Force dipol

Until surface contact, the force between molecules is always one of attraction, although this attraction has different origins in different systems. London forces, dipole-dipole attractions, acid-base interactions, and hydrogen bonds are some of the types of attraction we have in mind. In the foregoing list, London forces are universal and also the weakest of the attractions listed. The interactions increase in strength and also in specificity in the order listed. 

The elution of compounds on GC columns is a complex process related to the volatility of the compound, which results from its boiling point, and the chemical interactions between the compound and the stationary phase. These interactions are typically those which arise from polar-polar interactions, dispersion forces, dipole-dipole interactions, and so forth. Collectively, they are described by the term the chemical potential, Ap.°, which derives from the potential for the compound to... 

Ihe boiling points of different molecular substances are directly related to the strength of the intermolecular forces involved. The stronger the intermolecular forces, the higher the boiling point of the substance. In the remainder of this section, we examine the nature of the three different types of intermolecular forces dispersion forces, dipole forces, and hydrogen bonds. 

We have now discussed three types of intermolecular forces dispersion forces, dipole forces, and hydrogen bonds. You should bear in mind that all these forces are relatively weak compared with ordinary covalent bonds. Consider, for example, the situation in HzO. The total intermolecular attractive energy in ice is about 50 kj/mol. In contrast, to dissociate one mole of water vapor into atoms requires the absorption of928 kj of energy, that is, 2(OH bond energy). This explains why it is a lot easier to boil water than to decompose it into the elements. Even at a temperature of 1000°C and 1 atm, only about one H20 molecule in a billion decomposes to hydrogen and oxygen atoms. 

Which of the following would you expect to show dispersion forces Dipole forces ... 

Force The product of mass times acceleration. See also Attractive forces Repulsive forces dipole, 237-238 dispersion, 236,104,107 intermolecular, 227-228,235-236 Formal charge The charge that an atom would have if the bonding electrons in a molecule were equally shared, 171-172,192-193q... 

Dispersion forces, dipole Interactions, and hydrogen bonds all are significantly weaker than covalent Intramolecular bonds. For example, the average C—C bond energy Is 345 kJ/mol, whereas dispersion forces are just 0.1 to 5 kJ/mol for small alkanes such as propane. Dipolar Interactions between polar molecules such as ace-tone range between 5 and 20 kJ/mol, and hydrogen bonds range between 5 and 50 kJ/mol. 

At the opposite extreme, molecular solids contain individual molecules bound together by various combinations of dispersion forces, dipole forces, and hydrogen bonds. Conforming to like dissolves like, molecular solids dissolve readily in solvents with similar types of intermolecular forces. Nonpolar I2, for instance, is soluble in nonpolar liquids such as carbon tetrachloride (CCI4). Many organic compounds are molecular solids that dissolve in organic liquids such as cyclohexane and acetone. 

B. hydrogen bonds, dispersion forces, dipole attractions... 

Molecular solids have their lattices composed of molecules held in place by London forces, dipole-dipole forces, and hydrogen bonding. Solid methane and water are example of molecular solids. 

Explanation Water is a polar substance with strong intermolecular hydrogen bonds. Dimethyl ether is a polar material with weaker intermolecular forces (dipole-dipole). It will... 

There are a number of different enthalpic interactions that can occur between polymer and packing, and in many cases multiple interactions can exist depending on the chemical structure of the polymer. Enthalpic interactions that are related to water-soluble polymers include ion exchange, ion inclusion, ion exclusion, hydrophobic interactions, and hydrogen bonding (12)- Other types of interactions commonly encountered in SEC, as well as in all other chromatographic separations, are dispersion (London) forces, dipole interactions (Keeson and Debye forces), and electron-donor-acceptor interactions (20). 

Molecular Dispersion forces, dipole-dipole forces, hydrogen bonds Soft, low-melting, nonconducting H20, Bt2, co2, ch4... 

For molecular solids, the structural units are atoms or molecules. They are bonded by hydrogen bonds or dipole-dipole dispersion forces. Dipole-dipole... 

A substrate binds an enzyme at the active site. Substrate-enzyme binding is based on weak intermolecular attractions contact forces, dipole forces, and hydrogen bonding. Steric effects also play an important role because the substrate must physically fit into the active site. Some enzymes have confined active sites, while others are open and accessible. A restricted active site can lead to high selectivity for a specific substrate. Low specificity can be advantageous for some enzymes, particularly metabolic and digestive enzymes that need to process a broad range of compounds with a variety of structures. Because enzymes are composed of chiral amino acids, enzymes interact differently with stereoisomers, whether diastereomers or enantiomers. 

There also exist dispersion, or London-van der Waals forces that molecules exert towards each other. These forces are usually attractive in nature and result from the orientation of dipoles, and may be dipole-dipole (Keesom dispersion forces), dipole-induced dipole (Debye dispersion forces), or induced dipole-induced dipole... 

For a solute to dissolve in a solvent, the cohesive forces that hold the solute molecules together (e.g., London forces, dipole-dipole interactions) should be the same as those that hold the solvent molecules together. 

Release of high-energy water Release of conformational strain Van der Waals forces Hydrogen bonding London dispersion forces Dipole-dipole interaction... 

The solubilities of the solutes in an aqueous system determined from Equation (3.20) are usually larger than experimental values, as shown in Figure 3.2. This normally occurs for solutes (especially crystalline solids) in polar solvents. There are many interactions between the solute and the polar solvent self-association of the solute or the solvent, solvation of the solute by the polar solvent, complexation in solution, etc. A modification of Equation (3.20), known as the extended Hildebrand solubility approach, has been developed. In this approach, it is assumed that the activity coefficient is partitioned into two forces van der Waals forces and residual forces (dipole-dipole and hydrogen-bonding forces). 

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