Reaction thermodynamic product

The two main principles involved in establishing conditions for performing a reaction are chemical kinetics and thermodynamics. Chemical kinetics is the study of rate and mechanism by which one chemical species is converted to another. The rate is the mass in moles of a product produced or reactant consumed per unit time. The mechanism is the sequence of individual chemical reaction whose overall result yields the observed reaction. Thermodynamics is a fundamental of engineering having many applications to chemical reactor design. 

In general bromination of 20-ketones is directed to the introduction of functionality at C-21. However, on occasion 17-bromo compounds are required for dehydrobromination to A -20-ketones, although these are generally obtained in other ways. Kinetic enolization of a 20-ketone gives the A °-enol, whereas the thermodynamic product is the A kjsomer. An interesting enolate trapping reaction has been used recently to prepare 16-methyl-A -20-ketones ... 

Draw the other stereoisomer that might have been obtained from syn addition of hydrogen to each alkene. Is the observed product for each addition also the thermodynamic product Compare energies for alkene A+ H2 observed and not observed and alkene B+H2 observed and not observed. What structural factors seem to be responsible for the relative stabilities of the two products of each hydrogenation reaction ... 

Chemists have estabhshed that a Dieckmann condensation will not succeed unless the final keto-ester product is deprotonated by a base. In our example, this would be a reaction between EtO" and the keto-ester (it is necessary, therefore, to use excess EtO ). What reaction products are generated by this proton transfer Obtain the energies of the reactants and products, and calculate the energy for this final proton transfer. Is this reaction thermodynamically favorable or unfavorable Does this step make the overall condensation reaction favorable or unfavorable ... 

Chemical reactions often yield entirely different product distributions depending on the conditions under which they are carried out. In particular, high temperatures and long reaction times favor the most stable ( thermodynamic ) products, while low temperatures and short reaction times favor the most easily formed ( kinetic ) products. 

Thermodynamically-Controlled Reaction. A reaction the product ratio for which is determined solely by the relative thermochemical stabilities of the different products (product formation must be reversible, or separate low-energy pathways interconnecting the products must exist). 

For the kinetically controlled formation of 1,3-disubstituted tetrahydro-P-carbolines, placing both substituents in equatorial positions to reduce 1,3-diaxial interactions resulted in the cw-selectivity usually observed in these reactions." Condensation reactions carried out at or below room temperature in the presence of an acid catalyst gave the kinetic product distribution with the cw-diastereomer being the major product observed, as illustrated by the condensation of L-tryptophan methyl ester 41 with benzaldehyde. At higher reaction temperatures, the condensation reaction was reversible and a thermodynamic product distribution was observed. Cis and trans diastereomers were often obtained in nearly equal amounts suggesting that they have similar energies."... 

The parent TMM precursor (1) reacts with tropones (117) to give reasonable yields of the bridged [4.3.1]decanones (118) [43]. Various substituted TMMs also cycloadd to tropone with regioselectivity similar to that of the corresponding [3+2] cases [20, 43]. Addition of MesSnOAc as a co-catalyst also leads to yield improvement [16]. In the case of a phenyl-substituted tropone and a methyl-TMM, performing the reaction under high pressure favors the formation of kinetic products (119) and (120) over the thermodynamic product (121) [11]. 

Halogenation of steroid 3-ketones can lead to complicated mixtures by virtue of the fact that the kinetic enol leads to 3 halo products, whereas the thermodynamic product is that halogenated at the 4 position. Carefully controlled reaction of the 5a-androstanolone with chlorine thus leads to the 2a-chloro derivative (29). Reaction of that intermediate with O(p-nitrophenyl)-hydroxylamine affords the androgenic agent ni stremine acetate (30). ... 

Taft equation, 229-230 Temperature, effect on rate, 156-160 Temperature-jump method, 256 Termination reaction, 182 Thermodynamic products, 59 Three-halves-order kinetics, 29... 

In the reaction with butanone, an equilibrium between the CH3-activated complex and the CH2-activated complex is observed and it is revealed that the former is a thermodynamic product and the latter is a kinetic product. These results indicate that the relative reactivity of the C-H bonds is in the order of 2>1>3, and the large and electron-withdrawing substituents retard the reaction. A plausible mechanism is shown in Scheme 63. When the oxy-... 

The thermodynamic product distribution in the Friedel-Crafts methylation (Scheme 20) is in contrast to the kinetic distribution. The reaction kinetically shows the ortho and para orientations. Thermodynamic stabilities of the products prefer the meta isomer as a major product. 

Many opportunities conversely are supported by reversible reactions of QM despite the noted complications. One example includes the synthesis and chiral resolution of binaphthol derivatives by two cycles of QM formation and alkylation.77 The reversibility of QM reaction may also be integrated in future design of self-assembling systems to provide covalent strength to the ultimate thermodynamic product. To date, QMs have already demonstrated great success in supporting the opposite process, spontaneous disassembly of dendrimers (Chapter 5). 

Fig. 33. Newton diagram in velocity space for the reaction Y + cis-2-butene at Ecoll = 26.6 kcal/mol. Circles represent the maximum CM velocity constraints on the indicated metal-containing fragment from the various product channels based on reaction thermodynamics as shown in Fig. 32 and momentum conservation.

For reversible reactions one normally assumes that the observed rate can be expressed as a difference of two terms, one pertaining to the forward reaction and the other to the reverse reaction. Thermodynamics does not require that the rate expression be restricted to two terms or that one associate individual terms with intrinsic rates for forward and reverse reactions. This section is devoted to a discussion of the limitations that thermodynamics places on reaction rate expressions. The analysis is based on the idea that at equilibrium the net rate of reaction becomes zero, a concept that dates back to the historic studies of Guldberg and Waage (2) on the law of mass action. We will consider only cases where the net rate expression consists of two terms, one for the forward direction and one for the reverse direction. Cases where the net rate expression consists of a summation of several terms are usually viewed as corresponding to reactions with two or more parallel paths linking reactants and products. One may associate a pair of terms with each parallel path and use the technique outlined below to determine the thermodynamic restrictions on the form of the concentration dependence within each pair. This type of analysis is based on the principle of detailed balancing discussed in Section 4.1.5.4. 

If a reaction can give multiple products, that obtained first (the kinetic product) is not necessarily the most stable (the thermodynamic product). The kinetic product will be in equilibrium with the starting materials but not necessarily with the thermodynamic product. 

The 1,3-dipolar cycloadditions of nitrones (551), (595), (614), (615) and their enantiomers (595 ent), (614 ent), (615 ent) (Fig. 2.40) to a.p-unsaturated y-lactones, such as achiral D7 g and D-glycero D7 h, provide an interesting example of double asymmetric inductions. The reactions are kinetically controlled. However, on heating and at longer reaction times, the reversibility of the cycloaddition (595 + D7 h) was observed, and the presence of a more stable thermodynamic product (620) was detected. Moreover, in the case of lactone D7 h, a... 

Low-temperature 31P NMR studies showed that the reaction of (PCP)Ir with nitrobenzene leads to three products of the type (PCP)Ir(aryl)H and meta- and /> ra-additions are kinetically favored. However, refluxing the trans-isomer afforded the f-product, designated the thermodynamic product. Nevertheless, chelation to the metal still remains an important regiochemical factor in these reactions, which will be termed chelation controlled or directed hereafter.92... 

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