Conjugate acids of amines

P Chemical Shifts of (HI) and pKa Values of the Conjugate Acids of Amines... 

For dissociation of conjugate acid of amines. k Robinson and Stokes 46). 

Explain the observed difference in the pKg values of the conjugate acids of amines A and B. 

In the amine, the electron pair is mainly localized on the nitrogen. In the amide, the electron pair is delocalized to the carbonyl oxygen. The effect of this delocalization is seen in the low pKa values for the conjugate acids of amides, compared with those for the conjugate acids of amines, for example ... 

Solvents appear as important players in questions of stability. For example, both the conjugate bases of alcohols (alkoxides) and the conjugate acids of amines (ammonium ions) depend greatly on solvation for stabilization. In assessing basicity or acidity, one must take account of the solvent. 

Aromatic amines are usually weaker bases than aliphatic amines as illustrated by the difference ia p of the conjugate acids of aniline (1), pK = 4.63 and cyclohexylamine (2), pif = 10.66. 

In these papers, the carboxylic acid to be protected was a stable, unsubstituted compound. Harsh conditions were acceptable for both formation and cleavage of the amide. Typically, a simple secondary amide is very difficult to cleave. As the pKa of the conjugate acid of an amide decreases, the rate of hydrolysis of amides derived from these amines increases. The dimethylamide of a cephalosporin was prepared as follows using 2,2 -dipyridyl disulfide. ... 

Sometimes the acidity constant (acidity dissociation constant, KJ is employed for the conjugate acid of the amine used. Under these circumstances ... 

An intramolecular rearrangement of the conjugate acid of the triazene compound to form the oc-complex without an additional molecule of amine would correspond to a thermal [l,3]-sigmatropic rearrangement. However, such a mechanism can be ruled out on the grounds of the antarafacial pathway required from orbital symmetry considerations (Woodward-Hoffmann rules). 

On studying a series of ammonium 1,3,2,5-dioxaborataphosphorinane oxides (111), the dependence of the tautomeric equilibrium position on amine basicity was analyzed. The equilibrium position was estimated from chemical shift values of bis(oxymethyl)phenylphosphine oxide with 8 3IP of 35 ppm being used as a model of an acyclic form and 5-Ph-5-oxo-1,3,5-dioxaphosphorinane (107, R = H) with 8 3IP of 6 ppm used as a model of a cyclic compound. The chemical shift values (111, X = 0, R = H) and dissociation constants (pKa) of conjugate acids for amines are presented in Table V. 

One method is to treat 4-aminophenol with just one molar equivalent of acetic anhydride. The main product is paracetamol, which is produced almost selectively since -NH2 is a better nucleophile than -OH. We can predict this from their pATa values as bases, about 5 for the conjugate acid of a typical aromatic amine, and about —7 for a phenol, i.e. the amine is the stronger base. Although the heteroatoms are not the same (see Section 6.1.2), the pATa values are significantly different and allow us to predict that the amine is also going to be the better nucleophile. The higher the pAfa of the conjugate acid, the better the nucleophile. 

There is no way we would encourage the memorising of pATa values, but two easily remembered figures can be valuable for comparisons. Conjugate acids of typical aliphatic amines have pATa values around 10, whereas for pyridine the figure is around 5. These then allow us to consider whether the compound in question is more or less basic, etc. The smaller the pAfa, the weaker the base. Remember, of course, that the pATa values refer to the acidity of the conjugate acids, and not to the acidity of the amines themselves, which could be relevant in different circumstances. Nevertheless, it is usually acceptable to talk of the pAfa of the base, when we should strictly say the pAfa of the conjugate acid of the base. 

A study on the conjugate acids of dihydro-6//-dibenz[c,e]azepines has demonstrated the validity of the Karplus equation for determining H—N—C—H coupling constants in secondary and tertiary amines of known rigid conformation (73CJC2433). 

The dicarbonyl [12539-66-1] available from 1,10-(N2)2B10H8 is another important species because of the scope ofits chemistry. Carbonyls of P 12 -12] can be formed from CO and the conjugate acid of [B12H12]2 . The B10- and B12-carbonyls exhibit very similar reactivity (99). The carbonyls can be considered anhydrides of carboxylic acids and accordingly react with alcohols and amines-to give esters and amides ... 

Certain octahedral complexes, particularly the acido—amine complexes of cobalt(III), undergo substitution in protonic solvents at rates that are proportional to the concentration of the conjugate base of the solvent (e.g. OH- in water) or inversely proportional to the concentration of the conjugate acid of the solvent (e.g. retardation by H30+ in water or NH4+ in liquid ammonia). Such reactions have received considerable attention since systematic studies of ligand substitution commenced, and figured amongst the earliest kinetic studies in the field.298 The subject has been... 

Figure 2.5 The Br0nsted plot for the general-base catalysis of the hydrolysis of ethyl dichloroacetate. The logarithms of the second-order constants obtained from the plot of Figure 2.4 are plotted against the pAT s of the conjugate acid of the catalytic base. The slope is the /3 value. Note that the points for amine bases ( ) fall on the same line as those for oxyanion bases (O), showing that the catalysis depends primarily on the basic strength of the base and not on its chemical nature.

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