Structural units Multiplicity

An understanding of crystallization is important for the systematic development of crystal engineering, but it is not a simple phenomenon and many would agree that it is still far too difficult to study in a rigorous way, either experimentally or theoretically. However, indirect approaches to the study of crystallization are evolving. Three possible types of crystals that may be pertinent to this endeavor are (1) polymorphs - these represent cases of alternative crystallization, (2) pseudosymmetric structures with multiple molecules in the asymmetric unit - these could represent cases of incomplete crystallization, and (3) solvated crystals or pseudopolymorphs -these may represent cases of interrupted crystallization. These three scenarios are now sketched very briefly and the treatment given is necessarily selective. 

Small granular structural unit that serves as the basic building block of the thylakoid membrane and contains multiple chlorophyll molecules as well as cytochromes. 

In replacement a nomenclature as conventionally applied to acyclic structures with multiple heteroatoms, terminal heteroatoms are not designated with a prefixes but are named as characteristic groups of the structure, i.e., as hydroxy, amino, carboxylic acid, etc. However, heteroatoms in such positions within the constitutional units of ladder or spiro polymer molecules are not terminal units and the structures are not necessarily acyclic. Consequently, such atoms are designated with a prefixes, and thereby the simplicity afforded by the application of replacement nomenclature to polymer molecules is enhanced. 

Luminescence has already been considered in general terms in Chapter 5. Luminescent POPAM dendrimers of various generations with peripheral dansyl units were studied by Balzani and Vogtle et al. as sensor model systems with regard to the fundamental suitability of dendritic structures for multiplication of signalling groups (multi-labelling) [48]. 

Values for only one structural unit have been reported in cases where multiple units are contained within the unit cell. b Average values. 

The formal definition of a homopolymer is a polymer derived from one species of monomer. However, the word homopolymer often is used more broadly to describe polymers whose structure can be represented by multiple repetition of a single type of repeat unit which may contain one or more species of monomer unit. The latter is sometimes referred to as a structural unit. 

Alkenes with the structural unit R2C=C— would give [R2C(OH)2] —=— R2C=0. Multiple-bonded C s bonded only to H s would form [C(OH)4], which loses two molecules of H20 to give C02. 

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