And Hammett correlation

The role of substituents X on the mononuclear heterocyclic rearrangement (MHR) of 20 phenylhydrazones 54 of 3-benzoyl-5-phenyl-l,2,4-oxadiazole into the triazoles 55 (Equation 2) has been investigated, allowing the influence of X on the product distribution to be evaluated and first-order rate constants and Hammett correlations to be determined <1999T12885>. 

The absolute and relative rates of decomposition of tcrt-butyl phenylperacetates were measured in CDCI3 at 60, 70, 80, 90, 100 and 110°C and Hammett correlations were obtained (Table 3). An Eyring plot gave the activation parameters (Table 4). 

TABLE 3. Relative rates and Hammett correlations for the thermal decompositions of tcrt-butyl phenylperacetates in CDCI3... 

TABLE 7. Absolute rates, relative rates and Hammett correlations for ETR between tert-butyl perbenzoates and dimethyl sulfide... 

Oxidation of Cu with O2 is markedly slower than the analogous oxidation by TEMPO. The existence of a copper-centered dehydrogenation step was supported by investigating kinetic isotope effects and Hammett correlation studies using different substituted benzyhc alcohols. The /1-hydrogen abstraction was postulated to occur in a concerted mechanism with an -coordinated TEMPO radical bgand (Scheme 4). As such, this TEMPO-mediated copper-catalyzed oxidation of alcohols bears resemblance... 

In the [3 + 2] vs [2 + 2] controversy for the osmylation reaction,69,70 the pendulum has now swung in favour of the [3 + 2] mechanism. The main arguments are derived from kinetics and Hammett correlation, kinetic isotope effect (KIE),69,70 and quantum... 

These observations, along with kinetic isotope effect studies and Hammett correlation studies, support a concerted elimination by a-bond metathesis involving a four-membered transition state (Eq. 2) [23]. A large kinetic isotope effect is observed for the loss of methane from methyl amide complexes lb and lh (Eqs. 3 and 4), comparable to those observed by Buchwald and coworkers for formation of zirconium rj2-thioaldehyde complexes [25] and by Bercaw and coworkers for formation of tantalum rf- imine complexes [5a] through similar transition states. 

The importance of both electronic and steric factors is borne out by the reactions of piperidine in equation (159) at 30 °C in benzene (k, m" s" ) PhCOC=CPh (4-4), PhCOC=CBu-rt (1-9), PhCOC=CBu-/ (0 012), MeCOC=CPh (M5)i . If the steric requirements are made constant, as in a series of anilines in process (159) in 95% ethanol, the resulting rate data yield a satisfactory Bronsted plot and Hammett correlations /3 0-93 and p = —(212 to 2-18) in the range 20-50 °C . Further structure-reactivity variations were made with morpholine as nucleophile and XC6H4CSCCOC6H4Y as electrophile in 95% ethanol, the Hammett p = 1-13 to 0-97 for the X series and F42 to 1-20 for the Y series from 20-50 in r-BuOH at... 

O. Rogne, The Kinetics and Mechanism of the Reactions of Aromatic Sulphonyl Chlorides with Anilines in Methanol Bronsted and Hammett Correlations, J. Chem. Soc. B, 1971, 1855. 

PhI(OTf)2 is an effective oxidant for the direct formation of bicyclic diazenium salts from a variety of linear hydrazone precursors. This oxidative cyclization is postulated to occur by the iodine(III)-mediated formation of an l-aza-2-azoniaallene salt intermediate. A direct intermolecular allylic amination has been achieved with up to 99% yields using metal-free conditions. The reaction employs a hypervalent iodine(lll) reagent as an oxidant and bistosylimide as a nitrogen source. Mechanistic studies including isotope labelling and Hammett correlation indicated that depending... 

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