Magnetic bond numbers

Figure 1. The dependence of the magnetic bond number Nb on z = wj fL calculated from equation (9) of reference (Rosensweig et aL, 1983) (dashed line) and from equation (2) (solid line). The results are shown for a magnetic susceptibility x of 1.6. The phase ratio is fixed at 0.5.

Nuclear magnetic resonance spectra show that the compound exists as a monomer in the molten state IR and Raman data show that the same molecular structure exists for the solid state Sawodny and Goubeau calculated the force constants from the normal vibrations of the molecule, after they had corrected the original assignments of the bands A bond number of 0.78 was found for the P—B bond. The chemical shifts and coupling constants from the H and B n.m.r. spectra for molten BH3PH3 are given in Table 9... 

Monomer (Section 6 21) The simplest stable molecule from which a particular polymer may be prepared Monosaccharide (Section 25 1) A carbohydrate that cannot be hydrolyzed further to yield a simpler carbohydrate Monosubstituted alkene (Section 5 6) An alkene of the type RCH=CH2 in which there is only one carbon directly bonded to the carbons of the double bond Multiplicity (Section 13 7) The number of peaks into which a signal IS split in nuclear magnetic resonance spectroscopy Signals are described as singlets doublets triplets and so on according to the number of peaks into which they are split... 

Only a limited number of coal-denved pitches were examined by H NMR because of their low solubility in solvents commonly used m conventional proton magnetic resonance. Table 12 reports the distribution of hydrogen for three of the pitches. Unlike coal-tar pitches, which typically have over 85% of the hydrogen bonded to aromatic carbon, the matenals listed in Table 12 are characterized by a high content of aliphatic hydrogen. 

A major weakness of valence bond theory has been its inability to predict the magnetic properties of molecules. We mentioned this problem in Chapter 7 with regard to the 02 molecule, which is paramagnetic, even though it has an even number (12) of valence electrons. The octet rule, or valence bond theory, would predict that all the electrons in 02 should be paired, which would make it diamagnetic. 

It is then shown that (excepting the rare-earth ions) the magnetic moment of a non-linear molecule or complex ion is determined by the number of unpaired electrons, being equal to ms = 2 /S(S + 1), in which 5 is half that number. This makes it possible to determine from magnetic data which eigenfunctions are involved in bond formation, and so to decide between electron-pair bonds and ionic or ion-dipole bonds for various complexes. It is found that the transition-group elements almost without exception form electron-pair bonds with CN, ionic bonds with F, and ion-dipole bonds with H2O with other groups the bond type varies. 

The multiplicity can be determined from the experimental values of the magnetic susceptibility, the magnetic moment in Bohr magnetons being equal to 2 VS(S + l), in which S is the spin quantum number. (The multiplicity is 2S + 1.) The moments for 22 and 62 are 1.73 and 5.91, respectively. The experimental values for K3Fe(CN)6 and (NH jFeF are 2.0 and 5.88, respectively, so that the bonds in the [FefCN ] ion are electron-pair bonds, and those in [FeFe]a are ionic. 

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