Amide Functional Group
A compound with the general formula RC(=O)NR′R′′, where R, R', and R′′ represent organic groups or hydrogen atoms, is known as an amide, also known as an organic amide or a carboxamide in organic chemistry. When it appears in the main chain of a protein, the amide group is called a peptide bond, and when it occurs in a side chain, such as in the amino acids asparagine and glutamine, it is called an isopeptide bond. It can be thought of as a carboxylic acid derivative RC(=O)OH with the hydroxyl group –OH substituted by an amine group –NR′R′′, or as an acyl (alkanoyl) group RC(=O)– joined to an amine group. In this article, we will study amide functional group, amide general structure, functional groups amide and monocarboxylic acid amide in detail.
Primary, secondary, and tertiary amines are graded according to whether the amine subgroup has the form –NH2, –NHR, or –NRR', where R and R' are non-hydrogen groups Given below is the amide group structure for primary, secondary and tertiary amide.
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Common Amides
Amides can be found in both nature and technology. Proteins and essential plastics such as Nylons, Aramid, and Kevlar are polymers with amide groups (polyamides) linking their units; these linkages are easy to shape, provide structural rigidity, and resist hydrolysis. Many other essential biological molecules, as well as medications such as paracetamol, penicillin, and LSD, are amides. Solvents with low molecular weight, such as dimethylformamide, are commonly used.
Amide and Amine
The addition of a carbonyl group to an amine has two important effects on the nitrogen's properties.
For instance, amide nitrogen is much less basic than amine nitrogen. This is largely due to the delocalization of the nitrogen lone pair into the carbonyl's pi bond. Oxygen, not nitrogen, is the most fundamental position of an amide.
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Second, amide N–H bonds are slightly more acidic than amine N–H bonds. Because delocalization occurs. The conjugate base's lone pair can be delocalized by resonance to the attached carbonyl group. Acetamide has a pKa that is about 20 orders of magnitude higher than ammonia.
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Amide Solubility
The carbonyl (C=O) is a stronger dipole than the N–C dipole due to oxygen's higher
electronegativity. Amides will behave as H-bond acceptors because they have a C=O dipole and, to a lesser degree, an N–C dipole. The presence of N–H dipoles in primary and secondary amides enables them to act as H-bond donors. As a result, amides can hydrogen bond with water and other protic solvents; the oxygen atom can accept hydrogen bonds from water, while the N–H hydrogen atoms can donate hydrogen bonds. As a result of interactions like these, amides have a higher water solubility than corresponding hydrocarbons. These hydrogen bonds play an important role in the secondary structure of the protein.
Synthesis of Amide
Nucleophilic Acyl Substitution of Acyl Halides (or Anhydrides) With Amines
With amine nucleophiles, acyl groups attached to a good leaving group, such as acid chlorides or acid anhydrides, can easily undergo nucleophilic acyl substitution.
If only the carboxylic acid is available, converting it to an acid chloride with a reagent like a thionyl chloride (SOCl2) is a successful first step in converting a carboxylic acid to an amide.
Treating a carboxylic acid with an acyl halide, on the other hand, produces an anhydride, which is also useful.
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Hydrolysis of Nitriles
Nitriles are hydrolyzed to primary amides under acidic or basic conditions
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By reacting amines with a carboxylic acid in the presence of the dehydrating agent.
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Did You Know?
Amino acids are organic molecules that have three functional groups: an amine (–NH2), a carboxylic acid (–COOH), and a side chain (that is specific to each amino acid). Proteins are made up of the same 20 amino acids in most living organisms. The carboxylic acid group of one amino acid reacts with the amine group of the other amino acid to create a peptide bond, which is a covalent bond formed when the carboxylic acid group of one amino acid reacts with the amine group of the other amino acid. A molecule of water is generated as a result of the forming of the bond (in general, reactions that result in the production of water when two other molecules combine are referred to as condensation reactions). A peptide bond is a type of amide bond. A peptide connection or peptide bond is the product of the carbonyl group carbon atom bonding with the amine nitrogen atom. More peptide bonds may form to other amino acids, expanding the structure, since each of the original amino acids has an unreacted group (one has an unreacted amine and the other has an unreacted carboxylic acid). A polypeptide is a sequence of associated amino acids. At least one long polypeptide chain can be found in a protein.
FAQs on Amide Group
1. What is an amide functional group and what is its general formula?
An amide is an organic compound containing a functional group called the amide group (or carboxamide group). This group consists of a carbonyl group (C=O) directly bonded to a nitrogen atom. The general formula for an amide is R-C(=O)N(R')R", where R, R', and R" can be hydrogen atoms or organic groups like alkyl or aryl groups.
2. What is the main difference between an amide and an amine?
The key difference lies in the presence of a carbonyl group. Amides have a carbonyl group (C=O) attached to the nitrogen atom, giving them the structure R-CO-NR'R". In contrast, amines are organic derivatives of ammonia where the nitrogen atom is bonded only to hydrogen atoms or alkyl/aryl groups, but not to a carbonyl group (e.g., R-NH₂).
3. How are amides classified? Provide examples.
Amides are classified into three types based on the number of hydrogen atoms attached to the nitrogen atom of the amide group:
- Primary (1°) Amides: The nitrogen atom is bonded to two hydrogen atoms (-CONH₂). Example: Acetamide (CH₃CONH₂).
- Secondary (2°) Amides: The nitrogen atom is bonded to one hydrogen atom and one alkyl/aryl group (-CONHR'). Example: N-methylacetamide (CH₃CONHCH₃).
- Tertiary (3°) Amides: The nitrogen atom is bonded to two alkyl/aryl groups and no hydrogen atoms (-CONR'R"). Example: N,N-dimethylacetamide (CH₃CON(CH₃)₂).
4. What are some important examples of amides found in nature and industry?
Amides are crucial in both biological systems and industrial applications. In nature, the most prominent example is the peptide bond, which is an amide linkage that connects amino acids to form proteins. Industrially, amides form the backbone of important polymers known as polyamides, such as Nylon and Kevlar, valued for their strength and durability. Many pharmaceuticals, like paracetamol, are also amides.
5. Why are amides significantly less basic than amines?
Amides are much weaker bases than amines due to the electronic effect of the adjacent carbonyl group. The lone pair of electrons on the nitrogen atom is not fully available to accept a proton because it is delocalised through resonance with the electronegative oxygen atom of the carbonyl group. This electron-withdrawing effect reduces the electron density on the nitrogen, making it less basic.
6. How does the amide group's structure allow it to participate in hydrogen bonding?
The amide group is excellent at forming hydrogen bonds. The oxygen atom of the carbonyl group (C=O) has a partial negative charge and can act as a hydrogen bond acceptor. In primary and secondary amides, the hydrogen atoms attached to the nitrogen (N-H) have a partial positive charge and can act as hydrogen bond donors. This ability is fundamental to the secondary structure (alpha-helices and beta-sheets) of proteins.
7. What is the role of the amide group in the structure of proteins?
In proteins, the amide group forms a special covalent bond known as a peptide bond. This bond is formed when the carboxylic acid group of one amino acid reacts with the amine group of another. The resulting chain of amino acids, linked by these peptide bonds, is called a polypeptide. The rigidity and planar nature of the peptide bond are critical for defining the stable three-dimensional structures of proteins, which determines their biological function.
8. What are two common methods for preparing amides as per the NCERT syllabus?
According to the CBSE/NCERT curriculum for the 2025-26 session, two key methods for amide preparation are:
- From Acyl Halides or Anhydrides: Amides are formed by the nucleophilic acyl substitution reaction of ammonia or an amine with an acyl chloride or acid anhydride. This is a very common and efficient laboratory method.
- Partial Hydrolysis of Nitriles: Nitriles (R-C≡N) can be hydrolysed under controlled acidic or basic conditions to yield primary amides. If the reaction is allowed to proceed further, the amide will hydrolyse into a carboxylic acid.
