quantization rule, 12π∮pdq =(n+δ)ℏ,
arose in Section 3.1 from the boundary conditions on the JWKB wave function. Here it is set in the context of classical angle–action theory from which it evolved (Bohr 1913). The idea is that any bound periodic motion can be simply described in special action-angle variables, termed here (1, α), such that the action, defined in Cartesian variables by the equation
Atom–Atom Scattering
Authors: Child M S 
Published: November 2023

Abstract
Atomic collisions are normal1y termed elastic or inelastic. The former lead simply to momentt1m transfer between the collision partners, or equivalently to a change in the direction of their motions; the latter lead also to a simultaneous transfer of energy between internal motion and translation. This chapter lays the foundations of the theory in the elastic context and indicates, in the final section, how it generalizes to the inelastic case. The theory stems from the seminal papers of Ford and Wheeler (1959) which precipitated the recent revival of interest in semiclassical mechanics. The review by Berry and Mount (1972) was also very influential.
Principles
Authors: Procter Garry 
Published: November 2023

Abstract
In order to achieve asymmetric synthesis, at least one component of the reaction must be chiral and non-racemic. If there is no asymmetric component in the reaction, then transition states which lead to enantiomers will themselves be enantiomeric, equal in energy, and a racemate must be formed. In principle, the use of a chiral, non-racemic substrate, reagent, solvent, or catalyst should lead to asymmetric synthesis. In general terms, any feature of the reacting system which would cause the possible transition states for the reaction to be diastereoisomeric (where they would normally be enantiomeric) could lead to the preferential formation of one diastereoisomer or enantiomer. This follows because transition states which are diastereoisomeric need not be of the same energy and consequently one of the possible products could be formed more rapidly. The various possibilities will be considered in this chapter.
Additions to carbonyl compounds
Authors: Procter Garry 
Published: November 2023

Abstract
The addition of a nucleopbile to a carbonyl group is a fundamental reaction of organic chemistry, and a cornerstone of organic synthesis. As such it is impossible to cover all such reactions which are relevant to asymmetric synthesis in one chapter. Enantioselective reduction of ketones is covered in Chapter 7 along with the reduction of other functional groups, and asymmetric aldol reactions of aldehydes is the subject of Chapter 5. Accordingly, this chapter is concerned mainly with the addition of nucleophiles to ketones and aldehydes in which one or more new chiral centres are formed and which result in non-racemic products. The most straightforward and commonly encountered example of this type of process is the addition of non-chiral nucleophiles to chiral aldehydes and ketones, and this will be the subject of the first part of this chapter. This in itself constitutes a large area of organic synthesis, and selected examples will be used to illustrate the important general principles and applications.
Hydrolysis and esterification
Authors: Procter Garry 
Published: November 2023

Abstract
There are two general approaches to the use of hydrolysis and esterification in asymmetric synthesis, and usually both involve the use of enzymes as asymmetric catalysts. In one case the asymmetric catalyst is used in a kinetic resolution process in which one enantiomer of a racemic mixture reacts more rapidly than its antipode. In the example shown (Fig. 9.1) the lipase-catalysed hydrolysis of the (1R,2R)-enantiomer of 9.1 is rapid. In effect, the (1S,.2S) enantiomer is not a substrate for the enzyme, and essentially all of the fastreacting antipode is hydrolysed to the alcohol. As in all simple resolution procedures, the yield of an individual enantiomer cannot be greater than fifty per cent, and the two enantiomerlc components, ester (1S,2S)-9.l and alcohol 9.2 still need to be separated.
General procedures: starting materials and reaction guidelines
Authors: Taylor Richard J K , Casy Guy 
Published: November 2023

Abstract
This chapter contains information concerning the starting materials required for organocopper reactions (commercial availability, preparative procedures, purification, etc.), together with a discussion of the apparatus and techniques commonly employed when carrying out such reactions. A number of copper salts and their complexes have been employed for the preparation of cuprate reagents, copper(I) iodide being the most popular. It has been shown in comparison experiments, however, that CuCN and CuBr-SMe2 are equally useful, if not better, organocuprate precursors. Copper(II) salts used in copper-catalysed Grignard reactions are reduced to the active copper(I) species by excess Grignard reagent. Table 2.1 lists copper-containing starting materials that have been employed in organocopper reactions and includes brief notes on suppliers, preparation/purification procedures, and synthetic utility.
Preparation of organocopper reagents using active copper
Authors: Rieke R D , Klein W R 
Published: November 2023

Abstract
Organocopper reagents have intensively been used in synthetic chemistry. The vast majority of organocopper reagents are prepared by a transmetallation reaction involving an organometallic reagent and a copper(I) salt. A variety of organometallic reagents, derived from metals more electropositive than copper, have been utilized in the preparation of organocopper reagents. The most common organometallic precursors have been organomagnesium and organolithium reagents. This approach severely limits the functionality that may be incorporated into the organocopper reagent. The use of traditional lithium or Grignard precursors can be circumvented by using a highly reactive zero-valent copper which directly undergoes oxidative addition to organic halides.
Preparation of highly functionalized reagents
Authors: Knochel Paul , Rozema Michael J , Tucker Charles E 
Published: November 2023

Abstract
Many organocopper reagents are prepared from the corresponding magnesium or lithium organometallics. Unfortunately, this approach precludes the presence of most functional groups in these copper reagents, since they would not be tolerated in the starting magnesium or lithium reagent. However, functionalized copper reagents of the type FG—RCu(CN)ZnX can be prepared starting from organozincs (RZnX or R2Zn) by performing a trans-metallation using the soluble copper salt CuCN•2LiCl (eqn 1). Since organozincs bearing a wide range of functionalities such as a cyanide (Protocol 1), an ester (Protocol 2), a ketone, an enone (Protocol 4), an amine, a terminal alkyne (Protocol 3), a phosphonate, a halide, sulfur functionalities (SCOR, SR, SOR, SO2R), or a trialkoxysilyl group [Si(OR)3] can be easily prepared, this method offers a general access to polyfunctional copper reagents.
Me3SiCl-accelerated conjugate addition reactions of organocopper reagents
Authors: Nakamura Eiichi 
Published: November 2023

Abstract
Conjugate addition to α,β-unsaturated carbonyl compounds represents an archetypical reaction of organocopper reagents (eqn 1). Various reagents including the classical Grignard-based catalytic copper reagent, the Gilman reagent (R2CuLi), and the ‘RCu•BF3’ reagent have been developed to improve the efficiency of the process by enhancing the reactivities of the reagents and by suppressing side-reactions such as 1,2-addition. Because of the paramount importance of the conjugate addition in organic synthesis, research efforts continue to make the reaction more versatile and more reliable. This chapter describes the Me3SiCl-accelerated reactions of organocopper reagents—a methodology which has proven its great synthetic utility in the past several years.
Synthetic applications of silylcuprates and stannylcuprates
Authors: Fleming Ian 
Published: November 2023

Abstract
Silylcopper and stannylcopper reagents and the corresponding cuprates react with many of the same substrates (Scheme 12.1) as their carbon-based counterparts. The products carry on their carbon framework a silyl or stannyl group, with which many transformations can be carried out, replacing these functional groups with carbon groups or with other functional groups. In addition, silylcuprates and stannylcuprates react with unactivated allenes to give vinyl or allyl derivatives depending upon the structure of the allene. In general, silylcopper and stannylcopper reagents and the corresponding cuprates appear to be thermodynamically more stable in THF solution than their carbon-based counterparts, allowing them to be treated with their substrates at temperatures of 0°C and above over several hours if necessary, although it rarely is, because they appear to be simultaneously kinetically more reactive than the carbon-based reagents, reacting with substrates such as allenes and α,β-unsaturated esters that carbon-based cuprates do not react with in the normal course of events.
Powder diffraction: data collection, refinement, results
Authors: Baerlocher Ch. 
Published: November 2023

Abstract
The principle handicap of the powder method is the fact that the three dimensional diffraction data are projected onto a one-dimensional array. The associated loss of information has given the powder method a bad reputation in many quarters of the natural sciences. Powder data is viewed as something to be avoided. However, this picture has changed in recent years. It is, of course, still true that powder data are, for the most part, inferior to single crystal data, but the progress achieved in both instrumentation and data analysis have led to a growing awareness of the potential of the powder method, and to an increasing recognition of the quality of the results. This success is due, to a significant extent, to the Rietveld method. In this method the problem of overlapping reflections is circumvented by fitting the whole diffraction pattern step by step.
The Solution of Large Small-Molecule Structures and Small Macromolecules
Authors: Sheldrick George M 
Published: November 2023

abstract
As pointed out in a recent editorial inScience (Moffat, 1992), the phase problem is probably most difficult to solve for ‘mid-sized’ molecules of about 200-500 non-hydrogen atoms. Direct methods rarely fail on structures of less than I 00 atoms and are often successful up to about 200 atoms; the largest unknown structure to be solved purely by direct methods is probably gramicidin-A, with 334 unique atoms (Langs, 1988). Classically, most proteins have been solved by the preparation of heavy-atom derivatives, but the introduction of such atoms distorts smaller molecules severely, leading to lack of isomorphism, an essential requirement of the MIR method. Molecular replacement - using a fragment of a related structure as a search probe, usually in Patterson space - is applicable to both small molecules and macromolecules, but many mid-sized structures of biological interest possess more conformational flexibility than this approach can tolerate.
Charge density determination by X-ray diffraction
Authors: Koritsánszky Tibor 
Published: November 2023

Abstract
Many aspects of the chemical bond and molecular structure are directly related to the electron density which can be determined by advanced theoretical and experimental techniques. Each method has its own advantages and limitations and their applicability is subject to different conditions. The molecular electron distribution continuously rearranges itself due to the motion of the nuclei. Under certain assumptions the averaged dynamic distribution is deducible from the static density of the equilibrium structure. The X-ray is scattered by the electrons and the diffracted intensity is related to the electron distribution. The simplest theory applied to interpret the measurement states that the time averaged scattering is dominated by the scattering from the thermally averaged distribution. The observed data are limited and their interpretation must involve modelling.
User interface management systems (UIMS) for crystallography
Authors: Bourne Philip E 
Published: November 2023

Abstract
Advances in hardware and software technology are changing the way crystallographers interact with the computer. Bit-mapped graphics displays as found on workstations, X-terminals, and personal computers, when combined with Graphical User Interface (GUI) software, provide a more sophisticated interface beyond that available using a character-based terminal. To date, most crystallographers use only the standard screen objects supplied with the GUI. These objects include terminal emulation windows for multi-tasking and desktop accessories such as calculators, notepads, and user executives. (User executive is one of several terms for screen objects that simplify interaction with the base operating system.)
New approaches to crystallographic software
Authors: Murray-Rust Peter , Zelinka Jan 
Published: November 2023

Abstract
The problem of developing and maintaining software systems is enormous and has reached a crisis point in many disciplines - crystallography is no exception! Most disciplines have code developed over many years, by many authors with varying degrees of coordination. When people on a project move away, or the code has to be ported to a new machine it is often simplest (though very costly) to rewrite the system from scratch! Crystallographic software development has often been imaginative and effective. Among our community’s contributions have been free-format input, graphical output, high-performance graphical techniques and databases. The collaboration in the community is also a very important factor, leading to program libraries, and integration of many different authors’ work in packages. This philosophy puts crystallography in an excellent position to take advantage of the new software techniques that are becoming available.
Chemical transformations
Authors: Isaacs Neil S 
Published: November 2023

Abstract
Only a brief outline of the effects of pressure on rates and equilibria is given here since the subject is amply documented elsewhere.1-4 It has long been appreciated that the position of a chemical equilibrium may be shifted by the application of external pressure in reactions in both the liquid and the gaseous phase. This shift in equilibrium favours the direction of the reaction which results in the smaller volume; this is an application of the Le Chatelier’s principle. In gas-phase reactions the term volume denotes the total volume of the system; in dilute solutions the term volume denotes the algebraic sum of the partial molar volumes of the individual reagents and products.
Cryptands
Authors: Dietrich Bernard 
Published: November 2023

Abstract
The cryptands were first prepared in 1969 and form a series of well-defined complexes (cryptates) with alkali and alkaline-earth cations. In this chapter the synthesis of the first cryptand, 8, a macrobicyclic ligand, will be described. The schematic representation (Fig. 5.1) shows that one deals with a multi-step synthesis. The major drawback of this approach is the rather large number of synthetic steps, but the route offers the advantage of being able to construct unsymmetrical compounds (A ≠ B ≠ C).
The Natural Selection of the Chemical Elements
Authors: Williams R J P , Da Silva J J R Frausto 
Published: November 2023

Abstract
The central thesis of The Natural Selection of the Chemical Elements is that the inanimate environment and living organisms are intimately connected, and that the evolution of both has been interactive and interdependent: the environment and life developed together. The authors show that this can be explained in terms of the properties of the chemical elements and their compounds, especially as compounds have developed with time. The first part of the book discusses the physical and chemical balance between ordered and disordered systems and then analyses organisation in both the animate and inanimate worlds. Appropriate thermodynamic and kinetic principles are given to support this analysis. The application of these principles to the development of both inorganic (geographical) and organic chemical systems is then described, providing a basis for understanding the evolution of life in terms of the interaction of both types of chemistry within ever more complex organisations. The book concludes by examining the long-term consequences of man's selection and manipulation of chemicals for his own purposes which may have consequences for the long-term future of life from changes in the environment - not only due to bulk but also to trace element alterations.
Limited phases, fields and compartments
Authors: Williams R J P , Da Silva J J R Frausto 
Published: November 2023

Abstract
In this chapter we wish to approach more closely the nature of the observable systems around us be removing in steps the assumptions that were employed in our discussions of equilibria in Chapters 4 and 5. These assumptions were that: (1) the phases had no surfaces, but as soon as we limit the total amount of a system, which we must do now, surfaces become important-the real world around us is constrained by divisions of space with surfaces; (2) there were no fields acting on a phase; however, as soon as we consider contact or a region between phases, that is, phases with surfaces, we must consider fields gravitational, mechanical and electrical; (3) there was equilibrium transfer of material and energy between phases, but in the real world there are boundaries between compartments containing phases that prevent at least some transfer; for example, the presence of semipermeable membranes is the basis of living constructs. Clearly, these three additional features, surfaces fields, and transfer of matter or energy, limit the applicability of the previous discussion of both bulk phases (Chapter 4) and of dilute solutions in isolated phases (Chapter 5). We must, therefore, look first at the effects of limited total amounts of material and the presence of fields on the variance of systems, as predicted by an extended form of the phase rule. We need then to describe the effects of barriers to transfer between compartments, that is, removal of the transfer equilibria for both bulk and dilute components. We shall find that, when we add all these factors together, substances around us cannot but be extremely diversified and far from even local equilibrium. However, as we explained in Chapter 3, it is only by reference to equilibrium that we can gain the basic understanding necessary for the appreciation of out-of-equilibrium systems and the directions of change. One of the major considerations in Chapters 4 and 5 was to establish the limits of variance of systems, that is, the number of degrees of freedom, from the use of equilibrium considerations in the phase rule. We, therefore, start the discussion in this chapter with a brief summary of the position we established in those chapters.
Organoiron chemistry 1: ferrocene and dienyl iron tricarbonyl cation chemistry
Authors: Richards Christopher J 
Published: November 2023

Abstract
This chapter deals with two differing applications of organoiron chemistry to organic synthesis. In the first section the chemistry of ferrocene is examined, in particular the reactions required for the construction of ferrocene-based ligands, which have found wide usage in asymmetric catalysis. In contrast, the cationic dienyl iron tricarbonyl complexes studied in the second section have been employed directly in many elegant total syntheses of complex organic structures.
Acylation and alkoxycarbonylation of the amino group
Authors: Barrett Graham c. 
Published: November 2023

Abstract
The various categories of reaction falling under the heading 𠄘N-acylation or N-alkoxycarbonylation of an a-amino acid𠄙 include several important synthetic processes, as well as covering the most common purposes (a) for N protection during synthesis, and (b) for the provision of samples for amino acid analysis.
Mono- and di-alkylation of the amino group
Authors: Barrett Graham c. 
Published: November 2023

Abstract
The prolonged reaction of an amino acid in solution with an alkyl halide leads to mixtures of secondary and tertiary amines. Continued alkylation ultimately generates the corresponding quaternary ammonium salt of the amino acid ester. This is an inefficient process in terms of organic synthesis, and reliable routes to N-alkylamino acids call for a more painstaking, less direct, approach. Reaction of an amino acid with an aldehyde, followed by reduction of the resulting alkylol or Schiff base, has been found to be reliable, although it is not often used. Weinreb and co-workers showed that simple N-hydroxymethyl amides R1conhch OH undergo acid-catalysed reductive alkylation (hydrogen-palladized charcoal) to give N-methylamides:111
Reactions at the carboxy group of an amino acid𠄔amino acid salts
Authors: Barrett Graham c. 
Published: November 2023

Abstract
All the standard reactions in solution involving the carboxy group are straightforward if reagents are involved that do not affect the protected or unprotected amino group and side-chain functional groups. However, solubility problems can arise that frustrate synthetic operations with underivatized amino acids, and a number of protocols are given that illustrate ways round this problem.