Inclusion intermolecular

Bulky, even if highly polari2able, functional groups or atoms that are attached anywhere but on the end of a rod-shaped molecule usually are less favorable for Hquid crystal formation. Enhanced intermolecular attractions are more than countered as the molecule deviates from the required linearity. For example, the inclusion of the bromine atom at position three of 4-decyloxy-3-bromoben2oic acid [5519-23-3] (9) prevents mesomorphic behavior. In other cases the Hquid crystal phases do not disappear, but their ranges are narrower. 

Several intermolecular interactions have been proposed and discussed as being responsible for the formation of cyclodextrin inclusion complexes in an aqueous solution 6-10). They are... 

A common feature of all clathrates discussed so far is a host lattice, by itself thermodynamically unstable, which is stabilized by inclusion of the second component. The forces binding this component must be similar in nature to the intermolecular forces in liquids. It seems natural, therefore, to regard a clathrate compound as a solid solution of the second component in the (meta-stable) host lattice. 

The process proceeds through the reaction of pairs of functional groups which combine to yield the urethane interunit linkage. From the standpoint of both the mechanism and the structure type produced, inclusion of this example with the condensation class clearly is desirable. Later in this chapter other examples will be cited of polymers formed by processes which must be regarded as addition polymerizations, but which possess within the polymer chain recurrent functional groups susceptible to hydrolysis. This situation arises most frequently where a cyclic compound consisting of one or more structural units may be converted to a polymer which is nominally identical with one obtained by intermolecular condensation of a bifunctional monomer e.g., lactide may be converted to a linear polymer... 

The solution phase is modeled explicitly by the sequential addition of solution molecules in order to completely fill the vacuum region that separates repeated metal slabs (Fig. 4.2a) up to the known density of the solution. The inclusion of explicit solvent molecules allow us to directly follow the influence of specific intermolecular interactions (e.g., hydrogen bonding in aqueous systems or electron polarization of the metal surface) that influence the binding energies of different intermediates and the reaction energies and activation barriers for specific elementary steps. 

Such weaknesses of the present implementation include the lack of an explicit inclusion of intermolecular forces other than excluded volume, resulting in a qualitatively inaccurate description of the equation of state. Another weakness is that the model shows lattice artefacts when dealing with problems of polymer crystallization or liquid-cristalline order only rather flexible poly-... 

At one extreme of the inclusion compounds variety are complexes, usually classified as solvates, in which molecules of the solvent are enclosed within intermolecular voids of the crystal to fill empty space or to complete a coordination sphere around a functional moiety. Quite often, it is difficult to control such a co-crystallization... 

When guest molecules are arranged together in the channel of a host-guest inclusion complex, intermolecular reactions of the guest compound may proceed stereoselec-tively and efficiently. An enantioselective reaction is expected when optically active host compounds are used. 

An additional example of a cycloamylose-induced rate acceleration which may be reasonably attributed to a conformational effect is the facilitation of the transfer of the trimethylacetyl group from the phenolic oxygen of 9 to the aliphatic oxygen of the adjacent hydroxymethyl group to form 10. This intramolecular transesterification is remarkably enhanced relative to a comparable intermolecular reaction,6 and occurs, at pH 7.0 and 25.5°, with a rate constant of 0.0352 sec-1 (Griffiths and Bender, 1972). An even larger rate enhancement is achieved upon inclusion of this material within the cyclohexaamylose cavity—fc2 = 0.16 sec-1. This fivefold acceleration cannot be satisfactorily explained either by a microsolvent effect which would be expected to depress the rate of the reaction or, at this pH, by covalent... 

The dimerisation energy for derivatives of 2 (ca. 35 kJ mol-1) is considerable, particularly in relation to the strength of intermolecular forces and some persistence is required in order to isolate derivatives of 2 which do not form 7T —7r dimers in the solid state. A survey of the monomeric derivatives has been published recently.26 Since the spin density distribution in 2 is rather insensitive to chemical tuning, approaches to inhibit dimerisation rely exclusively on structural modifications, which affect the nature of the intermolecular forces. Inclusion of sterically demanding groups, such as 13, 14 and 15 has proved partially successful (in the case of the diradical 14 one ring is involved in formation of a dimer, while the other retains its open shell character). 

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