Is Peptide Bond Covalent : How Why, Comparative Analysis and Facts

In this article, ”Is peptide bond covalent ” the covalent or the ionic character of peptide bond is discussed briefly.

Peptide bond, a very essential linkage in the primary structure of protein , is formed between two alpha amino acids and plays an important role construct protein, a macromolecule.  This formation of peptide bond is classified as condensation reaction because one water molecule (H2O) is eliminated from the reaction medium.

Some frequently asked questions about the covalency of the peptide bond are pointed out specifically in this article.

Is Peptide Bond Covalent

Peptide bond is a well known chemical covalent bond in chemistry.

Peptide bond links two amino acids, very specifically it can be described that peptide bond is the linkage between alpha amine group (NH2) and alpha carboxylic acid group (COOH) coming from two same or two different amino acid.

After elimination of water molecule peptide bond is formed and it is basically an amide (CONH2) type linkage between two consecutive alpha amino acid.

Peptide bond possesses a partial double bond character of C-N bond due to delocalisation of unshared pair of electrons coming from nitrogen into the carbonyl group (C=O). Thus peptide bond attains a planar geometry and sp2 hybridisation.

The above resonance structure and the explanation can describe that why peptide bond is a covalent bond.

To know more please check: Peptide bond formation: How, Why ,Where ,Exhaustive Facts around it

Are All Peptide Bonds Covalent?

 In Chemistry, all peptide bonds are amide type strong chemical covalent bond.

The main criteria to be fulfilled to form a covalent bond is sharing of valence electrons between the participating atoms. These electron pairs are called as bonding electron pairs. The driving force of the formation of covalent linkage is the electrostatic attraction of the participating nuclei for the electrons.

Peptide bonds generally bind the acid end of one alpha amino acid with the amino end of the next amino acid.

Peptide linkage is a strong covalent linkage that connects two amino acids and eliminates one water (H2O) molecule. One hydrogen atom from amine group (NH2) and OH from carboxylic acid group (COOH) is eliminated as water (H2O).

To know more please follow : Is HBr Ionic or Covalent : Why? How, Characteristics and Detailed Facts


Peptide Bond Covalent Characteristics

There are some characteristics of covalent peptide bond, described below-

Peptide bonds are strong, rigid and planar. Peptide bond is not flexible and free rotation about this bond is become restricted. This bond possesses some double bond character due to sharing of unpaired electrons, which is one of the main characteristics of covalent linkage.

Peptide bond also contains partial positive charge for the presence of polar hydrogen atoms of amino group and partial negative charge due to presence of polar oxygen atoms come from carboxylic acid group.

Due to the resonance stabilization, peptide bond basically remains unreactive under physiological conditions, even they are also less reactive with comparing to their almost similar compounds, ester.

To know more please check: Peptide Bond vs Ester Bond: Comparative Analysis And Facts

Why Peptide Bond is Covalent Bond?

The definition of ionic bond and covalent bond is discussed below-

Electrostatic attraction between the oppositely charged (positively charged and negatively charged) molecules is the main criteria to form an ionic bond. Thus it is called an electrovalent bond. In the formation of ionic bond, the valance electrons from the more electronegative atoms are permanently transferred to the more electropositive atoms.

Ionic compounds generally have higher and sharp melting and boiling point but peptides have melting point in the range between 250 to 1130 celcius. Thus peptides are not melted in a particular temperature.

From the above explanation it is clear that peptide bond does not execute any ionic compound character rather it shows covalent character like any other covalent compound.

To know more please follow: Peptide Bond vs Disulfide Bond: Comparative Analysis and Facts

Why Is Peptide Bond Not Ionic

There is a basic difference between the characteristics of covalent bond and an ionic bond.

The main difference between these two bonds is in their formation process. Permanent transfer of electrons between the atoms have to be fulfilled to form an ionic bond . whereas covalent bond is formed due to sharing of electrons between the atoms. The extent of sharing the electrons in covalent bond may not be equal and it depends upon the electronegative character of the atoms.

Ionic Bond Formation Through Permanent Transfer of Valence Electrons.
Image Credit: Wikimedia Commons

Covalent Bond Formation Due to Sharing of Valence Electrons.
Image Credit:

Peptide bond is formed due to sharing of electron pairs come from nitrogen to the carbon nitrogen bond known as peptide bond and achieves a partial double bond character and a rigid and planar structure.

Peptide bond gets extra stability due to this resonance and resonance stabilization cannot be achieved by any ionic bond. Resonance stabilization is an important stabilization factor of covalent bond.

All these discussion indicates that peptide bond is definitely a covalent bond, not an ionic bond.

Some frequently asked questions about the peptide bond is discussed below-

Frequently Asked Questions (FAQ)

How Peptide bond can be broken?

Answer: Peptide bond can be broken by hydrolysis. Amide type linkage is hydrolysed by adding of water and give two constituent amino acid residue.

Are Peptide bonds strong or weak?

Answer: Peptide bond is an example of strong covalent bond with a high bond dissociation energy.

Why peptide bond is covalent bond?

Answer: Peptide bond is formed due to sharing of electrons between carbon and nitrogen and this is one of the most important characteristics of an covalent bond.

Aditi Roy

Hello, I am Aditi Ray, a chemistry SME on this platform. I have completed graduation in Chemistry from the University of Calcutta and post graduation from Techno India University with a specialization in Inorganic Chemistry. I am very happy to be a part of the Lambdageeks family and I would like to explain the subject in a simplistic way. Let's connect through LinkedIn-

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