Repulsion resulting from

Entries 11 and 13 in Table 3.4 present data relating the efiect of methyl substitution on methanol and methylamine. The data show an increased response to methyl substitution. While the propane barrier is 3.4 kcal/mol (compared to 2.88 in ethane), the dimethylamine barrier is 3.6kcal/mol (compared to 1.98 in methylamine) and in dimethyl ether it is 2.7 kcal/mol (compared to 1.07 in methanol). Thus, while methyl-hydrogen eclipsing raised the propane barrier by 0.5 kcal/mol, the increase for both dimethylamine and dimethyl ether is 1.6 kcal/mol. This increase in the barrier is attributed to greater van der Waals repulsions resulting from the shorter C—N and C—O bonds, relative to the C—C bond. 

X-ray diffraction patterns for different carbon/fluorine ratios demonstrate that the diffractions due to the starting materials disappear and are replaced by new diffractions.12 As shown in Table 2,12 the interlayer spacing of graphite and carbon black increases from 3.37 to 6.06 and 6.7 A. This increase is due to the electrostatic repulsion resulting from the fluorine atoms which have formed a layer above and below the carbon atoms. 

Growth cones are subject to both chemoattractant and chemorepellent effects of guidance molecules and also to attraction or repulsion resulting from cell cell-contacts. To complicate the picture further, the netrins and also the brain-derived neurotrophic factor BDNF (see Fig. 30-6D) may first attract, and then after a period of adaptation or desensitization, repel a growth cone.4 13 4 4 446 443 Consecutive phases of desensitization and resensitization may result in a zig zag path of... 

In conventional latices, the colloidal stability of the particles arises from the predominance of the electrostatic forces of repulsion over the London-van der Waal s forces of attraction. These electrostatic forces of repulsion result from the electric double layer formed by the emulsifier ions adsorbed on the hydrophobic polymer particle surface and the counterions from the aqueous phase. The London-van der Waal s forces of attraction are strongest when the particle-particle distance is very small. Therefore, in most particle-particle collisions, the particles repel one another until the particle-particle distance is decreased to the point where the London-van der Waal s forces of attraction are predominant over the electrostatic forces of repulsion. Thus, many conventional latices remain stable indefinitely without significant stratification or flocculation of the particles. 

To avoid this inconsistency, Jeffrey and Yates (238) suggested that the Kj term for 122 is underestimated as a result of underestimation of steric repulsions resulting from the use of a minimal STO-3G basis set. Consequently, would include some steric interactions which favor the ap conformation. 

In these polymers, apart from the electrostatic repulsion, resulting from like charges occurring on the surface of cement grains, the so-called steric hindrance is produced, due to the presence of side chains. This steric repulsion is very important as a dispersive interaction in cement water suspension (see Fig. 6.99). 

The first term on the left-hand side represents the kinetic energy of the electron, and the second term the potential energy, e. is the energy of the electron in the fth orbital. The potential energy term, F(r ), is calculated by assuming that the electrical repulsion resulting from all the other electrons can be represented by a static, spherically symmetric charge distribution. A difficulty with this procedure is that it is impossible to calculate V(r.) until the one-electron wavefunctions of all the other electrons are known. Thus, all the one-electron wavefunctions derived from equation (7.38) are interrelated, which makes the problem difficult to solve. 

The repulsion resulting from addition or removal of a second IS electron leads to a change in the electrostatic energy of the nanoparticle given by ... 

Steric strain in alkanes may also be due to van der Waals repulsion resulting from concentrated alkyl branching. Consider the structures in Figure 3.40, all of which have three f-butyl groups and one other alkyl group bonded to a central carbon. De SUva and Goodman studied these structures with molecular mechanics calculations and determined that 16,17, and 18 should be stable at room temperature. The possible existence of 19 was... 

The rotational barrier in methylsilane (Table 3.3, entry 5) is significantly smaller than that of ethane (1.7 versus 2.88 kcal/mol), probably because of decreased internuclear repulsions resulting from the longer silicon-carbon bond length of 1.87 A, compared to 1.54 A for ethane. 

When a neutral atom is converted to an ion, its size changes. If the atom forms an anion, its size (or radius) increases because the nuclear charge remains the same but the repulsion resulting from th dditional electron(s) enlarges the domain of the l wK)mS )inai3iQ(S,QlS he other hand, its size decreases... 

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