Most students taking organic chemistry course must be quite familiar with the concept of acid-base chemistry. I expect that you already understand the very basic general chemistry knowledge of acid-base, so we won’t be going into too much detail about it. This series of posts aims to cover acid-base theory in organic chemistry, particularly on how they are extremely useful and widely applied in this interesting branch of chemistry.
Here are the topics we will cover in this series of posts.
Here we start with the basics to refresh your memory about the important concepts in acid-base chemistry, such as the three main acid-base theories and the concept of conjugate pair. We use organic compounds as examples so that you can directly see how certain organic compounds behave as acids or bases.
Here we will talk about the concept of acidity, basicity, and pKa. The fun starts when we learn how organic chemists commonly see bases through its conjugate acid. This is where I introduce to you the concept of pKaH. This fundamental topic is very crucial for understanding the application of acid base concepts in organic chemistry. Most of the later topics we talk about in the acid-base series of posts are related to the usage of pKa and pKaH. They will also be used in many other non acid-base topics, so you should have a firm grasp of the concept of pKa in organic chemistry.
Chemistry is all about structures. So in these posts, we talk about how differences in structures influence the acidity of organic compounds. We start by listing common functional groups with their respective pKa values, known as the pKa table. Then, we start talking about the difference in acidity amongst functional groups, by talking about the difference in structures and factors influencing it, and using the pKa values to justify the theory.
Acid-Base V. Using pKa to Predict the Course of a Reaction – Part 1
Acid-Base VI. Using pKa to Predict the Course of a Reaction – Part 2
Acid-Base VII. Using pKa to Predict the Course of a Reaction – Part 3
This series of posts is where the real application of pKa in organic chemistry is discussed. Here we talk about how to predict the course of reactions using the pKa values of the species involved in the reactions. We also see why certain groups are good leaving groups and others aren’t; and why sometimes those we consider bad leaving groups are able to become one. These two posts cover the most important applications of acid-base in organic chemistry.
Both of these posts discuss the difference in acidity and basicity of species in different solvent. They also prepare you for the next important bit of theory in acid-base: the levelling effect.
The levelling effect concept helps us in choosing the right solvent for a reaction by looking at its acid-base related role in that particular reaction. Quite a lot of students find it hard to grasp the concept of levelling effect, but it is a very important concept and it has a practical application.
The Hard and Soft Acids and Bases (HSAB) theory is an important theory that has an application in conjugate addition reaction. The addition of nucleophiles to α,β-unsaturated carbonyl compounds may result in a nucleophilic addition at the carbonyl carbon, or in a conjugate addition at the β-carbon. The HSAB theory explains this phenomenon from the point of view of the nucleophiles and electrophiles.
Page last updated: 10iii17
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