Diamagnetic susceptibility molar

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 molar diamagnetic susceptibility of thiazole and some derivatives was initially determined by the classical Curie-Cheneveau method (5,315,316) and later confirmed by a method (317) based on the difference of NMR proton chemical shift of a sample of tetramethylsilane immersed in the liquid to be investigated, according to the shape (cylindrical or spherical) of the sample tube (Table 1-47) (318),... 

Other physical methods were also applied to the elucidation of the isomerism of diazocyanides, e. g., determination of diamagnetic susceptibility, the Faraday effect (optical rotation in a magnetic field), and electronic and infrared spectra. Hantzsch and Schulze measured ultraviolet spectra at a remarkably early date (1895 a). Unfortunately, their results and later work (Le Fevre and Wilson, 1949 Freeman and Le Fevre, 1950) did not allow unambiguous conclusions, except perhaps the observation that the molar extinction coefficients of the band at lowest frequency are consistently larger in all types of (i -compounds Ar — N2 - X than in the corresponding (Z)-iso-mers (Zollinger, 1961, p. 62). 

Some diamagnetic crystals (graphite, bismuth, naphthalene and other aromatic substances) show prohounced diamagnetic anisotropy. The observed anisotropy of crystals of benzene derivatives correspond to the molar diamagnetic susceptibility —54 X 10 with the field direction perpendicular to the plane of the benzene ring and —37 X lO"6 with it in the plane. This molecular anisotropy has been found to be of some use in determining the orientation of the planes of aromatic molecules in crystals.1... 

Only the diamagnetic susceptibility and the second moment of the nuclear magnetic resonance show additive molar properties. 

TABLE 12.3 Group contributions to molar diamagnetic susceptibility -Xm (in 10 -12 3 m mol )... 

B. Correlation for the molar diamagnetic susceptibility References and notes for Chapter 10... 

Magnetic properties will be discussed, and a new correlation for the molar diamagnetic susceptibility will be presented, in Chapter 10. 

The magnetic susceptibility C, and the molar diamagnetic susceptibility m (see Equation 10.2) are nearly independent of the temperature. They are usually expressed in units of 1Q 6 cc/g and 10 6 cc/mole, respectively, and C,m is predicted by using group contributions. 

Table 10.1. The molar diamagnetic susceptibility calculated by group contributions, the correction index N s used in the correlation equation, and the fitted or predicted (fit/pre) values of m, for 125 polymers. For 15 of these polymers, cannot be calculated via group contributions, but can be calculated by using the new correlation. The values of °%v used in the correlation equation are all listed in Table 2.2. is expressed in units of IQ-6 cc/mole.

Figure 10.1. A correlation for the molar diamagnetic susceptibility C,m calculated by using group contributions for 110 polymers. C,m is expressed in 10"6 cc/mole.

For rare-gas atoms <0 a 0> can be evaluated from observed values of molar diamagnetic susceptibility by use of the relation... 

TABLE I. Polarizability a, Molar Diamagnetic Susceptibility and Derived Quantities. 

A (diamagnetic susceptibility exaltation parameter) = Am—Am, all in units of —10- cm3 mol-1. Am is the experimentally determined molar susceptibility, Am- is the susceptibility estimated for a model cyclopolyene (neglecting ring current corrections) 28>. 

The concept of the closely related diamagnetic susceptibility exaltation was earlier discussed by Craig88 and Dauben et al,83 These groups suggested that the difference, the exaltation, in the observed molar magnetic susceptibility xm and that calculated from atomic and bond contribution Xm, provides a useful criterion for assessing aromaticity. Dauben et al.84 have recently provided an authorative survey of the subject and a comprehensive compilation of exaltation values for benzenoid, nonbenzenoid, and pseudo-aromatics, aromatic cations, keto aromatics and heteroaromatics. Examples of the last series are provided here in Table VI. Some uncertainties arise in the calculations of xm- for five-membered heteroaromatics. 

Weak diamagnetic materials have magnetic susceptibility values close to zero their molar magnetic susceptibility is of the order of Xmoi = —10 x Kr9m3mol 1. Diamagnetic susceptibility is a temperature independent quantity (Fig. 7.1). Some diamagnetic materials (water, benzene) are used to calibrate (check) the experimental equipment. 

The diamagnetic molar susceptibility (Xm) also depends on ring current and can be measured relatively easily. The difference between this value and that obtained for a classical localized model affords the diamagnetic susceptibility exhaltation (A) . A comparison of the aromaticity indices of thiophene and benzene by magnetic criteria are displayed in Table 19. In all cases, the order of aromaticity as determined by these magnetic criteria follow the sequence benzene > thiophene > pyrrole > furan. 

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