Acidity Cations

Polymerization to Polyether Polyols. The addition polymerization of propylene oxide to form polyether polyols is very important commercially. Polyols are made by addition of epoxides to initiators, ie, compounds that contain an active hydrogen, such as alcohols or amines. The polymerization occurs with either anionic (base) or cationic (acidic) catalysis. The base catalysis is preferred commercially (25,27). 

In order to account for the inability of many enzymes to bind the protonated form of the basic inhibitors or permanently cationic ones better than uncharged analogs (for example, yS-o-galactosidase from E. coli, and P-v>-glucosidase from almonds), it was proposed that the enzyme could proton-ate the inhibitor at the active site by a cationic acid (for example, protonated histidine). If proton transfer cannot occur, the attractive forces due to the carboxylate would be canceled by the repulsion from the cationic acid. Experimental evidence for this proposal is, however, still lacking. In fi-D-gn-lactosidase from E. coli, a tyrosine is presumed to be responsible for the protonation of substrates. ... 

According to the principle of extraction, the organic extractants can be classified into four classes (i) solvating (neutral) (ii) cationic (acidic) (iii) anionic (basic) and (iv) chelating. The trade names and chemical names of the various extractants have been presented in the figures illustrating the classification. 

Nickel and Weber [30] reported aqueous titrations of carboxylic acids, phenols, acidic drugs containing NH groups, cationic acids (ammonium salts) in dimethyl-formamide solution against 0.1 M potassium hydroxide aqueous solution as the... 

Keywords Infrared spectroscopy, LTA, divalent cation, acidity, cokage... 

The catalytic constants for acids in aqueous solution correlate well with pK, and there is no apparent difference between uncharged and cation acids (carboxylic acids and pyridinium cations), though some steric inhibition is evident for 2,6-substituted pyridinium cations. The catalytic constants for bases behave somewhat more erratically, and it has been suggested by Gruen and MoTigue (1963b) that errors are intro-... 

Since the acid HX acts as a solvent, its activity may be regarded as constant and included in the equilibrium constant. is the mean activity coefficient of the cation acid and the stabilizing anion X. The way in which equations (5) and (6) are written define the corresponding equilibrium constants as basicity constants K. Their reciprocal corresponds to the acidity constant and gives the acid strength of the conjugate acid AH. ... 

On the other hand, the ionization of a cationic acid (equation 5.39) is insensitive to solvent polarity, since there is no change of charge in the equilibrium. 

This reaction is an dehydration acid-catalyzed.12 The hexaaquocop-per cation behaves as a weak cationic acid in copper-salt solution.13 Protonation of the hydroxy group produces an oxonium ion that decomposes unimolecularly into carbocation 21 and water. Water is removed from the reaction equilibrium by means of a water-separating device. Carbocation 21 eliminates an -proton with formation of the energetically favorable conjugated diene 9. 

Entries 8 and 9 involve cationic acids with the main resonance structure of the conjugate base being neutral, e.g., 10b. Hence hydrogen bonding solvation plays a minimal role and there... 

Acidic Carboxonium Ions (Hydroxylated Cations). Acidic carboxonium ions are generally obtained by protonation of carbonyl compounds.541,542 Aldehydes and ketones protonate on the carbonyl oxygen atom in superacid media at low temperatures, and the corresponding carboxonium ions can be directly observed543-551 [Eqs. (3.61) and (3.62)]. 

Esters are named similarly, with the name of the alkyl or aryl radical replacing the name of the cation. Acid esters of acids and their salts are named as neutral esters, but the components are cited in the order cation, alkyl or aryl radical, hydrogen, and anion. Locants are added if necessary. For example,... 

Cationically catalyzed polymerizations28,72 have not received as much attention as the anionic variety. Typical cationic (acidic) catalysts in this case are Lewis acids. Yields and proportions of the various species are generally very similar to those obtained in anionic polymerizations, although the mechanism is very different. The reaction is thought to proceed through a tertiary oxonium ion formed by addition of a proton to one of the O atoms of the cyclic siloxane. Part of the mechanism may involve step growth, as well as the expected chain growth. 

Polarity of Environment. A strongly hydrophobic environment inhibits solvation and hence stabilization of the ionic conjugate bases in (II) and (III). Ionization is thus suppressed in these cases, and the pKa values increase. On the other hand, the pA"a of the cationic acid (I) is expected to decrease, hence the cationic acid becomes more acidic, since the resulting conjugate base is uncharged. 

The formation constants K,(B11B ) for the hydrogen bonding of cationic acids, BH+ with free N-bases (B). 

Arenes spontaneously form intermolecular 1 1 complexes with a wide variety of electrophiles, cations, acids, and oxidants that are all sufficiently electron-poor to be classified as electron acceptors. Spectral, structural, and thermodynamic properties of these donor/ acceptor associates are described within the context of the Mulliken charge-transfer (CT) formulation. The quantitative analyses of such CT complexes provide the mechanistic basis for understanding arene reactivity in different thermal and photochemical processes. 

The association constants of the above salts are the highest in nitromethane (low DN), lower in acetonitrile (medium DN), and negligible in DMF (high DN). These results are well understood in light of the meaning of the donor number, as they reflect the ability of a solvent to interact with cations, acids, and other... 

Use mechanisms to show how monomers polymerize under acidic, basic, or free-radical conditions. For chain-growth polymerization, determine whether the reactive end is more stable as a cation (acidic conditions), anion (basic conditions), or free radical (radical initiator). For step-growth polymerization, consider the mechanism of the condensation. 

Therefore, if the group (such as the amino group) has a cationic acid form, a represents the fractional positive charge ... 

The neutral conjugate base, B is more soluble in organic solvents than the cationic acid HB+... 

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