Mutual Positioning Research Articles

Intramolecular Hydrogen Bonding and Molecular Structure of 2,5-Dihydroxyterephthalaldehyde and 4,6-Dihydroxyisophthalaldehyde: A Gas-Phase Electron Diffraction and ab Initio Molecular Orbital Study

The molecular structure of 2,5-dihydroxyterephthalaldehyde has been determined from a joint electron diffraction/ab initio investigation, and the molecular structure of 4,6-dihydroxyisophthalaldehyde has been obtained from ab initio calculations at the MP2/6-31G* level. There is considerable intramolecular hydrogen bonding in these structures manifested by the O···H and O···O distances as well as by the structural changes in the rest of the molecule. These changes are consistent with the notion of resonance-assisted hydrogen bonding. The hydrogen bonding is somewhat stronger in 4,6-dihydroxyisophthalaldehyde than in 2,5-dihydroxyterephthalaldehyde, and this difference may be linked to the difference in the mutual positioning of the interacting formyl and hydroxy groups in these molecules.

Tests on a 3 GHz ground plane Yagi

Classical dimensioning of a ground plane Yagi antenna for 3 GHz leads to a gain which is 2-3 dB less than predicted, but this can be overcome to some extent by additional directors. The impedance matching strongly depends on the size of the reflector, which should be by a factor of 1.2 longer than given by classical theory. The shape and size of the ground plane itself can be varied considerably with little or no effect on either the radiation pattern or the impedance characteristics but, on the other hand, inaccurate mutual positioning of the individual elements has a drastic influence. Material conductivity is not of prime concern.

Who Works with Whom? Interest Group Alliances and Opposition

Interest-group interactions may be examined in ways comparable to the analysis of conflict and coalition in other areas of political science. We seek to measure and compare the structure of interest-group participation and conflict in four domains of U.S. domestic policy: agriculture, energy, health, and labor. Data are drawn from a survey of 806 representatives of organizations with interests in federal policy, supplemented by interviews with 301 government officials in the same four domains. Several types of data are adduced regarding the intensity and partisanship of group conflict in each domain and the range and variety of group participation. Coalitional patterns are described and the mutual positioning of different kinds of organization—peak-association groups versus more specialized trade, professional, or commodity groups, for example—are examined.

On the relative heat stability of polyamides containing m- and p-carborane fragments

A study has been made of the heat stability of polyamides containing m- and p-carborane fragments in the acidic as well as in the amino components. It is shown that at elevated temperatures the behaviour of the polymers is greatly influenced not only by the isomery of the carborane nucleus, but also by mutual positioning of the latter and of the NH group of the amide bond.

Effect of crystallite shape on low-angle x-ray scattering

THER~ is considerable diversity in the low-angle X-ray diffraction patterns obtained from oriented crystalline polymers. Considerable changes in the intensity, shape and mutual positioning of the individual reflections occur during heat treatment and in the processes of elongation and contraction. These changes are a result of structural processes occurring in polymers at a level of hundreds or thousands of Angstroms. Despite a large number of investigations, the question of the structural interpretation and classification of the various types of low-angle reflection still remains unclear and further experiments need to be carried out in order to solve this problem. We shall briefly discuss the principal types of reflection that occur on low-angle X-ray diffraction patterns of oriented polymers. A single general term is frequently used for all these reflections: the long period. A reflection in the form of a striation intersecting the meridian of the X-ray diffraction pattern appears most frequently on low-angle diffraction patterns, the maximum intensity of the striation being

Potentiometric titration of polyacrylic acid, polymethacrylic acid and poly- l-glutamic acid

Potentiometric titration is a sensitive method of investigating the structure of polyelectrolytes. Despite the fact that the course of the titration curves is determined both by the mutual positioning of the charge groups on the polymer chain, and also by the ionic environment, and also that the interpretation of the titration curves may not always be carried out simply, the general course of the curves makes it possible to draw certain conclusions about the structure of the macromolecules. In the present work, a comparative investigation of a number of poly-acids has been carried out by the method of potentiometric titration at various ionic strengths; the poly-acid were: polyacrylic (PAA), polymethacrylic (PMAA) and poly- L-glutamic (PGA). The molecules of PAA and PMAA, despite their similar in chemical structure, differ markedly in a number of physical properties (see, for example, [1–4]), which the authors explain by the presence of intramolecular hydrogen bonds in PMMA and their absence in PAA. PGA represents a typical synthetic polypeptide, which has a helical configuration in the weakly ionized condition.