Hydrogen bonding factor

This postulate assumes that steric, hydrophobic, electronic, and hydrogen bonding factors that affect partitioning in the biophase are handled by the octanol/water system. Given that the biological response (log I/O is proportional to logPbio then it follows that... 

Consequently, the hydrogen-bonding factor in the partition function becomes... 

Like the amides (see below), the pyrrole and indole bases deviate badly from the activity coefficient behavior of the Hammett indicators (185,357). This is perhaps not too surprisii since they protonate on carbon to produce a delocalized carboniunr-ammonium ion. As a result, the pyrrol seem to require their own separate acidity function intermediate between those for Hammett bases and aiylolefins. It is significant that both the a- and protonated conjugate acids appear to follow this acidity scale over a wide range (357). This is further evidence that the acidity fimctions differ more as a result of hydrogen-bonding factors than variations in delocalization (82,85). 

The extensive researches of Gerrard and his co-workers on the solubility of HCl in various solvents include a number of alcohols (121,123-127,129,130). The meanii of this combined measurement of basicity and hydrogen bonding factors is probably made even more obscure for the alcohols than for other solvents since the hy-droxylic solvents can serve not only as hydrogen bond acceptors from the protonic end of the HCl dipole but can also donate a hydrogen bond to stabilize anions or the anionic ends of dipoles (348). It is found that these results for the alcohols form an orderly picture that is readily interpretable in terms of inductive and steric factors. 

A microwave pulse from a tunable oscillator is injected into the cavity by an anteima, and creates a coherent superposition of rotational states. In the absence of collisions, this superposition emits a free-mduction decay signal, which is detected with an anteima-coupled microwave mixer similar to those used in molecular astrophysics. The data are collected in the time domain and Fourier transfomied to yield the spectrum whose bandwidth is detemimed by the quality factor of the cavity. Hence, such instruments are called Fourier transfomi microwave (FTMW) spectrometers (or Flygare-Balle spectrometers, after the inventors). FTMW instruments are extraordinarily sensitive, and can be used to examine a wide range of stable molecules as well as highly transient or reactive species such as hydrogen-bonded or refractory clusters [29, 30]. 

AG and AH can be expressed as a multiplicative function of hydrogen bonding in different polar and nonpolar solvents by means of enthalpy acceptor factors E - enthalpy donor factors free energy acceptor factors Q, and free energy donor factors Q (Eqs. (32) and (33), where kj, 2- 3 [kcal/mol] are regression coefficients). 

The solubility of a compound is thus affected by many factors the state of the solute, the relative aromatic and aliphatic degree of the molecules, the size and shape of the molecules, the polarity of the molecule, steric effects, and the ability of some groups to participate in hydrogen bonding. In order to predict solubility accurately, all these factors correlated with solubility should be represented numerically by descriptors derived from the structure of the molecule or from experimental observations. 

Other factors that can stabili2e such a forming complex are hydrophobic bonding by a variety of mechanisms (Van der Waals, Debye, ion-dipole, charge-transfer, etc). Such forces complement the stronger hydrogen-bonding and electrostatic interactions. 

The reaction rate of molecular oxygen with alkyl radicals to form peroxy radicals (eq. 5) is much higher than the reaction rate of peroxy radicals with a hydrogen atom of the substrate (eq. 6). The rate of the latter depends on the dissociation energies (Table 1) and the steric accessibiUty of the various carbon—hydrogen bonds it is an important factor in determining oxidative stabiUty. 

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