Larger Kb values or smaller pKb values indicate stronger bases. The pKb value of ammonia is 4.75, and aliphatic amines, with a +I effect of alkyl groups, are stronger bases (pKb range: 3 to 4.22). Aromatic amines, with electron-withdrawing aryl groups, exhibit weaker basicity than ammonia.
How is the basicity of amines assessed using Kb and pKb values, and what is the significance of the pKb value of ammonia (4.75)?
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The basicity of amines is assessed using Kb (base dissociation constant) and pKb values. Kb quantifies the extent of ionization of an amine in water, with higher Kb values indicating stronger bases. The pKb value, the negative logarithm of Kb, provides a convenient scale for comparing basicities; lower pKb values correspond to stronger bases. The pKb value of ammonia (4.75) serves as a reference point. Amines with pKb values lower than ammonia are stronger bases, while those with higher values are weaker. It helps rank and compare the basicity of different amines in a standardized manner.