Intermolecular interaction forces,relative strengths

Table 1. Intermolecular interaction forces and their relative strengths (according to [8 ).

There has been much discussion of the relative contributions of the no-bond and dative structures to the strength of the CT complex. For most CT complexes, even those exhibiting intense CT absorption bands, the dative contribution to the complex stability appears to be minor, and the interaction forces are predominantly the noncovalent ones. However, the readily observed absorption effect is an indication of the CT phenomenon. It should be noted, however, that electronic absorption shifts are possible, even likely, consequences of intermolecular interaetions of any type, and their characterization as CT bands must be based on the nature of the spectrum and the structures of the interaetants. This subject is dealt with in books on CT complexes. ... 

The relative distribution of a solute between two phases is determined by the interactions of the solute species with each phase. The relative strengths of these interactions are determined by the variety and the strengths of the intermolecular and other forces that are present, or, in more general terms by the polarity of the sample and that of the mobile and stationary phases. 

Intermolecular forces will determine the behavior of all materials in every phase in which they exist. Intermolecular forces can be classified into (1) dispersion, (2) dipole, (3) induction, and (4) hydrogen bonding. The relative strength of these forces can be stated as dispersion < dipole < induction < hydrogen bonding. Owing to the low polarizability of the C—F bond, the dominant intermolecular force is often dispersive in character. The extension to more dominant forces should become obvious as more complicated molecules are discussed. The discussion here can be confined to simple pair-wise interactions between two molecules or polymer chains that contain C—F bonds. 

Sample Problem 3.1 illustrates how to determine the relative strength of intermolecular forces for a group of compormds. Table 3.4 summarizes the four types of interactions that affect the properties of all compounds. 

The activity coefficient at infinite dilution of a solute y°° is related to the relative strength of an intermolecular interaction with the ionic liquid. The choice of the model solutes was based on their Abbout-Kamlet-Taft parameters [4, 75, 76], to exhibit prevailing forces with regard to the hydrogen bond acceptor, donor and polarisability properties. Similar probe molecules have been used in computational studies [62, 63],... 

In a pure liquid all the intermolecular forces are between like molecules when the liquid and a solute are mixed, each molecule then interacts with molecules (or ions) unlike it as well as with like molecules. The relative strengths of these interactions help to determine the extent of solubility of a solute in a solvent. The main interactions that affect the dissolution of a solute in a solvent follow. 

Identify the intermolecular attractive interactions (dispersion, dipole-dipole, hydrogen bonding, ion-dipole) that exist between molecules or ions based on their composition and molecular structure and be able to compare the relative strengths of these intermolecular forces. (Section 11.2)... 

PVC is a nonflammable and durable polymer formed from a vinyl chloride monomer. The C-Cl functional group in PVC is relatively polar, and nonspecific dispersion forces dominate the intermolecular interactions [2]. Consequently, PVC has an amorphous structure with a small degree of crystallinity. PVC is used as the polymer backbone in membranes because of its strength, inertness, and compatibility with a variety of carriers and plasticizers. Unlike CTA, PVC is also resistant to acid solutions since it is not prone to acid hydrolysis. 

Methane is a gas at room temperature and atmospheric pressure. It can be converted to a liquid if cooled to - 164°C, and to a solid if further cooled to - 182°C. The fact that methane (or any other compound, for that matter) can exist as a Uquid or a solid depends upon intermolecular attraction. Although the forces of attraction are generally electrostatic, they vaiy widely in relative strength. The strongest attractive forces are between ions, as for example between Na and Cl" in NaCl [787 kj (188 kcal)/mol]. Dipole-dipole interactions and hydrogen bonding [8-42 kJ (2-10 kcal)/mol] are weaker. We shall have more to say about these intermolecular attractive forces in Chapter 10. 

In liquids and solids, molecules are held together by intermolecular attractions. These forces also play a central role in the formation of solutions. When one substance (the solute) dissolves in another (the solvent), particles of the solute disperse throughout the solvent. The solute particles occupy positions that are normally taken by solvent molecules. The ease with which a solute particle replaces a solvent molecule depends on the relative strengths of three types of interactions ... 

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