Chemical structure, acid-base behavior

In recent years, the relaxation and yield behavior of amorphous semi-aromatic polyamides has been the subject of a detailed analysis at the molecular level [1-6], Two series of materials were investigated, so-called SAPA-R and SAPA-A (Table 1). In the SAPA-R series, the chemical structure is based on isophthalic or terephthalic acid and 2-methyl 1,5-pentanediamine. In the SAPA-A series, the chemical formulae include isophthalic or terephthalic acid residues, diamino dimethylcyclohexylmethane residues, and lactam-12 sequences. 

ACID-BASE BEHAVIOR AND CHEMICAL STRUCTURE We explore the relationship between chemical structure and acid-base behavior. 

When a substance is dissolved in water, it may behave as an acid, behave as a base, or exhibit no acid—base properties. How does the chemical structure of a substance determine which of these behaviors is exhibited by the substance For example, why do some substances that contain OH groups behave as bases, releasing OH ions into solution, whereas others behave as acids, ionizing to release H ions In this section we discuss briefly the effects of chemical structure on acid—base behavior. 

SECTION 16.10 Acid-Base Behavior and Chemical Structure 705... 

Despite large structural differences among amino acids and peptides, their log Kh values in bulk aqueous solution are very similar. In micellar media, the effect of chemical structure on log Kh is much more pronounced (Table 5.4), which is indicative of the profound influence of solute-micelle interactions on the acid-base behavior of these compounds [44]. The apparent protonation constant in micellar media is expressed as ... 

The ELS detector was previously also referred to as a mass detector, pointing to the fact that the response is (mainly) determined by the mass of the sample rather than by its chemical structure. Van der Meeren et al., though, demonstrated that the ELSD calibration curves of phospholipid classes were also dependent on the fatty acid composition (52). The dependence on the fatty acid composition is, however, completely different in nature and much less pronounced than for UV detection. The reason for this behavior is to be found in the partial resolution of molecular species, even during normal-phase chromatography. Thus, the peak shape depends not only on the chromatographic system but also on the fatty acid composition and molecular species distribution of the PL sample (47). Because it was shown before, based on both theoretical considerations and practical experiments, that the ELS detector response is generally inversely proportional to peak width (62,104), it follows that the molecular species distribution of the PL standards used should be similar to the sample components to be quantified. It was shown that up to 20% error may be induced if an inappropriate standard is used (52). 

The presence of acidic functional groups, mostly carboxyl and phenolic OH groups, in the molecular structure of soil HS renders them major players in the acid-base buffering capacity of soils and in the fate, bioavailability, and physico-chemical behavior of macro- and micronutrients, toxic metal ions, and several xenobiotic organic compounds in soil (Ritchie and Perdue, 2003 Senesi and Loffredo, 2005). Consequently, the effects of amendment on the acid-base properties of soil HAs and FAs is a subject of considerable interest. 

The two parts of the present volume contain seventeen chapters written by experts from eleven countries. They cover computational chemistry, structural chemistry by spectroscopic methods, luminescence, thermochemistry, synthesis, various aspect of chemical behavior such as application as synthons, acid-base properties, coordination chemistry, redox behavior, electrochemistry, analytical chemistry and biological aspects of the metal enolates. Chapters are devoted to special families of compounds, such as the metal ynolates and 1,2-thiolenes and, besides their use as synthons in organic and inorganic chemistry, chapters appear on applications of metal enolates in structural analysis as NMR shift reagents, catalysis, polymerization, electronic devices and deposition of metals and their oxides. 

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