Molecular structures proton ordering

The indazole molecular structure (Figure 11) shows the tautomeric proton bonded to N-1 (1//-indazole. Section 4.04.1.5.1). A linear correlation between the bond lengths and the bond orders calculated by the CNDO/2 method was observed (74T2903). 

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 molecular structure of retinoic acid is typical for an amphiphilic compound that is concentrated at interfaces. Further, the carboxylic acid groups allow such compounds to adjust their amphiphilic character by the degree of their dissociation. Surface tension measurements were carried out in order to determine the surface activity of retinoic acid [179]. The surface tension with respect to the concentration at pH 5 decreases more strongly than at pH 9. This reflects the fact that the protonated form of retinoic acid is more efficient in its surface activity than the deprotonated form. The critical micelle concentrations are 3.7 0.5 mg/L (pH 5) and 19 2 mg/L (pH 9). The limiting surface tension values in both curves is about 35 mN/m. Due to the precipitation of retinoic acid, the highest concentration in the surface tension curve at a pH of 5 was 20 mg/L. By contrast the solubility at pH 9 is at least 1 g/L. In order to verify the results from the FTIR measurements, films of the complexes were immersed in a solution of 0.15 mol/L sodium... 

Fig. 3.4. Oxygen positions in Ice III and its proton-ordered analogue Ice IX. The drawing is a projection along the c-axis with heights above the projection plane given in hundredths of the c-axis (c = 6-83 A). (Kamb, 1968.) (From Structural Chemistry and Molecular Biology, ed. Alexander Rich and Norman Davidson. San Francisco Freeman Co., copyright 1968.)...

The effect of interlocking on the properties of molecules is dramatic. For example, the basicity of the 2,9-diphenyl-1.10-phenanthroline unit is enhanced by several orders of magnitude when it is present in a [2]catenand. The proton catenate displays a similar molecular structure to that of the corresponding copper(I) catenate, whereas that of the catenand is completely different. The special topology of the catenands and knots makes them unique ligands, with strong complexes being formed with a variety of metal ions. ° ... 

Gp is the only known host giving 25 types of the different isostructurai supramolecular complexes (clathrates). This natural compound demonstrates dozens of kinds of biological activity. Such behavior is explained by its special molecular structure—diversity of the polar functional (six proton-donor and two proton-acceptor) groups, conformational mobility, and racemicity. This finding may be used in the future in order to design or look for the new versatile host compounds. 

Replacement of the acid proton (N-H) by a methyl group in this molecular structure has the same side effects as a result, the compound will be similarly sensitive to the polarity and acidity of the medium, but not to its basicity owing to the absence of an acid site. Consequently, l-methyl-5-nitroindoline (MNI, 10) possesses the required properties for use as a homomorph of 5-nitroindoline in order to construct our solvent basicity scale (SB). The suitability of this probe/homomorph couple is consistent with theoretical MP2/6-31G data. Thus, both the probe and its homomorph exhibit the same sensitivity to solvent polar-ity/polarizability because of their similar dipole moments (p i = 7.13, = 7.31 D) and... 

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