Simple molecular structures

Despite its very simple molecular structure, many characteristics of water are still poorly understood... 

All gases and most liquids of simple molecular structure exhibit what is termed Newtonian behaviour, and their viscosities are independent of the way in which they are flowing. Temperature may, however, exert a strong influence on viscosity which, for highly viscous liquids, will show a rapid decrease as the temperature is increased. Gases, show the reverse tendency, however, with viscosity rising with increasing temperature, and also with increase of pressure. 

Benouazzane, M., Coco, S Espinet, P. and Barbera, J. (2001) Supramolecular organization in copper(I) isocyanide complexes Copper(I) liquid crystals from a simple molecular structure. Journal of Materials Chemistry, 11, 1740-1744. 

General anesthetics are usually small solutes with relatively simple molecular structure. As overviewed before, Meyer and Overton have proposed that the potency of general anesthetics correlates with their solubility in organic solvents (the Meyer-Overton theory) almost a century ago. On the other hand, local anesthetics widely used are positively charged amphiphiles in solution and reversibly block the nerve conduction. We expect that the partition of both general and local anesthetics into lipid bilayer membranes plays a key role in controlling the anesthetic potency. Bilayer interfaces are crucial for the delivery of the anesthetics. 

The hydrogen halides are colourless gases at room temperature and pressure. They produce steamy fumes in moist air. They are covalently bonded molecules, with simple molecular structures. They are very soluble in water, as they react to form ions. 

In addition, G and F matrix elements have been tabulated (see Appendix VII in Nakamoto 1997) for many simple molecular structure types (including bent triatomic, pyramidal and planar tetratomic, tetrahedral and square-planar 5-atom, and octahedral 7-atom molecules) in block-diagonalized form. MUBFF G and F matrices for tetrahedral XY4 and octahedral XY molecules are reproduced in Table 1. Tabulated matrices greatly facilitate calculations, and can easily be applied to vibrational modeling of isotopically substituted molecules. Matrix elements change, however, if the symmetry of the substituted molecule is lowered by isotopic substitution, and the tabulated matrices will not work in these circumstances. For instance, C Cl4, and all share full XY4 tetrahedral symmetry (point group Tj), but... 

Squaric acid (H2SQ) has been chosen as a first test compound because it has a very simple molecular structure. Planar sheets of the squarate (C4O4) groups are linked to each other in a two-dimensional network through O - H...0 bonds (Fig. 1) with weak van der Waals forces [52,53]. The protons perform an order/disorder motion above the antiferroelectric phase transi-... 

The interpretation, of the diffraction effects of gases of simple molecular structure is simplified by the fact that the molecules are very far apart, and therefore it is necessary to consider only the distances between the atoms in one molecule. Much information on the structures of molecules has been gained in this way by Debye and others. The subject is well treated in a book by Pirenne (1946). 

Bismuth is the fifth member of the nitrogen family of elements and, like its congeners, possesses five electrons in its outermost shell, 6s 6p. In many compounds, the bismuth atom utilizes only the three 6p electrons in bond formation and retains the two 6x electrons as an inert pair. Compounds are also known where bismuth is bonded to four, five, or six other atoms. Many bismuth compounds do not have simple molecular structures and exist in the solid state as polymeric chains or sheets. 

Fig. 6.1 Some simple molecular structures in which all electrons on the central atom form bonding pairs, (a) carbon dioxide, with two Sp a bonds (solid lines) and two n bonds ...

Some animals, and especially insects, rely on what amounts to a sense-of-smell for communication with others of their species. Substances synthesized by a particular species, and used to send messages in this way, are called pheromones. Many of these substances have rather simple molecular structures because they must be reasonably volatile and yet they are remarkably specific... 

Simple molecular structures are simple, formed from only a few atoms. They have strong covalent bonds between the atoms within a molecule (intramolecular bonds) but have weak bonds between the molecules (intermolecular bonds). 

I will show, in a two-dimensional example, how to construct the Patterson map from a simple crystal structure and then how to use a calculated Patterson map to deduce a structure (Fig. 6.10). The simple molecular structure in Fig. 6.10a contains three atoms (dark circles) in each unit cell. To construct the Patterson map, first draw all possible vectors between atoms in one unit cell, including vectors between the same pair of atoms but in opposite directions. (For example, treat 1 —> 2 and 2 — 1 as distinct vectors.) Two of the six vectors (1 — 3 and 3 —> 2) are shown in the figure. Then draw empty unit cells around an origin (Fig. 6.10b), and redraw all vectors with their tails at the origin. The head of each vector is the location of a peak in the Patterson map, sometimes called a Patterson "atom" (light circles). The coordinates (u,v,w)... 

If water or some other compound with a simple molecular structure has been studied, it is possible to combine the entropy of vaporization, A5 = AHyl T, with the third-law calorimetric entropy of the liquid to obtain a thermodynamic value for the entropy of the vapor. The statistical mechanical value of Sg can be calculated using the known molar mass and the spectroscopic parameters for the rotation and vibration of the gas-phase molecule. A comparison of Sg (thermodynamic) with Sg (spectroscopic) provides a test of the validity of the third law of thermodynamics. The case of H2O is particularly interesting, since ice has a nonzero residual entropy at 0 K due to frozen-in disorder in the proton positions. ... 

Question 13.1 Suggest why, at the time of the Manhattan project in the 1940s, Gilman attempted the synthesis of simple uranium alkyls and aryls as vehicles for isotope separation. Answer 13.1 At that time, few d-block alkyls and aryls were known. Gilman would have reasoned that by analogy with compounds of the Group IV elements like carbon and silicon, uranium(iv) alkyls and aryls might have simple molecular structures and thus be volatile. 

Water is one of the most familiar material in our life and is indispensable to all living things. In contrast to its apparently simple molecular structure, water shows many anomalous properties from both macroscopic and microscopic points of view. However, the basic physical property of water, for example the dynamical structure of water, has not yet been fully clioified. To un rstand the dynamical aspect of water structure and its significant role in life, it is essential to clarify not only the dynamics of water molecules themselves but also the dynamics of water in the aqueous solutions. 

Equation (16.1) provides semi quantitative representations of thennodynamic and transport properties for nonpolar substances of relatively simple molecular structure. In Eq. (16.1), the term is supposed to represent bimolecularrepulsions, and the tenn bimolecular attrac-... 

Burden, F.R. (1996). Using Artificial Neural Networks to Predict Biological Activity of Molecules from Simple Molecular Structural Considerations. Quant.Struct.-Act.Relat., 15, 7-11. 

Electron diffraction and spectroscopic studies show that in the gaseous state the halides 81X4 form tetrahedral molecules the simple molecular structure of SiF4 in the crystalline state has been confirmed by an X-ray study at -145°C. ... 

As described here, MaNP acid has excellent enantioresolving power despite its simple molecular structure and the absence of so-called hetero atoms. Furthermore, the chiral acid 3 is superior to Mosher s MTPA and Trosfs MPA acids in the magnetic anisotropy effect. 

The exhaustion of disperse dyes, at equilibrium, is quite good, but the diffusion into the fibre is extremely slow. I he time required to reach equilibrium, therefore, is much longer than would be permissible in practice. By selecting disperse dyes with the most rapid rates of diffusion it is possible to dye pale to medium shades at the boil within a reasonable time. Dyestuffs which are suitable are shown below- and it will be observed that they all possess simple molecular structure. 

The dielectric properties of substrates depend heavily on the chemistry of the constituent raw materials. The presence of polar chemical groups within the molecules increases the dielectric constant. The relatively simple molecular structures of polyethylene (CH2 - CH2) and polytetrafluorethylene (CF2 - CF2) would be expected to have low dielectric constants. Epoxy resins and polyimides have relatively high dielectric constant values since they have complex molecular structures. 

This posetic approach thence provides a novel approach to struc-ture/property and structure/bioactivity correlations, with focus in some sense beyond simple molecular structure, in that this approach attends to how a structure fits into a systematic (reaction) network of structures. Different manners for fitting and prediction of properties are noted, with illustration of an especially simple poset-average scheme. Some numerical evidence indicates that such approaches are quite reasonable. It is emphasized that such directed reaction graphs admitting posetic treatment are widespread. 

We have but little knowledge of the status prevailing in the adsorbed layer, especially in liquid systems. Even when only a few components are present and the substances involved have a simple molecular structure, clues as to the nature of the adsorbed layer usually admit varied interpretations. Fortunately in industrial applications, information as to the status of the adsorbed substance is seldom needed except when catalysis or subsequent elution is involved. 

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