Chains, of molecules

In addition to the size of the molecules and their distribution, the shapes or structures of individual polymer molecules also play an important role in determining the properties and processability of plastics. There are those that are formed by aligning themselves into long chains of molecules and others with branches or lateral connections to form complex structures. All these forms exist in either two or three dimensions. 

The structure of the trimer [Au3(NC5H4)3] has been studied and shows that individual molecules self-associate through aurophilic interactions into two distinct structural motifs that involve both extended chains of molecules connected by pairwise and individual Au---Au contacts, and discrete dimers linked by pairwise Au---Au interactions (Figure 25).3131... 

Molecules can link together in one dimension to form chains (threads), or in two dimensions to form membranes, or in three dimensions to form blocks. Hardness has meaning only for the last case. Long chains of molecules constitute polymers and will be discussed in the next chapter. Small molecules formed of a few atoms are gases or liquids at room temperature, so hardness has no meaning for them. 

So what does all of this have to do with polymers Natural, unheated rubber is a polymer, so it has long chains of molecules with some cross-links. When rubber is heated and sulfur is added to it, the sulfur forms many more cross-links between the chains, making it very strong. Rubber is elastic—it bounces back—because the chains are coiled into loops that can stretch out as the rubber bends or stretches, then coil back up when they re released. 

What s DNA Deoxyribonucleic acid, the helical ladderlike chain of molecules that makes up genes. DNA consists of a sugar molecule called deoxyribose (it is somewhat related to glucose), a nitrogen-containing molecule called a base, and phosphate atoms bonded to the other two components. It is the sequence of base pairs (one base on each strand) in DNA that determines the end-product (e.g., protein). The human genome— the entire DNA content of a human being—contains approximately 3 billion base pairs. 

The, crystal can correspondingly be easily cleaved into layers, this cleavage not breaking any of the hydrogen bonds. In the /3 form of the crystals there are long chains of molecules, with the structure... 

There are many different polymers which are long chains of molecules linked by covalent bonds. The chains can be either intertwined in a loose assembly, or they can be cross-linked by covalent bonds to form a very strong lattice. Chromophoric molecules can be included in polymers in two different ways they can be dispersed at random, rather like in a glassy matrix, or they can be part of the polymer chains themselves. 

Assuming that the Earth s radius is 6378 km, and that a molecule of benzene may be treated as a disc of radius 300 pm, calculate the mass of benzene needed to create a chain of molecules around the equator of the Earth. 

Thermoplastics consist of long chains of molecules, in the case of PE these are unbranched. Many of these chains together form a tangle which is more difficult to unravel the more branched the chains are. The branches are like hooks which cause the molecules to catch. Under the influence of relatively small external forces chains and parts of chains can slide across each other. PE is for instance used to make containers, chemical tubing and blow-moulded bottles. Some other thermoplastics are polypropylene (crates), polyvinyl chloride PVC (pipes) and polystyrene (foam). 

Plastic is a synthetic material made largely of chains of molecules bonded together during complex chemical reactions. Most plastics... 

Chemical separation of the chains of molecules in plastics usually involves a phase change. The process uses chemical reactions to change the order of molecules in a plastic, sometimes producing a liquid, gas, or another solid. 

Heat is also used to separate the chains of molecules in plastics physically. When plastics are heated, the molecules gather enough energy to break away from their chains and solid structures. Like chemical separation, melting can result in new liquids, gases, or other solids. These new liquids, gases, and solids are then used as raw ingredients to construct new plastic products. 

Figure 5 View of one layer of the structure of solvent-free 7, close to the be plane, showing the parallel chains of molecules running vertically (along b). These are linked by means of OFF and EF interactions.

Figure 44. Supramolecular association in the orthorhombic form of Ni(S2COEt)2 (a) showing the links between alternating chains of molecules in the ab plane, (b) viewed down the axes of the chains, and (c) showing the connectivity between the tetragonally distorted octahedral units.

Cu(tfd)2 units by 0.015 A in an orthogonal direction to fill in the space vacated by the TTF molecules. This existence of a progressive dimerization in a regular chain of molecules of spin 1/2 along with the observed activated temperature dependence of the magnetic susceptibility below Tc has been interpreted in terms of a spin-Peierls instability77-78) in a one-dimensional antiferromagnetically coupled chain. 

In order to illustrate the importance of these more distant interactions we choose a simple model system, a linear chain of molecules. We start with the trimer. From Eqs. (8) and (9) we obtain ... 

Let us now consider systems formed by polar molecules, e.g. HF, H20 and HC1. The HF and HC1 crystals contain one-dimensional bent chains of molecules between which the mutual interactions are relatively weak (Fig. 12). In the case of HF we observe a marked decrease of the intermoleeular distance (ARpp 0.3 A) upon the formation of the solid phase. Ice I has a fairly complicated three-dimensional structure (Fig. 12), dipoles appear at different relative orientations, and the infinite chain is no appropriate model. Nevertheless, the contraction of the intermoleeular distance in the solid state is substantial (ARoo 0-24 A). In both cases, the stabilizing contributions have to be attributed to attractive many-body forces since the changes observed exceed by far the effects to be expected in polar systems with pairwise additive potentials. The same is true for the energy of interaction (Table 12) ... 

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