Supermolecule, definition

Paraphrasing Corey s historic definition of synthon [203], Desiraju defined a supramolecular synthon as a structural unit within a supermolecule that can be formed or assembled by known or conceivable synthetic operations involving intermolecular interactions [204], The robustness of the XB has allowed several supramolecular synthons based on this interaction to be identified and some examples have been presented in this chapter. 

For many chemists LCs are mysterious and complex materials, their very definition defying a simple understanding. The basic idea behind this discussion of stereochemistry in LCs is that molecules and LCs represent the same phenomenon. Liquid crystals are supermolecules in a different way than are supramolecular assemblies. Indeed, LCs can be composed of supramolecular... 

By comparing Hynes s and Rivail s models some common points and some differences are evident. Both studies use an HC1-H20-H20 unit as solute which is treated as a supermolecule in a QM description. Both of them introduce a one-dimensional adiabatic representation of the proton transfer potential but, while Rivail assumes solvent equilibration along the whole proton transfer path, Hynes uses a fixed, but appropriate, solvent configuration. The definition of appropriate configuration is reached using some concepts that are not present in Rivail s treatment, i.e. the crossing of two YB structures ( reactant and product ) in the space of solvent dynamical coordinates. 

As all intermolecular interactions, except covalent bond formation (a very special case of crystal engineering), are by nature supramolecular and the crystal itself can be considered as supermolecule par excellence [5, 6], Crystal Engineering can be defined as a set of designed processes which aim to a formation of a crystalline material utilizing the supramolecular interactions and self-assembly of the components , in a very short form making crystal by design [24]. The above definition does not include nor require any specific interactions, physical or chemical conditions, crystallization techniques, additives or serendipity [25],... 

The historical molecular bias of organic chemistry necessitates the reiteration that supermolecules are not just collections of molecules and that their structure and characteristic properties are distinct from the aggregate properties of their molecular constituents. Such a statement is, however, hardly necessary in inorganic crystal chemistry where structures have traditionally been viewed in terms of networks and connectivities and where the very definition of molecularity is excitingly different. And yet, these organic and inorganic viewpoints are only parts of the whole, and another manifestation of the synthesizing aspect of supramolecular chemistry is its... 

In conclusion, the definition of a subunit as innocent with respect to the interaction with light should be employed after careful inspection of the spectroscopic properties of the supermolecule and of the separated components, and after monitoring the occurrence of light-induced processes. As a practical short-cut, use of light at a selected frequency (for instance, a low-frequency radiation to selectively excite the lowest-available electronic levels of a supermolecule, both of localized or... 

The general treatment of the theory of chemical reactions presented in this book is based on the usual adiabatic separation of nuclear and electronic motions which permits a definition of the potential energy as a function of internuclear distances This approach proves to be very useful for the study of electronically adiabatic reactions, provided a separation of the rotation of the reacting system, treated as a supermolecule, is possible. In general, such a separation seems to be a bad approximation /10/. A consideration of the coupling of the overall rotation with the internal motions of the system means taking into account the possibility of non-adiabatic transitions from one to another potential energy surface. This is still an unsolved problem of theoretical chemistry which is open for discussion. 

According to the definition of supramolecular chemistry cited above, the smallest supermolecule can be a dimer at the other extreme we find very large, polymeric... 

Full Cl, as to be expected from a formally exact theory, is also size consistent. Unfortunately truncated Cl does not have this property. At first, this may appear surprising since size consistency seems like a rather modest requirement. This deficiency can however be understood by a simple example. Consider a supermolecule composed of two noninteracting H2 molecules. Why is it that the DCI energy of the supermolecule is not the sum of the DCI energies of the two monomers By definition the DCI wave function of each of the monomers contains double excitations within the monomer. If we restrict the supermolecule trial function to double excitations, we exclude the possibility that both monomers are simultaneously doubly excited, since this represents a quadruple excitation in the supermolecule. Thus the supermolecule wave function truncated at the DCI level does not have sufficient flexibility to yield twice the DCI monomer energy. 

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