P/C, values for

Chemical Structures, CAS Number, and Experimental log P c, Values for the Set of 91 Rigid Molecules... 

Note that the p/C, of a residue at the active site can vary substantially from the value observed for the free amino add in water [27]. For example, the active site of the enzyme acetoacetate decarboxylase features a lysine residue with a very low p/C, of 5.9 (cf. pJCa 9 for the free amino add). In this case, the pICa is influenced by an adjacent protonated lysine residue (Figure 5.6) [28,29]. A similar redudion, though less dramatic, is observed for aliphatic diamines (e.g., the two p/C, values for 1,4-diaminobutane are 10.80 and 9.35, respectively). 

Ground and Excited-state p/C -Values for Substituted 2-Nitroanilinesa... 

Table 111.11 Seleciivit>-, permeability, and P/C values for various concerts...

Because of the analogy with ammonia, you should feel comfortable with the idea of amines as bases. The p/C value for a protonated amine, [RjNHjh is about 9, so it is a stronger acid than water, but not as strong as HjOh However, amines may also act as acids and can be deprotonated. For a typical secondary amine, the p/C is 36 (Equation 4.1). We will explore in more detail the acidity and basicity of all classes of compounds in Chapter 8. 

Hydrogen cyanide and alkane thiols have p/C values in the 9to 10 range and the p/C for acetylene is 26... 

Note that in Ref. 55 the "c values for the P-bound and N-bound water molecules were eiToneously interchanged. Source Ref. 55. 

C18-0142. The amine group of an amino acid readily accepts a proton, and the protonated form of an amino acid can be viewed as a diprotic acid. The p Zg values for serine (H2 NCHRCO2 H, i = CH2 OH) are p ra(H3 N"") =9.1 and p (002 H) - 2.2. (a) What is the chemical formula of the species that forms when serine dissolves in pure water (b) If this species is titrated with strong acid, what reaction occurs (c) 10.00 mL of 1.00 M HCl is added to 200. mL of 0.0500 M serine solution. This mixture is then titrated with 0.500 M NaOH. Draw the titration curve, indicating the pH at various stages of this titration. 

Figure 29 shows the P,C correlation for compound 1 carried out by selecting a J value of 15 Hz. The decoupled phosphorus signal is shown at the top, the proton decoupled carbon-13 spectrum on the left. The actual 2D spectrum... 

The fact that reaction can be made to go with (25), but not with the simple R OH, is due to the ASe (c/ p. 36) value for the former being more favourable than that for the latter, which involves a decrease in the number of molecules on going from starting material to product. Both aldehydes and ketones that are otherwise difficult to convert into acetals may often be transformed by use of orthoesters, e.g. HC(OEt)3, triethoxymethane ( ethyl orthoformate ), with NH Cl as catalyst. 

Calculations have been carried out by Edsall and Wyman (1958) for dioxane-water solutions (v/v 70 30), the dielectric constant of which is 18. The increase in the pi a between this medium and water should correspond to 5.3 units at 25 C. The observed p/Ca values for acetic acid are 4.756 in water and 8.321 in the above medium, that is, a difference in p Ca of 3.565. 

The viscosity behavior described so far is valid only for uncharged polymers. If polyelectrolytes are analyzed, a quite different viscosity behavior may be found in polar solvents (e.g., polymeric acids in water). The q p/c values at first fall off with decreasing concentration as for uncharged polymers but then climb steeply again and may drop down later again (see Fig. 2.16). Addition of salt to the solution of polyelectrolytes (e.g., 1% and 5% sodium chloride in aqueous solution) restores, step by step, the normal behavior (see Fig. 2.16, curves b and c). 

P jjj has already validated the predictions to some extent. A very large P value (e.g., unknown 2 on class A has a calc of 11,000) indicates a very large difference ijetween the unknown sample and the calibration samples from that class. Unknown 1 has large P j values for all of the classes with most of the conisSbution coming from the PCA measurement residual. Unknown 2 is within the box of all SIMCA models but has large PCA contributions with classes A and C. Unknown 3 is excluded only from class C primarily because of a large contribution from the distance term (the expected value is zero). 

Now we consider the solvent effects on the mutual relationship between the p/C, values of different adds. Figure 3.2 shows the relations between pfC, of non-ortho-substituted phenols and the Hammett er-values of the substituents [8]. Good linear relations are observed in four solvents.3 It is of special interest that the slopes in AN, DMF and DMSO are almost the same and are nearly 2.0 times the slope in water. Similar linear relations have also been obtained for non-ortho-sub-... 

The diagnostic coupling constant /P c for conformational analysis of phosphorinanes (P-CN = 3) is lost with phosphorinanes where P-CN = 4. Shifts and /P c values of two non-rigid and two cis-trans rigid phosphorinane 1-oxides and 1-sulfides should be studied for comparison (Tables 2 and 3). The large differences between the two classes are then evident. 

The p-Ka values for the NH acid dissociation of pyrrole and its benzo derivatives are closely similar. Recent measurements conducted in DMSO set the values at 19.90, 20.95 and 23.05 for carbazole, indole and pyrrole, respectively (81JOC632), although pKa values as low as 17.5 for pyrrole and 16.97 for indole have been recorded (67T2855). No reliable values are available for the NH dissociation of isoindole, as such measurements are complicated by the tautomeric equilibrium between the 1H and 2H isomers. It is apparent that many of the reactions conducted under strongly alkaline conditions and described in other sections could well proceed on the heterocyclic anions. In this section the discussion is centred upon reactions in which the C or N anionic species of the heterocycles are specifically produced. 

The p.Ka values for certain pyrimido[4,5-c]pyridazines have been determined (58LA(615)48). Mass spectral fragmentations for several derivatives of this ring system have also been reported (82JOC674), as well as Hiickel MO calculations (66JSP(19)25). 

Tabulating absorption coefficients c (p,T) for a range of (p,T) values for each absorber g... 

Table 13 Rate Constants and p K, Values for the Base Hydrolysis of some Copper(II) Complexes of Dipeptide Esters at 25 °C and I -0.01 Ma...

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