Carbon-hydrogen acids, dissociation constants

If a methyl group replaces a hydrogen atom on the carbon of the C==N bond across which addition of water occurs, a considerable reduction in the extent of water addition is observed. Conversely, the existence of such a blocking effect can be used as a provisional indication of the site at which addition of water occurs, while the spectrum and acid dissociation constant of the methyl derivative provide a useful indication of the corresponding properties of the anhydrous parent substance. Examples of the effect of such a methyl group on equilibria are given in Table IV. 

The fluorotelomer carboxylic acids (FTCAs) and fluorotelomer unsaturated carboxylic acids (FTUCAs) are degradation products of FTOHs with the general structure F(CF2) CH2CH00H and F(CF2) CHCOOH respectively, where usually n = 6, 8 or 10 (Table 3.1). Similar to FTOHs, FTCAs and FTUCAs are also named based on the ratio of fluorinated carbons to hydrogenated carbons in the molecule. Although the acid dissociation constants are not known for the FTCAs and the FTUCAs, it is assumed they will also dissociate in the natural environment ... 

The C—H acid dissociation constant. A, is related to the hybridization of the carbon atom. It increases for carbon atoms in the order sp < sp < sp. This order of acidities parallels the percent s character of the hybrid orbitals. Because an sp hybrid orbital has more s character than an sp or sp5 orbital, its electrons are located closer to the nucleus, and a hydrogen atom bonded to an sp-hybridized carbon atom can be more easily removed as a proton. 

The amount of carbonic acid present, undissociated or dissociated, is only about 1 of the total concentration of dissolved carbon dioxide. Carbonic acid, in l especi of its dissociation into hydrogen and hydrogencarbonate ions, is actually a stronger acid than acetic acid the dissociation constant is ... 

The physical properties of cyanoacetic acid [372-09-8] and two of its ester derivatives are Hsted ia Table 11 (82). The parent acid is a strong organic acid with a dissociation constant at 25°C of 3.36 x 10. It is prepared by the reaction of chloroacetic acid with sodium cyanide. It is hygroscopic and highly soluble ia alcohols and diethyl ether but iasoluble ia both aromatic and aUphatic hydrocarbons. It undergoes typical nitrile and acid reactions but the presence of the nitrile and the carboxyUc acid on the same carbon cause the hydrogens on C-2 to be readily replaced. The resulting malonic acid derivative decarboxylates to a substituted acrylonitrile ... 

Explain why the equality of the hydrogen ion and hydroxyl ion concentrations is violated when certain salts are dissolved in water. Compare the values of the dissociation constants of water, acetic acid, carbonic acid, the bicarbonate ion, and aluminium hydroxide. How can the hydrolysis process be explained from the viewpoint of the law of mass action In what cases is hydrolysis reversible and in what cases does it proceed virtually to the end ... 

The coefficients in equations (26) and (27) for the dissociation of a number of acids and the solubility of calcium carbonate are given in Table A6.5 (Millero, 1979, 1995). The results for carbonic and boric acid are taken from the measurements of Culberson and Pytkowicz (1968). The effect of pressure on the solubility of calcite and aragonite has been determined from the measurements of Ingle (1975). The effect of pressure on the dissociation constants of water, hydrogen sulfate, hydrogen sulfide, ammonia, and hydroffuoric and phosphoric acids have been estimated from molal volume and compressibility data. 

Note that in this case, only intermolecular hydrogen bonding is possible, because of the rigid nature of the central carbon/carbon double bond. The difference in the stability of the intermolecular versus the intramolecular hydrogen bond is reflected in the difference in the acidities of the first hydrogen to be removed in each case. The trans isomer has a dissociation constant of 3.02, while for the cis isomer it is 1.92, i.e. the latter is a stronger acid. 

The 5,8-dihydroxy-4(3//)-quinazolinones possess three protons capable of dissociation in aqueous buffer, viz. N3—H and the protons of the 5- and 8-hydroxyl groups (Scheme 107). Initial acid dissociation of the N3 proton does not take place at low pH because electron-rich substituted quinazolin-4(3//)-ones possess pK values greater than 10. The first dissociation is from the 5-hydroxyl which affords an anion (697) which is stabilized by internal hydrogen bonding expressed by pK 7.3 (7.8). Cleavage of the halogen-carbon bond in the 2-substituent in (697) involves a rate-determining reaction of the hydroquinone monoanion and dianion species, since there is an approximate 100-fold difference in rate constants between the precursor 2-chloro (696 X = Cl) and... 

As an illustration, Table I shows data for the base-catalyzed halogenation of a number of ketones and similar substances. In this table, R is the catalytic constant (in liters/mole/minute) of the anion of a hypothetical acid of dissociation constant 10-4 obtained by interpolating data for carboxylate anions. In computing R a statistical correction has been made for the number of equivalent hydrogen atoms in the substrate, counting as independent atoms attached to the same carbon. /3 is the exponent in Eq. (51). 

In clean natural water the pH can be calculated from the content of free CO2 and hydrogen carbonates using the expression for the first dissociation constant of carbonic acid. Dissociation to the 2nd degree can be neglected as its effect becomes significant only as pH > 8.3. Due to the inaccurate determination of free CO2 the calculation provides only rough results. On the contrary, from a known value of pH and the content of HCO3 the content of free CO2 can be calculated. 

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