Electron constants

The electronic constants for the 3-methylfuroxanyl and 4-methylfuroxanyl moieties (3 and 4) have been measured both appear to be strong electron-attracting groups... 

To reiterate, the amount of charge consumed during charging the double-layer is a function of potential, so as soon as coulometry commences, the charge held within the double-layer will change as ions adsorb and/or desorb in response to the change in potential. For convenience, we will discuss these processes in terms of a reduction reaction, with electrons constantly leaving the electrode. 

Table 1.13 Hammet s electronic constants of fluorinated substituents ...

One can see from eq. 32, that the problem of the evaluation of the energy distribution of the fragments also reduces (eq. 29) to the calculation of FC factors. Contrary to direct photodissociation, one now has several electronic constants. 

Final ionic Double-ionization State of electron- Constant of proportionality... 

Hammett substitution constants suffer from the disadvantage that they only apply to substituents directly attached to a benzene ring. Consequently, a number of other electronic constants (Table 4.5) have been introduced and used in QSAR studies in a similar manner to the Hammett constants. However, attempts to relate biological activity exclusively to the values of Hammett substitution and similar constants have been largely unsuccessful, since electron distribution is not the only factor involved (see section 4.4). 

The values for the large-scale constants are taken from the well-known tabulation of Birge, Phys. Rev. Supplement, Vol. 1, 1929. The atomic and electronic constants are taken or computed from the more recent values tabulated by Dunnington, Bull. Am. Phys. Soc., 14 (1), 17 (1939). 

Analogues of verapamil (1) were also studied for their calciiun channel antagonist activity, and their potency for isotonic contractile response of cat capillary muscle preparation was reported [30], which was foimd to be correlated with the electronic constant and the molecular volume of the B-ring substituents as ... 

Px and Ph represent the partition coefficients of a derivative and the parent molecule, respectively. Fujita and Hansch then combined these hydrophobic constants with Hammett s electronic constants to yield the linear Hansch equation and its many extended forms (19). 

Substituent electronic constants used to derive simple QSRR for real retention prediction potency have seldom succeeded. A wider application in that respect found the Hansch substituent hydrophobic constants, n 8], and Dross et al. [64] or Hansch and Leo [65] fragmental hydrophobic constants, /. The sums of these constants (plus corrections due to intramolecular interactions) account for the retention in reversed-phase liquid chromatographic systems [7,12). 

The tabulated molecular and electronic constants are taken from Barrow et al. (4). The state designations are those used by Barrow et al. who interpret the spectra in terms of type c coupling, when the state designations Z, n, etc. no longer have... 

Charton inductive constants - electronic substituent constants (O inductive electronic constants)... 

Derived from the Hammett equation, a electronic constants are calculated for different molecular substituents from the rate or equilibrium constant of specific reactions, with respect to a reference compound [Topsom, 1976 Charton, 1981 Taft and Top-som, 1987 Topsom, 1987b]. 

The Taft o constant (or o electronic constant, Taft polar constant) was proposed by Taft [Taft, 1956] to measure the inductive effect in the aliphatic series ... 

The factor 2.48 corresponds to the average of the available g values of alkaline hydrolysis from the Hammett equation and attempts to place o on the same scale as the Om and Op electronic constants. Since base-catalyzed hydrolysis involves both... 

Dual electronic constants o and o" were proposed to measure the exaltation of the resonance effect which appears when the substituent and active site bonded to a skeletal group give origin to a direct conjugation between them. 

According to the Swain-Lupton approach (SL), the a electronic constant is defined as a linear combination of the two basic electronic contributions [Swain and Lupton Jr., 1968 Swain et al., 1983 Swain, 1984 Reynolds and Topsom, 1984] based on the equation ... 

Swain and Lupton defined the field constant JF assuming that the polar effect was a component in both Hammett electronic constants On, and Opt... 

Figure E-2. Geometrical scheme for the calculation of the Dewar-Grisdale electronic constants.

Other substituent electronic constants were defined for specific different reference compounds (e.g. heterocycles) and reactions. 

Aryl electronic constants o are electronic constants defined for substituents on an aromatic ring different from benzene, such as pyridine [Otsuji et al, I960]. The concept may be generalized to various isocyclic and heterocyclic rings such as thiophene, furan, etc., and various types of aryl electronic constants o, oj", o may be also defined. A particular set of this kind is given by o electronic constants obtained by the protonation reaction of hydrocarbons, assuming as the reference compound a-naphthyl (a,. = 0). 

Phosphorus electronic constants or are electronic substituent constants derived from the dissociation constants of dialkylphosphinic acids for substituent groups directly bonded to a phosphorus atom [Mastryukova and Kabachnik, 1971]. Assuming the alkyl groups exert only an inductive effect, these electronic constants can be distinguished as Oy inductive constant and o resonance constant [Charton and Charton, 1978]. 

Radical electronic constants are substituent constants derived from free-radical reactions. The most popular are the radical parameter defined on the basis of the radical abstraction of a-hydrogens of substituted cumenes [Yamamoto and Otsu, 1967] and the ffa radical substituent constants defined by the benzylic a-hydrogen hyperfine coupling constants [Wayner and Arnold, 1984]. 

The electron donoivacceptor substituent constant k is an electronic constant proposed to measure the ability of a group to modify the stability of an electron donor-acceptor complex which is often referred to as charge transfer complex [Foster et al, 1978 Livingstone et al, 1979]. It is defined as ... 

Oj electronic constants of Dewar-Grisdale (36 - 39) represent o values determined from y-XCioHsCOOH substituted compounds (1-naphthoic acids) with j = 3, 4, 5, 6, 7 the corresponding percentages of resonance ( > %) are 29,57,38,43,48. 

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