Molecules and Substances

Understand the behavior of molecules and substances in unusual environments at extreme temperatures or pressures, absorbed on solid surfaces, or under shear flow. 

Understand the chemistry of molecules and substances in their excited states, or at or near their critical points, and at the nanoscale level in which surface characteristics can dominate bulk properties. 

As noted in Section 1.3, the terms molecule and substance tend to be used interchangeably by organic chemists, who are usually dealing with substances which consist of discrete molecules. There is a tendency among students to do likewise in inorganic chemistry. This harks back to the late nineteenth century, when inorganic chemists were accustomed to... 

V. M. Tatevskii, The Theory of Physicochemical Properties of Molecules and Substances., MSU Publishing House, 1987. 

Molecules and substances that exhibit optical activity are generally described as chiral (Greek cheir hand ). Two crystals of the same substance that are... 

However, many substances, notably alcohols, have a greater proton affinity than the hydrogen fluoride molecule, and so behave as bases, for example ethanol ... 

Furthermore, most physicochemical properties are related to interactions between a molecule and its environment. For instance, the partitioning between two phases is a temperature-dependent constant of a substance with respect to the solvent system. Equation (1) therefore has to be rewritten as a function of the molecular structure, C, the solvent, S, the temperature, X etc. (Eq. (2)). 

The analyses which follow are arranged in the order in which they would be applied to a newly discovered substance, the estimation of the elements present and molecular weight deter-minations(f.e., determination of empirical and molecular formulae respectively) coming first, then the estimation of particular groups in the molecule, and finally the estimation of special classes of organic compounds. It should be noted, however, that this systematic order differs considerably from the order of experimental difficulty of the individual analyses. Consequently many of the later macro-analyses, such as the estimation of hydroxyl groups, acetyl groups, urea, etc. may well be undertaken by elementary students, while the earlier analyses, such as estimation of elements present in the molecule, should be reserved for more senior students. 

One of the most important characteristics of micelles is their ability to take up all kinds of substances. Binding of these compounds to micelles is generally driven by hydrophobic and electrostatic interactions. The dynamics of solubilisation into micelles are similar to those observed for entrance and exit of individual surfactant molecules. Their uptake into micelles is close to diffusion controlled, whereas the residence time depends on the sttucture of the molecule and the solubilisate, and is usually in the order of 10 to 10" seconds . Hence, these processes are fast on the NMR time scale. 

Induced dipole/induced dipole forces are the only intermolecular attractive forces available to nonpolar molecules such as alkanes In addition to these forces polar molecules engage m dipole-dipole and dipole/mduced dipole attractions The dipole-dipole attractive force is easiest to visualize and is illustrated m Figure 4 3 Two molecules of a polar substance experience a mutual attraction between the positively polarized region of one molecule and the negatively polarized region of the other As its name implies the dipole/induced dipole force combines features of both the induced dipole/mduced dipole and dipole-dipole attractive forces A polar region of one mole cule alters the electron distribution m a nonpolar region of another m a direction that produces an attractive force between them... 

Extensive intercalation of polar molecules takes place in this substance in an irreversible manner, and marked hysteresis results (Fig. 4.28). The driving force is thought to be the interaction between the polar molecules and the exchange cations present in the montmorillonitic sheets, since non-polar molecules give rise to a simple Type B hysteresis loop with no low-pressure hysteresis. 

In this chapter we examine the elastic behavior of polymers. We shall see that this behavior is quite different from the elasticity displayed by metals and substances composed of small molecules. This is a direct consequence of the chain structure of the polymer molecules. In many polymers elasticity does not occur alone, but coupled with viscous phenomena. The combination of these effects is called viscoelasticity. We shall examine this behavior as well. 

The various mechanical properties of polyamides may be traced in many instances to the possibility of intermolecular hydrogen bonding between the polymer molecules and to the relatively stiff chains these substances possess. The latter, in turn, may be understood by considering still another equilibrium, this one among resonance structures along the chain backbone ... 

Radiation, both in the uv and in the visible region, can have a highly destmctive effect by decomposing the dye molecule. Other substances, particularly water, can reinforce the photochemical effect of light. Once the dyed material fades, its original condition usually cannot be restored. 

Chemical degradation studies carried out on streptovaricias A and C, which are the primary components of the cmde complex, yielded substances shown ia Figure 1. Streptovaricia A (4), consumes two moles of sodium periodate to yield variciaal A [21913-68-8] (1), 0 2 200, which accounts for the ahphatic portion of the molecule, and prestreptovarone [58074-37-6] (2), C2C)H2C)N02, which accounts for the aromatic chromophore of the streptovaricias (Fig. 2). Streptovaricia G (9) is the only other streptovaricia that yields prestreptovaroae upoa treatmeat with sodium periodate. Treatmeat of streptovaricias A (4), B (5), C (6), E (8), and G (9) with sodium periodate and osmium tetroxide yields streptovarone [36108-44-8] (3), C24H23NO2, which is also produced by the reaction of prestreptovarone with sodium periodate and osmium tetroxide (4,65). A number of aliphatic products were isolated from the oxidation of streptovaricia C and its derivatives (66). 

The most striking feature of the earth, and one lacking from the neighboring planets, is the extensive hydrosphere. Water is the solvent and transport medium, participant, and catalyst in nearly all chemical reactions occurring in the environment. It is a necessary condition for life and represents a necessary resource for humans. It is an extraordinarily complex substance. Stmctural models of Hquid water depend on concepts of the electronic stmcture of the water molecule and the stmcture of ice. Hydrogen bonding between H2O molecules has an effect on almost every physical property of Hquid water. 

Anhydrous An anhydrous material does not contain any water molecules. Many substances occur naturally as hydrates, compounds that have a specific number of water molecules attached to them. This water can often be removed by heating and/or vacuum to give the anhydrous material. Anhydrous materials can absorb water from their surroundings and find use as dessicants. Examples include those packets of silica gel you find in some consumer goods, as well as dehumidifying sachets used in clothes closets. When an anhydrous material reacts with water, this could release a large amount of heat, possibly leading to a heat or pressure buildup that could result in an explosion. 

Starch A polymeric substance of glucose molecules and a component of many terrestrial and aquatic plants used by some organisms as a means of energy storage starch is broken down by enzymes (amylases) to yield glucose, which can be used as a feedstock for chemical or energy production. 

Coclaurine is of special interest since worcoclaurine (I MeO HO) can be regarded as the parent substance from which by ether formation the series of bisbenzylisoquinoline alkaloids can arise. Thus, the dauricine type of alkaloid may be formed by a single ether linkage between the 4 -hydroxyl of one woreoclaurine molecule and a hydrogen atom ortho to the 4 -hydroxyl of a second molecule. 

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