Effects activity

Suppose you need to prepare a buffer with a pH of 9.36. Using the Henderson-Hasselbalch equation, you calculate the amounts of acetic acid and sodium acetate needed and prepare the buffer. When you measure the pH, however, you find that it is 9.25. If you have been careful in your calculations and measurements, what can account for the difference between the obtained and expected pHs In this section, we will examine an important limitation to our use of equilibrium constants and learn how this limitation can be corrected. 

Careful measurements of the solubility of AglOa show that it increases in the presence of KNO3, even though neither K+ or participates in the solubility reaction. Clearly the equilibrium position for the reaction 

A quantitative method for reporting the ionic composition of a solution that takes into account the greater effect of more highly charged ions (jr). 

The ionic composition of a solution frequently is expressed by its ionic strength, p, 

Calculate the ionic strength of 0.10 M NaCl. Repeat the calculation for a solution of 0.10 M Na2S04. 

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The same situation is observed in the series of alkyl-substituted derivatives. Electron-donating alkyl substituents induce an activating effect on the basicity and the nucleophilicity of the nitrogen lone pair that can be counterbalanced by a deactivating and decelerating effect resulting from the steric interaction of ortho substituents. This aspect of the reactivity of thiazole derivatives has been well investigated (198, 215, 446, 452-456) and is discussed in Chapter HI. 

The following experiments involve the experimental determination of equilibrium constants and, in some cases, demonstrate the importance of activity effects. 

Ignoring activity effects, calculate the solubility of Hg2Cl2 in the following... 

Repeat the calculations in problem 9, this time correcting for activity effects. 

Fillers. Materials used as fillers (qv) in mbber can also be classified as acidic, basic, or neutral. Furnace blacks, ie, HAF, FEF, or SRF, are somewhat basic. As such, they can have an activating effect on sulfur cure rates. Furthermore, carbon blacks have been found to promote formation of mono/disulfide cross-links thereby helping minimize reversion and enhance aging properties. 

A quantitative study has been made on the effect of a methyl group in the 2-position of five-membered heteroaromatic compounds on the reactivity of position 5 in the formylation and trifluoroacetylation reaction. The order of sensitivity to the activating effect of the substituent is furan > tellurophene >selenophene = thiophene (77AHC(2l)ll9). 

Alkoxy-2,l-benzisoxazole-4,7-diones undergo ready nucleophilic displacement of the 3-alkoxy substituent, yielding 3-alkylamino and 3-dialkylamino derivatives with primary and secondary amines, respectively (67TL4313). In this instance the 4-carbonyl group apparently provides an activating effect. 

We developed a sensor for determination of content of phosphorars in metallurgical melts. In quality of ion conductor used orthophosphate of calcium which pressed in tablets 010 mm. Tablets (mass 1-2 g) annealed at a temperature 400°C during 7-10 h. Tablets melts then in a quartz tube and placed the alloy of iron containing 1 mass % P. Control of sensor lead on Fe - P melts. Information on activities (effective concentration) of phosphorars in Fe - P melts was received. It is set that the isotherm of activity of phosphorars shows negative deviations from the Raouls law. Comparison them with reliable literary inforiuation showed that they agree between itself. Thus, reliable data on activities (effective concentration) of phosphorars in metallic melts it is possible to received by created electrochemical sensor for express determination. 

The reactivity of a series of hydrocarbons toward oxygen measured under a standard set of conditions can give some indication of the susceptibility of various structural units to autoxidation. Table 12.10 gives the results for a series of hydrocarbons. These data indicate the activating effect of alkyl, vinyl, and phenyl substituents. 

If the activating effect of a I + M-substituent (such as CH3, NHCOCH3, SCH3, or OCH3) were equal in the 3- and 5-positions, one would, of course, expect that substitution should occur in the 5-position because of the directing power of the sulfur. The experimental results show, however, that such substituents activate the 3-position much more than the 5-position. Thus the nitration of... 

It can be seen from resonance structures (2) to (4) that a — I — M-substituent deactivates the 3- and 5-position most strongly in electrophilic substitution. If this deactivation of the 5-position is strong enough to overcome the activating effects of the sulfur in the 5-position, substitution will be directed to the 4-position to an increasing extent. Tirouflet and Fournari studied the nitration of 2-substituted thiophenes of this type. The analysis was carried out polarographically, and the percentage of 4-isomer was as follows ... 

The AlCIs-catalyzed benzoylation of 2-methyl-5-phenyIthiophene to 2-methyl-3-benzoyl-5-phenylthiophene (118) is of certain interest for comparison of the activating effect of an alkyl and phenyl group. The structure of (118) was proved in an original way by conversion to (119) by an Elbs reaction. ... 

Competitive metalation of thiophene and 2-methylthiothiophene with a deficiency of n-butyllithium gave only 2-methylthio-5-thio-phenecarboxylic acid, showing the activating effect of the methylthio group. ... 

As to the electron-withdrawing substituents, the activating effect of a nitro group in the piperidino-dechlorination of 2-chloropyridine involves factors of 7.3 x 10 and 4.6 x 10 from the para and ortho positions, respectively. An ortho-cyano group was found to be... 

The A-oxidation of 3-chloropyridazines increases their reactivity toward methoxide and sulfanilamide anions.The reactivity of 4-chloro- or 4-nitro-quinoline and of chloropyridines toward methoxide ion and piperidine is less than that of the corresponding A-oxides (see Tables II and XI, pp. 270 and 338). The activating effect of the A-oxide moiety in 3-halopyridine A-oxides is greater than that of a nitro group, and in fluoroquinoline A-oxides the activation is transmitted to resonance-activated positions in the adjoining rings. 

The effect of a substituent may be substantially modified by fast, concurrent, reversible addition of the nucleophile to an electrophilic center in the substituent. Ortho- and para-CS.0 and pam-CN groups have been found by Miller and co-workers to have a much reduced activating effect on the displacement of halogen in 2-nitrohaloben-zenes with methoxide ion [reversible formation of hemiacetal (143) and imido ester anions (144)] than with azide ion (less interaction) or thiocyanate (little, if any, interaction). Formation of 0-acyl derivatives of 0x0 derivatives or of A-oxides, hydrogen bonding to these moieties, and ionization of substituents are other examples of reversible and often relatively complete modifications under reaction conditions. If the interaction is irreversible, such as hydrolysis of a... 

The activating effect of a trichloromethyl group is seen in the 2-dechlorination reactions of 2-chloro-4,6-bis(trichloromethyl)-s-tria-zine (175) with arylsulfonylhydrazides (24 hr) and heterocyclic amines (3 hr) at 20° and with unbasifled primary and secondary alcohols (65°, 30 min). The 4,6-diphenyl or 4,6-bis(4-chlorophenyl) analogs do not react in this manner. ... 

The activating effect of the phenylazo group in the reaction of 6-chloro-5-phenylazo-2,4-diaminopyrimidine and its analogs with amines or with dimethylformamide has been noted by Brown. The activating effect in 4-nitroso-, 4-phenylazoxy-, and 4-phenylazo-... 

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