Brown constant

On the other hand, the rate constant k does not depend on the changing steric influence of substitutents in the 8-position, but correlates surprisingly well with the Hammett-Brown constant cr. This result indicates that the formation of an sp3-hybridized carbon atom (at the 1-position of the o-complex) leads to a compound without significant steric interaction of the electrophile with substituents in the 8-position. The o-complex cannot be planar and is asymmetric. The preferred conformation of a o-complex of this type is illustrated in Figure 12-6. The pseudoax-ial position of the electrophile E reduces the steric interaction between this group and the peri substituent R. 

The strong electron-withdravhng effect of the CeFs group that is estimated to have a Hammett constant ap of 0.4 [16,17] and a Brown constant of 0.99 [18,19]. The... 

The Souders and Brown constant CSB is the C-factor [Eq. (14-77)] at the entrainment flood point. Most modern entrainment flooding correlations retain the Souders and Brown equation (14-80) as the basis, but depart from the notion that CSB is a constant. Instead, they express CSb as a weak function of several variables, which differ from one correlation to another. Depending on the correlation, CSB and us,flood are based on either the net area or on the bubbling area AB. 

A good correlation between log Kr and the Hammett-Brown constant cr+ of substituent X was obtained in the series 3-11 (see Table II and references therein) ... 

Smoker method. 123-126, 192 Snap-Grid , 466-467, 637, 650 Souders and Brown constant. 276 equation, 276, 480 Spiegel and Meier flood. MeUapak , 488, 490 mass transfer. 474, 532 ST-100 packing, 444 Standart efficiencies, 365 Stichlmair et al. packing maldistribution, 547 packing pressure drop model, 501 Strigle ... 

Most benzylic solvolyses generating relatively stable carbocations belong to a category to which the Brown constants are effectively applicable. Extensive data on a,a-dialkylbenzyl solvolyses are available from Brown s original studies, and a wide set of benzylic substituent effects were included in Johnson s (1978) compilation of Brown correlations. Although all these... 

Most benzylic solvolyses generating relatively stable carbocations belong to a category to which the Brown constants are effectively applicable. Extensive... 

The logarithms of these values are correlated with the Hammett constant cand the Brown constant (with the parameters p = 3.0and = -1,5) The kinetic isotope effect of the reaction is small ( 3 for benzene and 2.3 for toluene). 

Figure VIII.3. The correiation between the logarithms of relative rate constants of the oxidation of substituted toluenes XC6H4CH3 and the Brown constants a of substituent X.

Vanadium complexes and in particular [VO(acac)2] are the most active catalysts for the oxidation of substituted anilines to nitro compounds. The effect of substituents upon reaction rate corresponds to a reaction involving an electron deficient transition state in that electron withdrawing groups decrease the rate and vice versa. The relative order of reactivity p-Me > m-Me > aniline > p-Cl > p-Br > m-Cl > m-Br is the same as observed in electrophilic aromatic substitution. Straight line correlations between the log of the relative rates and Hammett a or Brown constants were obtained with p values of— 1.42 and — 1.97, respectively, indicating an electron deficient transition state in the rate determining step. 

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