Parachor, molecular

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... 

Thus the parachor is the molar volume compensated for variations in intermolecular attraction by multiplying by the fourth root of the surface tension. Molecular parachors can be calculated by summation of parachor equivalents. Classical values [3 1 of these are given in Table 5.1. Application to chloroform, for example, gives. 

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)). 

Values for hydrocarbons other than alkynes and alkadienes can be predicted by the method of Suzuki et al. The best model includes the descriptors T, P, the parachor, the molecular surface area (which can be approximated by the van der Waals area), and the zero-order connectivity index. Excluding alkynes and alkadienes, a studv for 58 alkanes, aromatics, and cycloalkanes showed an average deviation from experimental values of about 30 K. 

G = superficial mass vapor velocity based on the cross-sectional area of the column, Ib/hr-sq ft M = molecular weight, Ib/lb mole N = dimensionless number P = pressure, consistent units [P] = Sugden parachor sg = specific gravity T = temperature, °F U = superficial velocity, ft/hr... 

A small number of physical properties appears to provide more definite information these are molecular refraction, parachor, and (in a more limited way) ultraviolet absorption6. 

On the basis of these values one can conclude that, with increasing bond orders, the force constants rise, suggesting that the S—O bond of sulphoxides should have more semipolar character than that of sulphones. Furthermore, molecular diffraction measurements and Parachors for sulphoxides also suggest that the S—O bond in sulphoxides should have a semipolar single-bond representation while the S—O bond in sulphones is described by double bonds or better as the resonance hybride shown in Scheme 1. 

Over the past twenty years many volume or "bulk" parameters have been proposed, Including Van der Waals (Vw) Traube (Vt) molar (Vm) and molal (V ) volumes parachor (Pch), group molar refraotlvlty (MR) and molecular weight (li ) (2). The use of surface areas such as the Van der Waals area (A ) as parameters has also been proposed. As we remarked previously there has been much disagreement as to the Interpretation of correlations with these parameters. 

Constitution XV for sucrose has up to the present satisfied all demands made upon it. Like its precursors, I and II (page 6), it was not incompatible with physical properties of sucrose such as the magnetic rotation, or the parachor, although the latter claim has been denied. Von Lippmann lists a great many early determinations of the physical properties of the sugar more recent measurements include the heat of combustion, the molecular weight in liquid ammonia, and various optical and electrical constants. ... 

Sugden J.G.S. cxxv. 1177, 1924 cxxvii. 1525, 1868, 1925) has compared the molecular volumes of substances under conditions such that they possess identical surface tensions and has shown that they are determined by the molecular constitutions of the substances. In obtaining the parachor P Sugden makes use of the approximate relationship between free surface energy and density noted by Macleod Trans. Farad. Soc. xix. 38, 1923) a = c(pi- p y... 

Recently, Tichy investigated 41) the dependencies of the steric constants, Es, v, L, Bj, B4, MV (molar volume), [P] (parachor), MR (molar refraction), MW (molecular weight), and % (molecular connectivity index) on lipophilicity, as it is measured by n 42) and f43) constants. The data were treated by factor analysis methods. 

The results of calculations as illustrated in Example 11-21 should be within 10 percent of laboratory measured values. Better accuracy will be obtained if the heptanes plus fraction is divided into several fractions and the parachor for each fraction obtained from Figure 11-18 according to the molecular weight of the fraction. This is the manner in which the data of Figure 11-18 were obtained. The deviation of the heavier fractions from the line on Figure 11-18 is attributed to the collection of asphaltenes in the heaviest fraction of the liquid.15 The correlation line obviously does not give good values of parachors for this fraction. 

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. 

Hydrogen bonds were first detected through solubility studies (1497), and were quickly found by the many other classical methods available in the first quarter of the twentieth century. Vapor pressure and vapor density, molecular weight, dielectric constant, partition or distribution, molar volume, parachor, refractive index, electrical and thermal conductivity, and acoustic behavior are a few of the physical properties that reflect the presence of the H bond. 

Parachor. The parachor is the best known of a group of additive functions related to molecular volume and based usually on some easily measurable quantities. Parachor is almost the only one of these which has been applied to H bonding, but similar findings would probably hold for others. There is some question about the theoretical basis for the parachor (1707), and perhaps it should be considered an essentially empirical relation. 

Sidgwick and Bayliss (1875) studied o-substituted phenols and noted that the experimental parachor is lower than that calculated from the atomic values. They assigned this lowering to the formation of a chelate ring, and derived a parachor value for this structural arrangement. With changing temperature, internally H bonded compounds reveal no change in parachor, in contrast to the increase usually found for inter-molecularly associated isomers (315). 

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