Question

Which statements are correct about peptide bond? (1) \(-\) CONH- group is planar (2) C-N bond length in protein is longer than usual bond length of C-N bond (3) C-N bond length in protein is smaller than usual bond length of C-N bond (a) 2 and 3 (b) 1 and 2 (c) 2 only (d) 1 and 3

Short answer

The correct answer is (d) 1 and 3.

Step-by-step solution

Understanding Peptide Bond Planarity

A peptide bond is a chemical bond formed between two amino acids. It has a planar structure due to resonance, which leads to a partial double bond character in the C-N bond. This planar nature makes statement (1) correct.

Analyzing C-N Bond Length in Peptide Bond

The partial double bond character in the peptide bond causes the C-N bond length to be shorter than a typical C-N single bond, due to increased bond strength. Therefore, statement (3) is correct.

Evaluating Incorrect Statements

Statement (2) is incorrect because it states that the C-N bond length in a peptide bond is longer, whereas due to partial double bond character, it is actually shorter.

Identifying Correct Statements

Based on the analysis, the correct statements are (1) and (3). Therefore, the correct answer is option (d) 1 and 3.

Key concepts

Planar Structure

Did you know that peptide bonds have a unique feature known as planarity? When two amino acids join to form a peptide bond, a special structure emerges. This bond, designated as the CONH group, exhibits a flat or planar structure. But why is that? 👀

The reason behind this planarity is the resonance present in peptide bonds. The chemical nature of this bond includes a blend of a single and a partial double bond. Due to the resonance, electrons are delocalized over the oxygen, carbon, and nitrogen atoms, leading to a fixed, planar geometry.

Imagine a sheet of paper - flat and spread out. That's how the peptide bond behaves, making sure it maintains its planarity. This property is crucial for the overall folding and structure of proteins, as it imparts a certain rigidity to the protein backbone. This rigidity helps proteins maintain their shapes, which is essential for their function in living organisms.

Resonance in Peptide Bonds

Resonance is a fascinating concept in chemistry, especially when it plays a role in peptide bonds. Let's dive into how resonance is responsible for the properties of peptide bonds:

• Resonance involves the overlapping of electron orbitals in adjacent atoms.
• This overlap leads to a stable configuration, distributing electron density across the bond.
• For peptide bonds, the resonance causes partial double bond characteristics between carbon and nitrogen atoms.

What does this mean for the peptide bond itself? Well, the resonance gives the bond an added strength and stability, much stronger than a standard single bond. Additionally, this partial double bond character significantly contributes to the peptide bond's reduced length compared to a regular C-N single bond. Think of it like tightly holding a rope – the bond is stiffer and more compact due to the increased electron sharing. This property of resonance is key in understanding why peptide bonds are shorter than one would expect from a standard C-N single bond.

C-N Bond Length in Proteins

The length of the C-N bond in peptide bonds might seem like a small detail, but it's critical for protein function and structure. Their unique bond length tells us a lot about what's happening at the molecular level.

In peptide bonds within proteins, the C-N bond length is shorter than that of a typical single C-N bond. This is an outcome of the resonance effect which gives the bond partial double bond characteristics. Let’s unravel why this happens:

• The typical C-N single bond length is approximately 1.47 Å (angstrom), while in peptides, due to resonance, it's about 1.32 Å.
• The shorter bond length implies a stronger, more stable bond. The electron sharing between carbon and nitrogen due to resonance creates this effect.
• This shortening and strengthening are crucial for the protein’s structural integrity and its ability to assume functional, complex shapes necessary for biological processes.

The shortened bond length due to partial double bond character equips proteins with the necessary rigidity for proper biological functioning. In essence, if peptide bonds had longer C-N bonds like typical single bonds, proteins might not fold properly, leading to malfunction in biological systems. This subtle change in bond length is fundamental to life as we know it!