Kinetic isotope effect table

The cases of pentamethylbenzene and anthracene reacting with nitronium tetrafluoroborate in sulpholan were mentioned above. Each compound forms a stable intermediate very rapidly, and the intermediate then decomposes slowly. It seems that here we have cases where the first stage of the two-step process is very rapid (reaction may even be occurring upon encounter), but the second stages are slow either because of steric factors or because of the feeble basicity of the solvent. The course of the subsequent slow decomposition of the intermediate from pentamethylbenzene is not yet fully understood, but it gives only a poor yield of pentamethylnitrobenzene. The intermediate from anthracene decomposes at a measurable speed to 9-nitroanthracene and the observations are compatible with a two-step mechanism in which k i k E and i[N02" ] > / i. There is a kinetic isotope effect (table 6.1), its value for the reaction in acetonitrile being near to the... 

Other workers have concluded that the transition state for the Menshutkin reaction is late with more nitrogen-alpha carbon bond formation than alpha carbon-leaving group bond rupture. For instance, Harris and coworkers51 found that the secondary alpha deuterium kinetic isotope effects (Table 8) decreased when a poorer nucleophile was used in the S v 2 reactions between 3,5-disubstituted pyridines and methyl iodide in 2-nitropropane at 25 °C (equation 38, Table 8). 

The secondary alpha deuterium and primary leaving group nitrogen kinetic isotope effects (Table 16) were determined for the ion-pair Sw2 reactions between sodium thiophenoxide and benzyldimethylphenylammonium nitrate in DMF at 0 °C60 and in methanol at 20 "C64 to learn how a change in solvent affects the structure of the Sp2 transition state. 

Two other points should be noted (a) Rate constants for the reaction of OH radicals with ethene-d4 and ethene-h4 (151) and with propene-d5 and propene-h5 (91, 185) showed a small ( 15%) kinetic Isotope effect (Table 3a). The data for propene-d5 and propene-h5 (91, 185) were advanced by Stuhl (185) as evidence for OH-radlcal-addition being the major reaction pathway. However, Gutman and co-workers (158) have pointed out that If the abstraction reaction occurred, It would be fast and have little or no activation energy. Hence a significant kinetic Isotope effect would not be expected for H-atom abstraction, as. Indeed,... 

The primary kinetic isotope effects (Table 3, p. 192) have been listed in order of predicted decreasing extent of proton transfer within a given solvent. Proton... 

Molecular Dynamics Simulation of Kinetic Isotope Effects Table 21.1... 

Melander first sought for a kinetic isotope effect in aromatic nitration he nitrated tritiobenzene, and several other compounds, in mixed acid and found the tritium to be replaced at the same rate as protium (table 6.1). Whilst the result shows only that the hydrogen is not appreciably loosened in the transition state of the rate-determining step, it is most easily understood in terms of the S 2 mechanism with... 

Table 10.6. Kinetic Isotope Effects in Some Electrophilic Aromatic Substitution Reactions...

A kinetic isotope effect that is a result of the breaking of the bond to the isotopic atom is called a primary kinetic isotope effect. Equation (6-88) is, therefore, a very simple and approximate relationship for the maximum primary kinetic isotope effect in a reaction in which only bond cleavage occurs. Table 6-5 shows the results obtained when typical vibrational frequencies are used in Eq. (6-88). Evidently the maximum isotope effect is predicted to be very substantial. 

Table 6-5. Calculated Hydrogen/Deuterium Primary Kinetic Isotope Effects" ...

The kinetic isotope effect with 2-naphthol-8-sulfonic acid in Table 12-3 was reported only three years later (Ernst et al., 1958) based on a suggestion of P.D. Bartlett. That paper was publication no. 1 of the first-mentioned author. At that time he was an ETH student. He obtained the Nobel Prize 33 years later for his work on NMR spectroscopy ... 

The conclusions from the foregoing studies with phenol have been challenged by Challis and Lawson121, who find that rates of nitrosation (shown graphically) pass through a maximum at about 8 M perchloric acid, and also that the reaction shows a large primary kinetic isotope effect at 0.7 °C (Table 27). Hence loss of a... 

The kinetics of the decarboxylation of anthranilic acid have recently been examined. Earlier, an investigation of the decarboxylation of anthranilic acid in aqueous or acidic solution at 100 °C gave a C12 C13 value of 108.02 after 72 % reaction in 1.0 M sulphuric acid compared with 108.5 from complete decarboxylation, so that there is virtually no kinetic isotope effect for this compound646. First-order rate coefficients are given in Table 218 and from the variation of rate... 

Kinetic data exist for all these oxidants and some are given in Table 12. The important features are (i) Ce(IV) perchlorate forms 1 1 complexes with ketones with spectroscopically determined formation constants in good agreement with kinetic values (ii) only Co(III) fails to give an appreciable primary kinetic isotope effect (Ir(IV) has yet to be examined in this respect) (/ ) the acidity dependence for Co(III) oxidation is characteristic of the oxidant and iv) in some cases [Co(III) Ce(IV) perchlorate , Mn(III) sulphate ] the rate of disappearance of ketone considerably exceeds the corresponding rate of enolisation however, with Mn(ril) pyrophosphate and Ir(IV) the rates of the two processes are identical and with Ce(IV) sulphate and V(V) the rate of enolisation of ketone exceeds its rate of oxidation. (The opposite has been stated for Ce(IV) sulphate , but this was based on an erroneous value for k(enolisation) for cyclohexanone The oxidation of acetophenone by Mn(III) acetate in acetic acid is a crucial step in the Mn(II)-catalysed autoxidation of this substrate. The rate of autoxidation equals that of enolisation, determined by isotopic exchange , under these conditions, and evidently Mn(III) attacks the enolic form. 

Table 4-2. Computed and experimental primary 12C/13C and secondary 14N/15N kinetic isotope effects for the decarboxylation of N-methyl picolinate at 25 °C in water...

The kinetic isotope effect proves the attack of ozone on the C—H bond and consequently the C—D bond of the oxidized compound. The values of the kinetic isotope effect (kH/kD) are collected in Table 3.6. 

The rate constants of the reaction of PINO with hydrocarbons and alcohols, and the values of kn/kn are given in Table 5.7. A very high kinetic isotope effect is seen in this reaction. 

TABLE 9. The primary hydrogen-deuterium kinetic isotope effects for the hydrogen transfer reactions between alkyl radicals and tributyltin hydride (deuteride)... 

TABLE 11. The primary hydrogen-tritium kinetic isotope effects found in the reactions between various alkyl radicals and tributyltin hydride and tributyltin hydride-t... 

TABLE 16. The hydrogen-deuterium kinetic isotope effects measured for the oxidation of mandelic acid" by Pb(OAc)4 in benzene and in benzene-pyridine... 

If the reaction rates of a specific carbene with various quenchers are studied in the same solvent, and with small concentrations of Q, K will be constant. Relative reactivities for the singlet state of a spin-equilibrated carbene can thus be derived. However, few researchers have varied the acidity of ROH, estimated kinetic isotope effects, and compared alcohols with ethers (Table 4). The data indicate proton transfer to diarylcarbenes (139d, 139k, 205, 206)112-117 and diadamantylcarbene (207).118... 

The time-resolved, chemical behavior of FL depends on the solvent. Irradiation of DAF in cyclohexane gives FLH The lifetime of FL in cyclohexane is 1.4 ns, and the ratio of products obtained (26) indicates that both direct insertion and abstraction-recombination mechanisms are operating (Griller et al., 1984b). Replacement of the cyclohexane by its deuteriated counterpart reveals a kinetic isotope effect of ca 2 (Table 5). 

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