![]() This is interesting because oxygen is more electronegative than sulfur, and you’d expect the opposite acidity trend. If you look in the p Ka table, you will see that thiols (R-SH) are more acidic than alcohols: The acidity of H – A increases as the electronegativity of A increases going from left to the right in the periodic table: So, remember the first factor is the atom connected to the H, specifically the electronegativity of this atom. The answer is that it is more electronegative than the nitrogen – it likes electrons/negative charge or doesn’t mind them as much as nitrogen does. For example, we know that alcohols are more acidic than amines:Īnd this means the oxygen stabilizes the negative charge better than the nitrogen. ![]() The better it stabilizes the negative charge, the more stable the conjugate base is. Here, we are talking about the atom that is connected to the hydrogen. This is often abbreviated and referred to as ARIO or CARIO. There are four main factors, in the following priority order, that affect the stability of the conjugate base: Therefore, the explanation of the acidity relies on the stability of the conjugate base. For example,Īnd a weaker conjugate base means a more stable conjugate base because if it was not as stable as it is, it would have reacted with the proton and shift the reaction backward, forming the acid. The question is how do we explain these differences? Well, remember, we said that the stronger the acid, the weaker its conjugate base. ![]() The p Ka table shows how greatly the acidity varied for different functional groups. In the previous post, we talked about the acid strength and its quantitative description by p Ka. ![]()
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