Molecular structure relative configuration

Table 2.14 summarizes the steps by which molecular structures can be determined using the NMR methods discussed thus far to determine the skeleton structure, relative configuration and conformation of a specific compound. 

One functional group and three substructures given by the H NMR spectrum 8 make up the molecular structure including the relative configuration of the sample compound. 

Thermal Properties. Before considering conventional thermal properties such as conductivity it is appropriate to consi r briefly the effect of temperature on the mechanical properties of plastics. It was stated earlier that the properties of plastics are markedly temperature dependent. This is as a result of their molecular structure. Consider first an amorphous plastic in which the molecular chains have a random configuration. Inside the material, even though it is not possible to view them, we loiow that the molecules are in a state of continual motion. As the material is heated up the molecules receive more energy and there is an increase in their relative movement. This makes the material more flexible. Conversely if the material is cooled down then molecular mobility decreases and the material becomes stiffer. 

A molecule is composed of a certain number N of nuclei and usually a much larger number of electrons. As the masses of the electrons and the nuclei are significantly different, the much lighter elections move rapidly to create the so-called electron cloud which sticks die nuclei into relatively fixed equilibrium positions. The resulting geometry of die nuclear configuration is usually referred to as the molecular structure. The vibrational and rotational spectra of a molecule, as observed in its infrared absorption or emission and the Raman effect, are determined by this molecular geometry. 

The stabilization of well-defined peptide microstructures is an important challenge in bioorganic chemistry. As the presented results show, metal coordination can be a simple but very effective tool for reaching this goal and fixing three dimensional molecular structures. The conformational (and stereochemical) information which is embedded in configurationally stable metal complex units can be transferred to amino acid residues or even to relatively large peptides and can induce helical-, sheet- or as discussed turn-type structures. 

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