Confused About Hydroxy Butanoic Acids and Amide Hydrolysis: Can Someone Explain?

In summary, the book explains that we can distinguish between 2 hydroxy butanoic acid (A) and 3 hydroxy butanoic acid (B) by haloform tests, with B giving a positive test due to the presence of a methyl group adjacent to the hydroxyl group. However, A does not give a positive test because there is no such methyl group present. In terms of base-catalyzed hydrolysis of amides and Hoffmann degradation, the OH- ion can act differently in each case due to the presence of a methyl group or lack thereof. This can result in different products being formed, depending on whether nucleophilic addition or deprotonation occurs. Overall, the use of OH-
  • #1
zorro
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1) My book says that we can distinguish between 2 hydroxy butanoic acid (A) and 3 hydroxy butanoic acid (B) by haloform tests. It says that B gives positive haloform test. I am fine with it.
I don't get why A doesnot give positive test as it is also a sec. alcohol .

2)In the base-catalysed hydrolysis of amides, they undergo nucleophilic addition of OH- and finally form acetate.
In hoffmann degradation, we use OH- (of an alkali) where it extracts a proton from the -NH2 group and does not add to the amide.

Why is the action of same OH- different in two cases?

Any help appreciated.
 
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  • #2
1) Regarding the first question: the haloform reaction requires a methyl group to be adjacent to a carbonyl or a secondary alcohol that can be oxidized to a carbonyl. So in alpha-hydroxy butanoic acid, there is no methyl group adjacent to the hydroxyl group. In beta-hydroxy butanoic acid, C-4 is adjacent to the hydroxyl group.

2) I'm speculating a bit here: it sounds like one is the kinetic product (nucleophilic addition) and the other is the thermodynamic product (deprotonation of the amide). I imagine that in practice, the reaction conditions would be tailored to favor one over the other, but that both *could* happen depending on how the hydroxide ion attacks the amide. This is the case with many reactions and is one way that product yields are lowered (competing reactions).
 
  • #3
Thanks DDTea!
 

1. What is the difference between a structural isomer and a stereoisomer?

A structural isomer is a molecule with the same chemical formula but different connectivity of atoms. A stereoisomer, on the other hand, has the same connectivity of atoms but differs in their spatial arrangement. In other words, structural isomers have different arrangements of atoms while stereoisomers have different arrangements of groups around a central atom.

2. How do I determine the number of stereoisomers in a molecule?

The number of stereoisomers in a molecule can be determined by using the concept of chirality. If a molecule has a chiral center (an atom with four different substituents), it can exist in two different enantiomeric forms. The number of stereoisomers can be calculated using the formula 2^n, where n is the number of chiral centers in the molecule.

3. What is the concept of resonance in organic chemistry?

Resonance is a concept used to describe the delocalization of electrons in a molecule. It occurs when a molecule can be represented by two or more Lewis structures that differ only in the placement of electrons. The actual electronic structure of the molecule is a hybrid of all the possible resonance structures.

4. How do I determine the acidity or basicity of a compound?

The acidity or basicity of a compound can be determined by looking at its functional groups. Compounds with a carboxylic acid functional group (COOH) are acidic, while compounds with an amine functional group (NH2) are basic. The presence of electronegative atoms, such as oxygen or halogens, also increases the acidity of a compound.

5. How can I improve my understanding of organic chemistry reactions?

To improve your understanding of organic chemistry reactions, it is important to practice regularly and understand the underlying principles and mechanisms. Additionally, reviewing and understanding the effects of functional groups, reagents, and reaction conditions can also help in understanding the outcome of a reaction. It can also be helpful to use visual aids, such as reaction mechanisms and diagrams, to better understand the steps involved in a reaction.

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