4.2.8. Reductive Coupling 3109 5. Reaction of Aromatic Compounds 3110 5.1. Electrophilic Substitutions 3110 5.2. Radical Substitution 3111 5.3. Oxidative Coupling 3111 5.4. Photochemical Reactions 3111 6. Reaction of Carbonyl Compounds 3111 6.1. Nucleophilic Additions 3111 6.1.1. Allylation 3111 6.1.2. Propargylation 3120 6.1.3. Benzylation 3121 6.1.4. Arylation/Vinylation 3121 6.1.5. Alkynylation 3121 6.1.6. Alkylation 3121 6.1.7. Reformatsky-Type Reaction 3122 6.1.8. Direct Aldol Reaction 3122 6.1.9. Mukaiyama Aldol Reaction 3124 6.1.10. Hydrogen Cyanide Addition 3125 6.2. Pinacol Coupling 3126 6.3. Wittig Reactions 3126 7. Reaction of R,â-Unsaturated Carbonyl Compounds 3127

Organic Reactions in Aqueous Media with a Focus on Carbon−Carbon Bond Formations: A Decade Update

Stereoselective organic reactions in water.

5.7. [32π + 32σ] Cycloadditions 74 5.8. [44π + 22π] Cycloadditions 75 6. Seven-Membered Ring Formation 78 6.1. [44π + 32σ] Cycloadditions 78 6.2. [52π+2σ + 22π] Cycloadditions 79 7. Eight-Membered Ring Formation 79 7.1. [22π + 22π + 22π + 22π] Cycloadditions 80 7.2. [44π + 22π + 22π] Cycloadditions 80 7.3. [44π + 44π] Cycloadditions 81 7.4. [66π + 22π] Cycloadditions 83 8. Ten-Membered Ring Formation 85 9. Conclusion and Remarks 87

Transition Metal-Mediated Cycloaddition Reactions

NMR Studies of Cyclodextrins and Cyclodextrin Complexes

This article presents evidence for the existence of a specific linear relationship between the entropy change and the enthalpy change in a variety of processes of small solutes in water solution. The processes include solvation of ions and nonelectrolytes, hydrolysis, oxidation–reduction, ionization of weak electrolytes, and quenching of indole fluorescence among others. The values of the proportionality constant, called the compensation temperature, lie in a relatively narrow range, from about 250 to 315 °K, for all these processes. Such behavior can be a consequence of experimental errors but for a number of the processes the precision of the data is sufficient to show that the enthalpy–entropy compensation pattern is real. It is tentatively concluded that the pattern is real, very common and a consequence of the properties of liquid water as a solvent regardless of the solutes and the solute processes studied. As such the phenomenon requires that theoretical treatments of solute processes in water be expanded by inclusion of a specific treatment of the characteristic of water responsible for compensation behavior. The possible bases of the effect are proposed to be temperature-independent heat-capacity changes and/or shifts in concentrations of the two phenomenologically significant species of water. The relationship of these alternatives to the two-state process of water suggested by spectroscopic and relaxation studies is examined. The existence of a similar and probably identical relationship between enthalpy and entropy change in a variety of protein reactions suggests that liquid water plays a direct role in many protein processes and may be a common participant in the physiological function of proteins. It is proposed that the linear enthalpy–entropy relationship be used as a diagnostic test for the participation of water in protein processes. On this basis the catalytic processes of chymotrypsin and acetylcholinesterase are dominated by the properties of bulk water. The binding of oxygen by hemoglobin may fall in the same category. Similarities and differences in the behavior of small-solute and protein processes are examined to show how they may be related. No positive conclusions are established, but it is possible that protein processes are coupled to water via expansions and contractions of the protein and that in general the special pattern of enthalpy–entropy compensation is a consequent of the properties of water which require that expansions and contractions of solutes effect changes in the free volume of the nearby liquid water. It is shown that proteins can be expected to respond to changes in nearby water and interfacial free energy by expansions and contractions. Such responses may explain a variety of currently unexplained characteristics of protein solutions. More generally, the enthalpy–entropy compensation pattern appears to be the thermodynamic manifestation of “structure making” and “structure breaking,” operationally defined terms much used in discussions of water solutions. If so, the compensation pattern is ubiquitous and requires re-examination of a large body of molecular interpretations derived from quantitative studies of processes in water. Theories of processes in water may have to be expanded to accommodate this aspect of water behavior.

Enthalpy-entropy compensation phenomena in water solutions of proteins and small molecules: a ubiquitous property of water.

Second-order rate constants and isobaric activation parameters for the intermolecular Diels-Alder reactions of cyclopentadiene with alkyl vinyl ketones (2a,b) and 5-substituted-1,4-naphthoquinones (3a-c) as well as for the intramolecular Diels-Alder reaction of N-furfuryl-N-methylmaleamic acid (4) were determined in water, monohydric alcohols, and highly aqueous solutions containing monohydric alcohols and other organic cosolvents. The intermolecular as well as the intramolecular Diels-Alder reaction are characterized by large rate accelerations upon going from an organic solvent to water as the reaction medium. A model for solvation effects on rate constants for Diels-Alder reactions in aqueous solutions is developed. The typical, huge rate enhancements for Diels-Alder reactions in water and in highly aqueous binary mixtures are significantly sensitive to substituent effects and are discussed in terms of enforced pairwise hydrophobic interactions between diene and dienophile.

Diels-Alder reactions in aqueous solutions. Enforced hydrophobic interactions between diene and dienophile

https://pure.rug.nl/ws/files/26440021/2001ChemCommEngberts.pdf

Understanding organic reactions in water: from hydrophobic encounters to surfactant aggregates

Herein we report a new endeavor to frame a picture of the hydration of monosaccharides as a function of their stereochemistry. To this end we have measured pseudo-first-order rate constants for the water-catalyzed hydrolysis of 1-benzoyl-3-phenyl-1,2,4-triazole in aqueous solutions in the presence of 0-1.00 mol.kg -1 of a series of aldohexoses, ketohexoses and aldopentoses

Stereochemical aspects of the hydration of carbohydrates - kinetic medium effects of monosaccharides on a water-catalyzed hydrolysis reaction

Calorimetric titration plots for deaggregation of micelles formed
by alkylpyridinium and alkyltrimethylammonium surfactants are
classified into three types, A, B and C, depending on the shape of the
plot of the enthalpy of dilution as a function of surfactant
concentration. For Type A plots the recorded heat of injection
q changes sharply between two parts of the titration curve
over which the recorded heats are effectively independent of the
composition of the solution in the sample cell. For Type B plots, the
change is less sharp and both parts of the plot show dependences of
heat q on solution composition, a pattern accounted for in
terms of solute–solute interactions. Type C plots are
complicated, in that no sharp change in q is recorded, the
complexity of the plots being accounted for in terms of
micelle–monomer equilibria over a range of surfactant
concentrations and related enthalpies of deaggregation.

/pdf/classification-of-calorimetric-titration-plots-for-3pv2kx7e10.pdf

Classification of calorimetric titration plots for alkyltrimethylammonium and alkylpyridinium cationic surfactants in aqueous solutions

Rate constants for the hydrolysis of 1-benzoyl-3-phenyl-1,2,4-triazole in aqueous solutions of carbohydrates have been measured as a function of molality and nature of added mono- and disaccharides. The kinetic medium effects induced by the carbohydrates originate from hydration sphere overlap effects. The results are analyzed using the additivity principle and reveal specificity in the stereochemical aspects of hydration. The major effect determining the hydration of a monosaccharide appears to be the position of the OH(4) group in conjunction with OH(2). The position of the carbonyl function and the number of equatorial groups present in the molecule are of minor importance. The experimentally obtained G(C) values, which are representative of the interaction between the carbohydrate and the initial state and activated complex for the hydrolysis reaction, show that the hydration of the carbohydrates is mainly determined by the methine moieties. The G(CHOH,endo) values obtained for the dominant conformers in solution point to a similar conclusion. With an increase in compatibility of the carbohydrate molecule with the three-dimensional hydrogen-bond structure of water, the hydroxy groups become less important in determining carbohydrate-solute interactions. This might be important in molecular recognition, since under these conditions the carbohydrates are recognized as hydrophobic moieties. For disaccharides the medium effects are larger than expected on the basis of the medium effect of two monosaccharide subunits. We suggest that this is caused by a cooperativity effect, which makes the methine moieties even more dominant in governing the hydration characteristics. The G(C) values reveal that the type of linkage in the disaccharide molecule hardly influences the kinetic medium effect. Only when one of the monosaccharide subunits has an axial OH(4) or when there is a 1-3 type of linkage between the moieties is a significantly different G(C) found. It is suggested that the compatibility of the carbohydrates with the three-dimensional hydrogen-bond structure of water largely depends on the compatibility of the next nearest neighbor oxygens of the carbohydrate molecule with the nearest or next nearest neighbor oxygens of liquid water.

Michael J. Blandamer

Papers

Diels-Alder reactions in aqueous solutions. Enforced hydrophobic interactions between diene and dienophile

Understanding organic reactions in water: from hydrophobic encounters to surfactant aggregates

Stereochemical aspects of the hydration of carbohydrates - kinetic medium effects of monosaccharides on a water-catalyzed hydrolysis reaction

Classification of calorimetric titration plots for alkyltrimethylammonium and alkylpyridinium cationic surfactants in aqueous solutions

Stereochemical aspects of hydration of carbohydrates in aqueous-solutions .2. kinetic medium effects