Which statement is incorrect about peptide bond `-oversetOoverset(||)C-ddot(N)H-` ?

Options

A. C-N bond length in proteins is longer than usual bond length of C-N bond
B. Spectroscopic analysis show planar structre of `-underset(O)underset(||)(C)-NH`-group
C. C-N bond length in protiens is smaller than usual bond length of C-N bond
D. None of the above

Explanation

To determine which statement is incorrect about the peptide bond, we need to analyze the properties of the peptide bond and the statements provided.

### Step-by-Step Solution:

1. **Understanding Peptide Bond**: A peptide bond is formed when two amino acids link together through a condensation reaction, resulting in the release of a water molecule. The structure of the peptide bond can be represented as `C(=O)-N`.

2. **Analyzing the Statements**:
- **Statement A**: "C-N bond length in protein is longer than usual bond length of C-N bond."
- **Statement B**: "Spectroscopic analysis shows planar structure of C=O-NH that is peptide group."
- **Statement C**: "C-N bond length in protein is smaller than usual bond length of C-N bond."
- **Statement D**: "None of the above."

3. **Evaluating Statement A**: This statement claims that the C-N bond length in proteins is longer than the usual C-N bond length. However, due to the partial double bond character of the peptide bond (due to resonance), the C-N bond in a peptide is actually shorter than a typical C-N bond. Thus, this statement is incorrect.

4. **Evaluating Statement B**: The planar structure of the peptide bond is well-established in chemistry. The resonance between the carbonyl (C=O) and the amine (N-H) contributes to the planarity of the peptide bond. This statement is correct.

5. **Evaluating Statement C**: This statement correctly states that the C-N bond length in proteins is smaller than the usual C-N bond length due to the partial double bond character. This statement is correct.

6. **Evaluating Statement D**: Since we have identified Statement A as incorrect, this statement is also incorrect.

### Conclusion:
The incorrect statement about the peptide bond is **Statement A**: "C-N bond length in protein is longer than usual bond length of C-N bond."