P/C values

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

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

Practically, the q p/c values are plotted against the concentration, c, and linear extrapolation is done, [q] is obtained as they-axis intersect. 

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). 

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-... 

Proton transfers between oxygen and nitrogen acids and bases are usually extremely fast.72 In the thermodynamically favored direction they are generally diffusion controlled.71 In fact, a normal acid is defined74 as one whose proton transfer reactions are completely diffusion controlled, except when the conjugate acid of the base to which the proton is transferred has a p/C value very close (differs by < about 2 pK units) to that of the acid. The normal acid-base reaction mechanism consists of three steps ... 

Harris, T.K. Turner, G.J. (2002) Structural basis of perturbed p/C, values of catalytic groups in enzyme active sites. IUBMB Life 53, 85-98. 

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. 

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 4-3 in Chapter 4 lists some commonly used buffers for reversed-phase HPLC. In this table the buffers and their respective p/C values, and UV cutoffs are listed. Since it is becoming more common to find HPLC interfaced to mass spectrometers, volatile buffers for LC/MS applications are also indicated. 

The physicochemical approach to retention time prediction has the advantage of accounting for the pH of the system by explicitly calculating p/C values... 

Let us suggest that for compounds in ES we have values of some targeted molecular property. Expert divides ES into two parts positive and negative examples. Using a constructed estimator we calculate P(C) values and, selecting the threshold value, divide ES into two other parts predicted positive... 

R = Me) (see Scheme 27) were found to have p C values of 2.5 and 2.3, respectively. They are about four powers of ten weaker bases than the similarly substituted pyridines (170) and (171), which have p/Ca values 6.5 and 6.3, respectively (71ACS2435). 

Near 300 nm a spectral shift of 30 nm corresponds approximately to a change in wave number of Ai> = 3,300 cm". From Equation (1.53) this results in a p/C value change of 7 units. Since shifts of this extent are quite common on protonation, changes in dissociation constants of protonated compounds by 6-10 orders of magnitude on excitation are often observed. 

Box 3.9 Chemical structures and p(C values of some zwitterionic drugs... 

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