Amido And Amide: Structure, Preparation, Classification, Different Types
Have you ever wondered how proteins in our body are linked together or what functional group is responsible for the peptide bond in amino acids? Why are compounds containing the –CONH₂ group called amides, and how are they different from amido compounds containing the –NH- ion? Understanding amides and amido compounds is important because they play vital roles in organic synthesis, biochemistry, pharmaceuticals, and industrial chemistry. In this article, we will study the structure of amide, the difference between amide and amido group, along with some solved examples
This Story also Contains
- Structure of Amide
- Difference Between Amide And Amido Group
- Preparation Of Amides
- Some Solved Examples
Structure of Amide
An amide is a carboxylic acid derivative in which the –OH group of a carboxylic acid is replaced by an amino group (–NH2), substituted amino group (–NHR), or disubstituted amino group (–NR2).
General Structure
Primary Amide: $\mathrm{R}-\mathrm{CONH}_2$
Secondary Amide: R-CONHR'
Tertiary Amide: R-CONR'R"
- The amide functional group consists of a carbonyl group (C=O) directly bonded to a nitrogen atom.
- Due to resonance, the lone pair of electrons on nitrogen is delocalized towards the carbonyl group.
- As a result, the C–N bond acquires partial double-bond character.
- The atoms involved in the amide group (O, C, N, and attached atoms) are generally coplanar.
- Rotation around the C–N bond is restricted because of its partial double-bond nature.
Difference Between Amide And Amido Group
There is not much difference between these two of the group The only difference that indicates is amido group indicates the presence of an amide group in it.
| Feature | Amide Group | Amido Group |
|---|---|---|
| Definition | A functional group derived from a carboxylic acid by replacing the –OH group with –NH₂, –NHR, or –NR₂. | A negatively charged nitrogen-containing group formed by the removal of a proton from ammonia or an amine. |
| General Formula | $-\mathrm{CONH}_2,-\mathrm{CONHR},-\mathrm{CONR}_2$ | –NH-, –NR- |
| Charge | Neutral | Negatively charged |
| Presence of Carbonyl Group (C=O) | Present | Absent |
| Nature | Covalent functional group | Anionic group |
| Basicity | Weakly basic due to resonance. | Strongly basic due to the negative charge on nitrogen. |
| Examples | Acetamide $\left(\mathrm{CH}_3 \mathrm{CONH}_2\right)$, Benzamide $\left(\mathrm{C}_6 \mathrm{H}_5 \mathrm{CONH}_2\right)$ | Sodium amide (NaNH₂), Lithium diisopropylamide (LDA) |
| Uses | Found in proteins, polymers, pharmaceuticals, and organic compounds. | Used as strong bases in organic synthesis and deprotonation reactions. |
Preparation Of Amides
Amides can be prepared by several methods. Some important methods are discussed below:
1. Acylation of Amines
Amides are commonly prepared by the reaction of an amine with a carboxylic acid derivative such as an acid chloride, acid anhydride, or ester. The nitrogen atom of the amine contains a lone pair of electrons, which attacks the electron-deficient carbonyl carbon of the carboxylic acid derivative. This leads to the formation of a new C–N bond, followed by the elimination of a leaving group to produce an amide.
$\mathrm{CH}_3 \mathrm{COCl}+\mathrm{NH}_3 \rightarrow \mathrm{CH}_3 \mathrm{CONH}_2+\mathrm{HCl}$
2. Hydrolysis of Nitriles
Amides can be obtained by the partial hydrolysis of nitriles (RCN) under acidic or basic conditions. During hydrolysis, the nitrile group first converts into an amide. On further hydrolysis, the amide may be converted into a carboxylic acid.
$\mathrm{RCN}+\mathrm{H}_2 \mathrm{O} \xrightarrow[\text { controlled conditions }]{\mathrm{H}^{+} \text {or } \mathrm{OH}^{-}} \mathrm{RCONH}_2$
3. Beckmann Rearrangement
The Beckmann rearrangement is one of the most important methods for the synthesis of amides. In this reaction, oximes undergo rearrangement in the presence of acidic dehydrating agents such as concentrated sulfuric acid (H₂SO₄), phosphorus pentachloride (PCl₅), or phosphorus oxychloride (POCl₃) to form amides.
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Some Solved Examples
Question 1: Which of the following compounds is an amide?
A. $\mathrm{CH}_3 \mathrm{NH}_2$
B. $\mathrm{CH}_3 \mathrm{CONH}_2$
C. $\mathrm{CH}_3 \mathrm{CN}$
D. $\mathrm{CH}_3 \mathrm{NO}_2$
Solution:
Amides contain the functional group $-\mathrm{CONH}_2,-\mathrm{CONHR}$, or $-\mathrm{CONR}_2 . \mathrm{CH}_3 \mathrm{CONH}_2$ (acetamide) contains the amide group.
Hence, the correct answer is option (B)
Question 2: The C–N bond in amides has partial double bond character due to:
A. Hyperconjugation
B. Inductive effect
C. Resonance
D. Hydrogen bonding
Solution:
The lone pair on nitrogen delocalizes into the carbonyl group.
$\mathrm{RCONH}_2 \leftrightarrow \mathrm{RC}\left(\mathrm{O}^{-}\right)=\mathrm{NH}_2^{+}$
Hence, the $\mathrm{C}-\mathrm{N}$ bond acquires partial double bond character.
Hence, the correct answer is option (C)
Question 3: Which of the following is the strongest base?
A. Aniline
B. Acetamide
C. Ammonia
D. Sodium amide (NaNH₂)
Solution:
$\mathrm{NaNH}_2$ contains the amido ion $\left(\mathbf{N H}_2{ }^{-}\right)$which carries a negative charge and is therefore an extremely strong base.
Hence, the correct answer is option (D)
Question 4: Acetamide on treatment with $\mathrm{LiAlH}_4$ gives:
A. $\mathrm{CH}_3 \mathrm{OH}$
B. $\mathrm{CH}_3 \mathrm{CHO}$
C. $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{NH}_2$
D. $\mathrm{CH}_3 \mathrm{COOH}$
Solution:
$\mathrm{LiAlH}_4$ reduces amides to amines.
$\mathrm{CH}_3 \mathrm{CONH}_2 \xrightarrow{\mathrm{LiAlH}_4} \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{NH}_2$
Hence, the correct answer is option (C)
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Frequently Asked Questions (FAQs)
Lactam amides are known as cyclic amides.
Hybridization is defined as the intermixing of atomic orbitals to form a hybrid orbital. Hybridization of amides is found out to be sp3. We can explain it as the electrons of three p orbitals are engaged on three atoms: oxygen, carbon and nitrogen and s orbital of hydrogen are on the same plane and delocalized.
Lower amides that are amides with lower number of carbon atoms are highly soluble in water as they are involved in hydrogen bonding with that of water. They act both as electron donor and electron acceptor as they have presence of both Nitrogen and oxygen.
When many amide groups are joined together by the help of covalent bonds these are termed as polyamides. They are present in a protein rich diet.
When the amides formed by the sharing of electrons are derived from the ammonia then they are solid except for the formamide which is a liquid kind amide. Amides that are derived from ammonia and those that contain less than 5 carbon numbers are usually soluble in water.
