Acidity functions, theory

The second protonation of dimethylaminopyridines and their N-oxides, all weak bases whose pK determination involves acidity function theory, yield o values in good agreement with previous values, affording thereby a check on the validity of the acidity function procedure. 

Since much work has gone into eventually disproving this mechanism for hydrogen exchange it is worth examining the soundness of the experimental data upon which the theory was based. Firstly, the log rate coefficient versus acidity function plots should have had unit slopes and the fact that they did not was attributed to salt effects. Secondly, different rate coefficients were obtained at the... 

Richardson WEI, Peng C, Bashford D, Noodleman L, Case DA (1997) Incorporating Solvation Effects into Density Functional Theory Calculation of Absolute Acidities. Int J Quantum Chem 61 207-217. 

Bakalarski, G., P. Grochowski, J. S. Kwiatkowski, B. Lesyng, and J. Leszczynski. 1996. Molecular and electrostatic properties of the N-methylated nucleic acid bases by density functional theory. Chem. Phys. 204, 301. 

The aim of this chapter is to discuss chemical reactivity and its application in the real world. Chemical reactivity is an established methodology within the realm of density functional theory (DFT). It is an activity index to propose intra- and intermolecular reactivities in materials using DFT within the domain of hard soft acid base (HS AB) principle. This chapter will address the key features of reactivity index, the definition, a short background followed by the aspects, which were developed within the reactivity domain. Finally, some examples mainly to design new materials related to key industrial issues using chemical reactivity index will be described. I wish to show that a simple theory can be state of the art to design new futuristic materials of interest to satisfy industrial needs. 

Our goal in this chapter is to help you understand the equilibrium systems involving acids and bases. If you don t recall the Arrhenius acid-base theory, refer to Chapter 4 on Aqueous Solutions. You will learn a couple of other acid-base theories, the concept of pH, and will apply those basic equilibrium techniques we covered in Chapter 14 to acid-base systems. In addition, you will need to be familiar with the log and 10 functions of your calculator. And, as usual, in order to do well you must Practice, Practice, Practice. 

The above-mentioned concept of the synthesis of carboxylic acid functional hyperbranched polyesteramides is not limited to cyclic anhydrides as building blocks. It can be carried out with diisopropanolamine and any dicarboxylic acid as well. The same ratios as written above and calculated in Scheme 1 have been applied in the synthesis of carboxylic acid functional hyperbranched polyesteramides starting from adipic acid and diisopropanolamine. The first one (ratio 2.3 1) gelates as expected, the second one (ratio adipic acid diisopropanolamine 3.2 1) affords the expected product. Again, with GPC the amount of free adipic acid detected is in good agreement with theory (Fig. 17). 

A model system consisting of methyloxirane, formate, and formic acid has been used to study the nucleophile-catalysed and nucleophile- and acid-catalysed opening of an epoxide ring by applying ab initio quantum mechanical calculations [up to the MP4(SDQ)/6-31- -G //MP2/6-31- -G" level] and also density functional theory... 

Theoretical evidence [Hartree-Fock (RHF) calculations and density functional theory] has been obtained for a concerted mechanism of oxirane cleavage and A-ring formation in oxidosqualene cyclization. A common concerted mechanistic pathway has been demonstrated for the acid-catalysed cyclization of 5,6-unsaturated oxiranes in chemical and enzymic systems. For example, the conversion of (24) into (26) proceeds via (25) and not via a discrete carbocation (27). Kinetic studies and other evidence are presented for various systems. 

Density functional theory calculations (B3LYP/6-31G level) have provided an explanation for the stereodivergent outcome of the Staudinger reaction between acyl chlorides and imines to form 2-azetidinones (/3-lactams). When ketene is formed prior to cycloaddition, preferential or exclusive formation of ct5-j6-lactam (50) is predicted. If, however, the imine reacts directly with the acid chloride, the step that determines the stereochemical outcome is an intramolecular 5n2 displacement, and preferential or exclusive formation of trans isomer (51) is predicted. These predictions agree well with the experimental evidence regarding the stereochemical outcome for various reactants and reaction conditions. 

A new transition-state-searching algorithm was used to determine the mechanism for methanol condensation to form dimethyl ether within the microporous environment of the zeolite, chabazite, using periodic boundary conditions and density functional theory. An acid site in the zeolite produces MeOH2+ for nucleophilic attack by a second adsorbed MeOH molecule. 

With the aid of density functional theory, the ZnCl2 acceleration of the Simmons-Smith reaction of ethylene and allyl alcohol has been investigated. A pathway involving direct Lewis acid acceleration of the leaving halogen atom (327) was found to be a more facile process than the more popular pathway involving 1,2-chlorine migration (328). 

It now remains to explain why this tautomeric equilibrium shifts towards dominant O-protonation in concentrated and anhydrous acid. The reasons for the changeover can best be understood in terms of the developments in the theory of acidity functions, which have been outlined on page 293. Cation solvation must be taken into account in considering the tautomeric equilibrium (33). 

With reference to a solvent, this term is usually restricted to Brpnsted acids. If the solvent is water, the pH value of the solution is a good measure of the proton-donating ability of the solvent, provided that the concentration of the solute is not too high. For concentrated solutions or for mixtures of solvents, the acidity of the solvent is best indicated by use of an acidity function. See Degree of Dissociation Henderson-Hasselbalch Equation Acid-Base Equilibrium Constants Bronsted Theory Lewis Acid Acidity Function Leveling Effect... 

DEGREE OF DISSOCIATION HENDERSON-HASSELBALCH EQUATION ACID-BASE EQUILIBRIUM CONSTANTS BR0NSTED THEORY LEWIS ACID ACIDITY FUNCTION LEVELING EFFECT ACIDITY FUNCTION ACID-LABILE SULFIDES ACID PHOSPHATASE ACONITASE... 

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