Functional groups states

The diacid-diamine amidation described in reaction 2 in Table 5.4 has been widely studied in the melt, in solution, and in the solid state. When equal amounts of two functional groups are present, both the rate laws and the molecular weight distributions are given by the treatment of the preceding sections. The stoichiometric balance between reactive groups is readily obtained by precipitating the 1 1 ammonium salt from ethanol ... 

The concept of the principal function raises the question of how priority is deterrnined when two or more different functional groups are present. No arbitrary rule can be entirely satisfactory, but an order has been codified in lUPAC recommendations (52—54), and an essentially similar order is used by Chemical Abstracts Service. In general, a higher state of oxidation takes precedence over a lower one, as shown in Table 1. 

Internal and External Phases. When dyeing hydrated fibers, for example, hydrophUic fibers in aqueous dyebaths, two distinct solvent phases exist, the external and the internal. The external solvent phase consists of the mobile molecules that are in the external dyebath so far away from the fiber that they are not influenced by it. The internal phase comprises the water that is within the fiber infrastmcture in a bound or static state and is an integral part of the internal stmcture in terms of defining the physical chemistry and thermodynamics of the system. Thus dye molecules have different chemical potentials when in the internal solvent phase than when in the external phase. Further, the effects of hydrogen ions (H" ) or hydroxyl ions (OH ) have a different impact. In the external phase acids or bases are completely dissociated and give an external or dyebath pH. In the internal phase these ions can interact with the fiber polymer chain and cause ionization of functional groups. This results in the pH of the internal phase being different from the external phase and the theoretical concept of internal pH (6). 

Flammability Timits. Some 1358 compounds selected from the DIPPR Compilation Pile (Peimsylvania State University, 1991 Ref. 4) have been fit for upper and lower flammabiHty limits (227). Average errors reported were 0.266% (volume) and 0.06% (volume) for upper and lower flammabiHty limits, respectively. A detailed analysis by functional group classification is included that identifies classifications with high error for several methods. 

Determination of surface functional groups, e.g., —OH, —C - C—, and >C = O, and identificadon of adsorbed molecules comes principally from comparison with vibrational spectra (infixed and Raman) of known molecules and compounds. Quick qualitative analysis is possible, e.g., stretching modes involving H appear for v(C—H) at 3000 cm and for v(0—H) at 3400 cm L In addition, the vibrational energy indicates the chemical state of the atoms involved, e.g., v(C=C) " 1500 cmT and v(C=0) " 1800 cm"L Further details concerning the structure of adsorbates... 

This expression has the same form as Eqs. (6-81) and (6-84). Here, of course, the substrate is not protonated to an appreciable extent. With other suitable experiments and some luck, the steady-state situation can be distinguished from substrate titration. For example, is the pKa value deduced under the assumption of a titration reasonable for the molecule in question That is, is it reasonable for one of the functional groups of A to have a pKa near the pH of the bend Can one detect significant amounts of two species, AH+ and A, at a pH near the presumed pKal Can one modify the substrate, eliminating the site of protonation If so, and if a titration mechanism operates, then (as the reader should show) the pH profile should become linear. Obviously, were substrate titration and a steady-state intermediate situation to coexist in the same system, a more complicated but not intractable situation would result. 

A secondary kie is one that arises from other bonds in the reactive molecule. Obviously, these are much weaker effects than those we have been considering. If they are found, it may suggest that the functional group distorts or twists considerably in the transition state, even though it is not changed in the reaction. 

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