Parachor, atomic

Mumford and Phillips33 were the first to evaluate the influence of chain branching on the molecular parachor of hydrocarbons. They calculated values for the atomic parachors, which formed the basis for the specific parachor vs. molecular weight diagram of Leendertse and Waterman34 (Fig. 56). In this diagram curves are drawn... 

Fig. 56. Diagram for saturated non-branched hydrocarbons (based on values of the atomic parachor given by Mumford and Phillips) according to Leenderise and Waterman84...

The atomic parachors are an approximation to the volumes of the atoms in coordinate or covalent combination it will be seen that there is a rough correspondence between the atomic parachors and the atomic volumes in Lothar Meyer s curve. 

The parachors of phosphorus and the other atoms were summed and compared also with the molar values of POCl3, etc. (p. 54). A different series of atomic parachors has also been proposed.8... 

This is primarily an additive property, the parachor of a compound being the sum of the atomic parachors, with some additional terms where certain structures, such as double and triple bonds and cyclic structures, are present. Since Qg is usually small compared with it m y be neglected and the parachor taken as ... 

A linear relation of the atomic parachor of an element to that of the corresponding inert gas has been claimed, It is possible to express the parachor without explicit reference to the surface tension by means of the formula ... 

Values for the steric parameter V/lOO were calculated from atomic parachors, through a characteristic molecular volume (Vx) to a corresponding intrinsic molecular volume (Vj). 

Laubengayer, A.W., Ferguson, R.P., Newkirk, A.E., 1941. The densities, surface tensions and parachors of diborane, boron triethyl and boron tribromide. The atomic parachor of boron. J. Am. Chem. Soc. 63, 559-561. 

Similarly, the atomic parachor of a carbon atom is calculated as follows. 

However, there are other molecular properties, such as molar volume, molar refi action [3], diamagnetic susceptibility [4], and parachor [5], that can be obtained to sufficient accuracy fi om contributions, p , of its N atoms (Eq. (5)). 

The temperature-independent parachor [P] may be calculated by the additive scheme proposed by Quale.The atomic group contributions for this method, with contributions for silicon, boron, and aluminum from Myers,are shown in Table 2-402. At low pressures, where Pi. pc, the vapor density term may be neglected. Errors using Eq. (2-168) are normally less than 5 to 10 percent. 

TABLE 2-402 Atomic Group Contributions for Calculation of the Parachor [P]... 

Estimation of a with 5.3.1 requires solely the input of pi and parachor. Parachor can be derived from molecular structure with schemes based on group additivity. Exner [4] gives an excellent review and discussion of various group contribution methods for parachor. A very simple method has been developed by McGowan [5] employing only atomic contribution and the number of bonds, A bonds ... 

Quinones et al. (2000) reported the successful use of neural networks to predict the half-life of a series of 30 antihistamines. The input for the network was derived from the output of CODES, a routine that generates descriptors for a structure based on atom nature, bonding, and connectivity. Attempts to correlate the half-life with the physicochemical parameters log Kow, pKa, molecular weight, molar refractivity, molar volume, parachor, and polarity were unsuccessful. In a subsequent study by Quinones-Torrelo et al. (2001), the authors correlated the half-life of 18 antihistamines with their retention in a biopartitioning micellar chromatography system with a resultant correlation coefficient (R2adj) value of 0.89. The correlation is explained in that the retention in this system is dependent on hydrophobic, electronic, and steric properties, which are also important in determining half-life. 

The values of several atomic and constitutive parachors are as follows ... 

Some quite small deviations between the observed parachors of compounds and those calculated from the sum of the atomic and constitutive parachors have been pointed out by Hunten and Maass,1 and by Mumford... 

The parachor was introduced by Sugden (1924), who gave a list of atomic constants. Later the atomic and group contributions were slightly modified and improved by Mumford and Phillips (1929) and by Quayle (1953). 

Arylates, 140 Aspect ratio, 844 Atomic contributions, 61 Atomic and structural contributions to the parachor, 231... 

Equation 10 generalizes the expression of Erdos (31) applicable to components involving the same functional group. Returning to the constant C in Equation 10, usually the number of carbon atoms does not directly affect the constant. Apparently this effect is corrected by the parachor which changes with the number of carbon atoms. For example, for aromatics in furfural ... 

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