Thermodynamics basics formation

The reasons for the reluctance of the diamines to undergo protonation is due to the inaccessibility of the basic sites. The high thermodynamic basicity is probably due to a combination of the formation of a strong intramolecular hydrogen bond and to unfavourable lone pair interactions in the diamines that cannot be relieved by solvation. 

The Y-T equation has been used to analyse the substituent effects on carbocation formation equilibria in the gas phase. These correlations are compared with those for the kinetic substituent effects in the corresponding solution phase solvolyses in Table 17 and substituent effects on thermodynamic basicities of carbonyl groups in both phases are compared in Tables 18 and 19. 

The thermodynamics of formation of BF3 complexes has been extensively investigated. However, the thermodynamic data collected in reviews prior to 1970 [2-4] do not allow the construction of homogeneous Lewis basicity or affinity scales because they do not refer to the same reaction and/or to the same medium. In fact, the types of reactions investigated... 

The idea of kinetic versus thermodynamic control can be illustrated by discussing briefly the case of formation of enolate anions from unsymmetrical ketones. This is a very important matter for synthesis and will be discussed more fully in Chapter 1 of Part B. Most ketones, highly symmetric ones being the exception, can give rise to more than one enolate. Many studies have shown tiiat the ratio among the possible enolates that are formed depends on the reaction conditions. This can be illustrated for the case of 3-methyl-2-butanone. If the base chosen is a strong, sterically hindered one and the solvent is aptotic, the major enolate formed is 3. If a protic solvent is used or if a weaker base (one comparable in basicity to the ketone enolate) is used, the dominant enolate is 2. Enolate 3 is the kinetic enolate whereas 2 is the thermodynamically favored enolate. 

The reactivity of the methyl group in 4-methylcinnoline ethiodide indicates that the structure of this compound is 5, and this evidence has also been interpreted to mean that N-1 is the basic group in cinnolines. However, evidence of this type is only indicative since the formation of quaternary salts is subject to kinetic control, whereas protonation yields predominantly the thermodynamically more stable cation. The quinazoline cation has been shown to exist in the hydrated, resonance-stabilized form 6 7 by ultraviolet spectro-... 

Standard retrosynthetic manipulation of PGA2 (1) converts it to 5 (see Scheme 2). A conspicuous feature of the five-membered ring of intermediate 5 is the /(-keto ester moiety. Retrosynthetic cleavage of the indicated bond in 5 furnishes triester 6 as a potential precursor. Under basic conditions and in the synthetic direction, a Dieck-mann condensation4 could accomplish the formation of a bond between carbon atoms 9 and 10 in 6 to give intermediate 5. The action of sodium hydroxide on intermediate 5 could then accomplish saponification of both methyl esters, decarboxylation, and epi-merization adjacent to the ketone carbonyl to establish the necessary, and thermodynamically most stable, trans relationship between the two unsaturated side-chain appendages. 

In our retro-synthetic analysis, we envisioned the pyrrolidinylethanol side chain could be installed via the Ullmann ether formation or the analogous reachons from the aryl-iodide functional group. The key intermediate 9 (cis) in the Medicinal Chemistry route was not stable under strongly acidic or basic conditions since it was easily isomerized to the thermodynamically more stable trans-isomer 9a via... 

There are also voices critical of the rTCA cycle Davis S. Ross has studied kinetic and thermodynamic data and concludes that the reductive, enzyme-free Krebs cycle (in this case the sequence acetate-pyruvate-oxalacetate-malate) was not suitable as an important, basic reaction in the life evolution process. Data on the Pt-catalysed reduction of carbonyl groups by phosphinate show that the rate of the reaction from pyruvate to malate is much too low to be of importance for the rTCA cycle. In addition, the energy barrier for the formation of pyruvate from acetate is much too high (Ross, 2007). 

The basic principle of solution calorimetry is simple. In one experiment the enthalpy of solution of, for example, LaA103(s) [32] is measured in a particular solvent. In order to convert this enthalpy of solution to an enthalpy of formation, a thermodynamic cycle, which gives the formation reaction... 

Cyclobutane has not been polymerised cationically (or by any other mechanism). Thermochemistry tells us that the reason is not thermodynamic it is attributable to the fact that the compound does not possess a point of attack for the initiating species, the ring being too big for the formation of a non-classical carbonium ion analogous to the cyclopropyl ion, so that there is no reaction path for initiation. The oxetans in which the oxygen atom provides a basic site for protonation, are readily polymerizable. Methylenecyclobutane polymerises without opening of the cyclobutane ring [72, 73]. 

Chemical templates are being increasingly employed for the development of dynamic combinatorial libraries (DCL) [94-98]. These (virtual) libraries of compounds are produced from all the possible combinations of a set of basic components that can reversibly react with each other with the consequent potential to generate a large pool of compounds. Because of the dynamic equilibria established in a DCL, the stabilization of any given compound by molecular recognition will amplify its formation. Hence the addition of a template to the library usually leads to the isolation of the compound that forms the thermodynamically more stable host-guest complex (see Scheme 37). 

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