INDEX decarboxylation

Another example of the use of transition state pKa values has been provided by Pollack (1978). From the rate constants for the decarboxylation of substituted a,a-dimethylbenzoylacetic acids ([37] — [38]) and their anions, he calculated pK for reaction of the acids (Table A6.2). The values vary significantly with the phenyl substituent (p = +1.7), much more so than the p/(a values of the substrate acids (p = +0.2). This difference is consistent with the proton being much closer to the phenyl group in the transition state than in the initial state, and it may even denote a relatively late transition state (Pollack, 1978). However, from the pKa values of the reactant acids (approximately 3.4), the transition states (approximately 4.4), and the enol product (11.8) (Pruszynski et al., 1986), the Leffler index... 

The correlation of the rates of decarboxylation of the difluoro diethyl lactone with solubdity parameter shows that the rate increases dramatically as the value of 8 increases. In fact, there was a factor of almost 500 difference in the rate constants depending on the solvent chosen. This is in agreement with the conclusion that the transition state for the reaction carried out in solution involves a substantial separation of charge. Furthermore, Figure 5.11 shows that the solubihty parameter can be a useful index for assessing the role of the solvent in a reaction of a greatly different type than those described earlier in this chapter. The entropy of activation for the reaction was reported... 

The rate at which Cl of glucose, as compared with C6, is converted to CO2 is used as an index for the quantitative importance of different pathways of carbohydrate metabolism. In Glycolysis (see). Cl and C6 become equilibrated at the level of the triose phosphates. Subsequent oxidation and decarboxylation in the tricarboxylic acid cycle therefore results in equal rates of production of COj from [l- C]glu-cose and [6- C]gjucose. 

Of the biogenic amines produced on the decarboxylation of amino acids (cf. 10.2.8.3), histamine, tyramine, putrescine and cadaverine have been identified in beef and pork. Since these substances are microbial metabolic products, they were the proposed indicators of microbial quality and were listed in the biogenic amine index (BAI = concentration of the four amines in mg/kg). A BAI value of <5 indicates clean meat, 5-20... 

This index does not Hst generally used transformations such as cycloaddition(s), cyclocondensation, thermolysis, photolysis, photoisomerization, oxidation, reduction, decarboxylation, valence tautomerism, metalation, C-C-coupling reactions, metathesis, etc. 

The authors have found that the ROP of TeMC initiated with H2O or a primary alcohol (e.g., butyl alcohol) in the presence other Bronsted acids such as HCl Et20 proceeded without decarboxylation to give linear poly(TeMC) with Mn= 1000-10 000 and a narrow dispersion index ( 1.15). They postulated that the key feature of this polymerization is the appropriate acidity of the protonic acid, which should be not as high to polymerize the monomer by itself but sufficient to activate the monomer. ... 

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