"If, as we yet can scarcely doubt, there are catalytic influences which are the cause of the miasmic spread of disease, it is possible that an antiseptic substance, such as , even in vanishingly small quantities, may indeed not be without definite influence upon such processes in the air. From daily and long continued spectrum observation it would be easy to learn whether the variation in the intensity of the spectral line Naα, produced by the sodium combination in the air, is related in any degree to the appearance and the spread of endemic diseases."

"Due to economic and ecological factors, catalytic processes in the production of fine chemicals are gaining in importance, especially in the area of asymmetric catalysis (Collins et al. 1997; Breuer et al. 2004). Accordingly, the practicing chemist has three major options: transition metal catalysts (Jacobsen et al. 1999), organocatalysts (Berkessel and Gröger 2004) or enzymes (Drauz and Waldmann 2002; Liese et al. 2006). All of them have advantages and disadvantages, which means that a given type of catalysis cannot be expected to provide general solutions to all problems of relevance in academic and industrial laboratories. Therefore, research in all three approaches needs to be intensified."

"Just as the chemistry of alkenes is dominated by addition reactions, the preparation of alkenes is dominated by elimination reactions. Additions and eliminations are, in many respects, two sides of the same coin."

"As a general rule, electrophiles undergo addition reactions with alkynes much as they do with alkenes. Take the reaction of alkynes with HX, for instance. The reaction often can be stopped after addition of 1 equivalent of HX, but reaction with an excess of HX leads to a dihalide product. For example, reaction of 1-hexyne with 2 equivalents of HBr yields 2,2-dibromohexane."

"Although different kinds of chemical reactions are thus easily recognized, it has not been found very useful in general to attempt to classify reactions in a rigorous way. Nevertheless, there is one very important class of chemical reactions that deserves special study. These reactions are oxidation-reduction reactions, to which we now turn our attention."

"The investigation of redox metalloenzymes by UEM should shed new light on the mode of action because it will be possible to record electron-energy-loss spectra (Chap. 6) and to reveal oxidation states of the metal ions at active centers, even though the measurements may be complicated by the reducing environment created by the secondary electrons within the sample. These and other promising features of UEM were realized since the first UEM publication 27 (Sec. 6.1) and currently represent one of the major areas of study at Caltech."

"The synthesis of chiral compounds in enantiomerically pure form is one of the most important and one of the most challenging goals of modern organic synthesis. Any key step of synthetic importance, which leads to the creation of a stereogenic centre, requires to be studied with regard to its stereoselectivity."

"Many chiral objects, such as spiral staircases, do not have stereocenters. The same is true for many chiral molecules. Remember that the only criterion for chirality is the nonsuperimposable nature of object and mirror image."

"Now it’s time to add a third dimension to our study. Stereochemistry is the branch of chemistry concerned with the three-dimensional aspects of molecules. We’ll see on many occasions in future chapters that the exact three-dimensional structure of a molecule is often crucial to determining its properties and biological behavior."

"How do we use this idea to distinguish a chiral molecule from an achiral one? Chiral molecules cannot have a plane of symmetry."

"A compound that contains two (or, as we shall see, even more than two) stereocenters but is superimposable with its mirror image is a meso compound (mesos, Greek, middle). A characteristic feature of a meso compound is the presence of an internal mirror plane, which divides the molecule such that one half is the mirror image of the other half. For example, in 2,3-dibromobutane, the 2R center is the reflection of the 3S center."

"Chemical reactions, as exemplified by radical halogenation, can be stereoselective or not. Starting from achiral materials, such as butane, a racemic (nonstereoselective) product is formed by halogenation at C2. The two hydrogens at the methylene carbons of butane are equally susceptible to substitution, the halogenation step in the mechanism of radical bromination proceeding through an achiral intermediate and two enantiomeric transition states of equal energy. Similarly, starting from chiral and enantiomerically pure 2-bromobutane, chlorination of the stereocenter also gives a racemic product. However, stereoselectivity is possible in the formation of a new stereocenter, because the chiral environment retained by the molecule results in two unequal modes of attack on the intermediate radical. The two transition states have a diastereomeric relation, a condition that leads to the formation of products at unequal rates."

"One possible approach is to start with the racemate and separate one enantiomer from the other. This process is called the resolution of enantiomers. Some enantiomers, such as those of tartaric acid, crystallize into mirror-image shapes, which can be manually separated … However, this process is time consuming, not economical for anything but minute-scale separations, and applicable only in rare cases."

"Stereoanalysis of monosubstituted cyclohexanes involves two distinct stages: 1. Determination of the topology of the molecule 2. Assessment of the topology and its effects on the course of a reaction"

"Depending on the substitution pattern, three principal interactions dictate the conformational equilibrium: 1. The presence of a single axial substituents (butane-type gauche interaction) 2. The interaction of a pair of 1,2-diequatorial substituents (butane-type gauche interaction) 3. The interaction of a pair of cis-1,3-diaxial substituents (1,3-diaxial interaction)"

"The stereochemical course of reactions at three-, four-, and five-member rings can be reliably predicted by assuming the relative congestion of the two faces. As the ring size increases above six so does the conformational mobility and hence the uncertainty of the stereochemical outcome. Even with seven-member rings, predictions are generally difficult."

"Hydrogen combines with oxygen with great vigor. A stream of hydrogen when ignited burns in oxygen or air with a very hot, almost colorless flame (Figure 6-8), and a mixture of hydrogen and oxygen when ignited explodes with great violence. When hydrogen burns in air or oxygen, forming hydrogen oxide (water), the hydrogen is said to have been oxidized. The process is called oxidation, and oxygen is called the oxidizing agent. The tendency of hydrogen to combine with oxygen to form water is so great that the gas will even remove oxygen from many metallic oxides. Thus when a stream of hydrogen is passed over hot copper oxide, CuO, in a heated tube, the copper oxide is converted into metallic copper (Figure 6-9):CuO + H2 → Cu + H2O This reaction is described as the reduction of copper oxide by hydrogen. Hydrogen is called the reducing agent in the reaction. Copper oxide is said to have been reduced to metallic copper. In the reaction of hydrogen and copper oxide the copper oxide is the oxidizing agent. In every reaction of this sort there is a reducing agent which is oxidized and an oxidizing agent which is reduced."

"The opportunity of dedicating one’s intellectual imagination to complex problems, many of which are apt to serve the needs of a growingly needful society, must be seen as a great privilege. The means for codifying information, which is central in this regard, while rewarding the initiators (even posthumously) of what becomes a Name Reaction retains its special cultural status in assisting the forward march of our science. Name Reaction assignments have about them a significant element of intellectual history. However (and needless to say), the tracing back of all the antecedents of an idea is actually an endless process. What Name Reactions are really about is an agreed upon vocabulary,by convention, for communicating concepts in concise but human terms, befitting one of the most esthetics-intensive of scientific activities, that is, organic synthesis."

"In many cases, equilibrium lies extensively (say, more than 99.9%) on the side of the products. When this occurs, the reaction is said to go to completion."

"All reactions are described by equilibrating the concentrations of starting materials and products. On which side the equilibrium lies depends on the size of the equilibrium constant, which in turn is related to the Gibbs free energy changes ..."

"The simplest chemical reactions may be described as equilibration between two distinct species. Such processes are governed by two fundamental considerations: 1. Chemical thermodynamics, … 2. Chemical kinetics, ..."