Products thermodynamic

Pyrolysis of diketene at temperatures greater than 400°C gives two molecules of ketene. This method has been used iadustriaHy. At present there is no method to convert diketene efftciendy iato aHene [463-49-0] and CO2, the thermodynamic products. 

The a-form, which crystallines as the kinetic product, is the commercial form of ammonium pentaborate tetrahydrate and the P-form is the thermodynamic product but is slow to crystalline. Its heat capacity has been measured over a broad temperature range (85). Solubihty data are given ia Table 9 and pH data ia Table 10. 

No blocking group was utilized in the Schering-Hoffman-La Roche approach instead, advantage was taken of the fact that the 7a-bromo-5a-6-ketone is the thermodynamic product ... 

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 ... 

The product of nucleophilic attack can be anticipated by examining the lowest-unoccupied molecular orbital (LUMO) on protonated cyclopentene oxide. From which direction (top or bottom) would a nucleophile be more likely to approach each epoxide carbon in order to transfer electrons into this orbital Explain. Does one carbon contribute more to the LUMO, or is the orbital evenly spread out over both epoxide carbons Assuming that LUMO shape dictates product stereochemistry, predict which stereoisomers will be obtained, and their approximate relative amounts. Is the anticipated kinetic product also the thermodynamic product (Compare energies of 1,2-cyclopentanediol stereoisomers to tell.)... 

Is your predicted product also the thermodynamic product Energies for eis and trans-3,4-dimethyl-eyelobutene are available. 

Examine transition states leading to para and meta adducts 2-methoxybutadiene+acrylonitrile para and meta) as well as the adducts themselves (l-methoxy-4-cyanocyclohexene and l-methoxy-5-cyanocyclohexene). What should the kinetic product be Is this in line with your expectations based on orbital interactions Is this also the thermodynamic product ... 

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. 

Are the kinetic and thermodynamic products the same If not, describe conditions which will favor the endo adduct. The exo adduct. 

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). ... 

Figure 14.6 Energy diagram for the electrophilic addition of HBr to 1,3-butadiene. The 1.2 adduct is the kinetic product because it forms faster, but the 1,4 adduct is the thermodynamic product because it is more stable.

In Sections 5.2 and 5.3 it was shown that experimental data are consistent with a direct rearrangement of the (Z)- to the (ii)-diazohydroxide rather than with a recombination after a primary dissociation of the (Z)-isomer into a diazonium ion. Positive evidence for direct formation of the (ii)-diazohydroxide from the diazonium ion and a hydroxide ion (or water) is still lacking (see Scheme 5-15 in Sec. 5.2). For diazo ethers, however, Broxton and Roper (1976) came to the conclusion that there is no direct (Z) >(E) conversion, but rather that in the system ArNj + OCH3/(Z)-diazo ether/(Zi)-diazo ether the (Z)-ether is the kinetically determined product and the (iE )-isomer the thermodynamic product, as shown in Scheme 6-3. 

Clearly, this scheme produces the various products in relative yields [Pi] [Pi] [P ], which correspond to the ratios of rate constants Jkj k2 kn. The product yields can be measured at completion or at any midway point. Products formed in such ratios are said to be kinetic products, as distinct from thermodynamic products. The latter would be present in those ratios that would prevail when equilibrium had been established among Pi, Pi, etc. 

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. 

The obvious choice for a reagent is again a sulphur ylid, but how are we to control the regioselectivity of the addition The more reactive sulphur ylids, notably (26) and (27), add directly to the carbonyl group (kinetic control, cf p T 117 ) giving epoxides (29) while the more stable ylid (28), which combines the anion-stabilisations of (26) and (27), adds reversibly and gives the thermodynamic product (25). 

Cyclisation and decarboxylation gave ketone (48) which was reduced to a mixture of (47) and (45), The highest ratio of transjais was achieved with (l-PrO)gAi, which normally favours the thermodynamic product (p T 101). 

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). 

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