Polarity and bond strength

The reactions of germanium and tin compounds with HFA are very similar to those of silicon compounds. But because of differences in polarity and bond strengths some reactions yield products different from those of their silicon analogues. 

The Combined Effect of Bond Polarity and Bond Strength We can see the combined effect of bond polarity and bond strength by examining the trends in acidity of the gronp 6A and 7A hydrides as shown in Figure 15.14 . The hydrides become more acidic from left to right as the H—Y bond becomes more polar. The hydrides also become more acidic from top to bottom as the H—Y bond becomes weaker. 

The data of Table 1.2 and Table 1.3 clearly cannot be rationalized purely in terms of the relative stabilities of the product radicals. Rather, a complex interplay of polar, steric, and bond strength terms5 must be invoked.13 In the following sections, each of these factors will be examined separately to illustrate their role in determining the outcome of radical addition. 

For mono- and 1,1-disubstituted monomers, steric, polar, resonance, and bond-strength terms (see Section 2.3) usually combine to favor a preponderance of tail addition Le. an almost completely isoregic structure. Fiowever, the occurrence of... 

What Do We Need to Know Already This chapter huilds on the introduction to acids and bases in Section J. It also draws on and illustrates the principles of thermodynamics (Chapters 6 and 7) and chemical equilibrium (Chapter 9). To a smaller extent, it uses the concepts of hydrogen bonding (Section 5.5), bond polarity (Section 2.12), and bond strength (Sections 2.14 and 2.15). 

Mo2(02CCH2).. Metal compounds with multiple metal-metal bonds such as Mo2(02CCH3)4 of symmetry, have attracted much experimental and theoretical attention focussed on the description of bonding and bond strength (46-48). Their electronic structure has been investigated experimentally by various methods such as resonance Raman, photoelectron spectroscopy, ultraviolet absorption and polarization studies of the matrix isolated sample (49-56). 

There has been considerable effort directed towards obtaining a fundamental understanding of the factors that govern the reactivities of carbon-centered radicals in bimolecular reactions, particularly with respect to their addition to alkenes [84]. From early liquid and gas phase studies, reactivity in such addition reactions was concluded to derive from a complex interplay of polar, steric, and bond-strength terms [85], which is much influenced by the nature and position of substituents on both the radical and the alkene. 

Carbon Dioxide, the highest oxidation product of carbon, is a stable (AG° = -394 kJ/mol), linear, non-polar molecule with C-0 bond length of 1.16A° and bond strength D = 532 kJ/mol. Even though it is a nonpolar molecule, CO2 contains polar bonds due to the electronegativity difference... 

Chromic acid removes amorphous regions of the polymer morphology, leading to the formation of complex (labyrinthine) cavities on the plastic surface. Some surface oxidation takes place. Improved wettability and bond strength have been ascribed to the topography of etched plastic surfaces rather than the polarity of the surface. ... 

Bond Polarity, Bond Moments, and Bond Strength... 

The cured polymers are hard, clear, and glassy thermoplastic resins with high tensile strengths. The polymers, because of their highly polar stmcture, exhibit excellent adhesion to a wide variety of substrate combinations. They tend to be somewhat britde and have only low to moderate impact and peel strengths. The addition of fillers such as poly (methyl methacrylate) (PMMA) reduces the brittleness somewhat. Newer formulations are now available that contain dissolved elastomeric materials of various types. These mbber-modifted products have been found to offer adhesive bonds of considerably improved toughness (3,4). 

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