Conjugate bases relative stability

Loss of a proton is relatively rare but may take place in cases where there is a positive charge on the complex (e.g. IrH2(diene)L in equation 8) or the anionic conjugate base is stabilized (e.g. HCo(CO)4 in equation 9). 

The bottom portion of Table 8.1 consists of very weak acids pK. above 17). In most of these acids, the proton is lost from a carbon atom, and such acids are known as carbon acids. The pa s values for such weak acids are often difficult to measure and are known only approximately. The methods used to determine the relative positions of these acids are discussed in Chapter 5. The acidity of carbon acids is proportional to the stability of the carbanions that are their conjugate bases (see p. 227). 

The classification into Kekule and non-Kekule diradicals is mainly based on the difference in their resonance structures. From the proceeding discussions, however, such a classification does not closely relate to the relative stabilities and spin preference of TT-conjugated diradicals. For example, some non-Kekule diradicals, such as 1 and 8, prefer a triplet ground state, but some others (like 7) have a singlet ground... 

The electronegativity of this atom affects the polarity of the bond to the proton, and it affects the relative stability of the anion (conjugate base). 

Alder reactions to give the endo adduct as in (18) ->(19) rather than the exo one as in (18) ->(20)] in terms of qualitative perturbation theory. Similar methods were used by Hoffmann and his co-workers in discussion of favourable and unfavourable conformations of conjugated systems,93 and of relative stabilities of isomers.94 All these treatments are based, implicitly or explicitly, on extended Huckel theory,... 

Likewise, carbonic acid CO(OH)2 is rather unstable with respect to C02 and water since the very strong bonds in COz are resistant to addition. But the CO3- and HCOf ions are stabilised by resonance. The relative strengths of oxoacids in aqueous solution are evidently dependent on the stabilities of their conjugate bases, in which resonance (electron de-localisation) appears to play some part. 

The varying acidic strengths of ethanoic acid, phenol and ethanol can be explained by considering the relative stabilities of their conjugate bases ... 

Buffers stabilize a solution at a certain pH. This depends on the nature of the buffer and its concentration. For example, the carbonic acid-bicarbonate system has a pH of 6.37 when the two ingredients are at equimolar concentration. A change in the concentration of the carbonic acid relative to its conjugate base can shift the pH of the buffer. The Henderson-Hasselbalch equation below gives the relationship between pH and concentration. 

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