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$-CO-NH-$ (peptide bond): which statement is incorrect about peptide bond : -
A
C–N bond length in proteins is longer than usual bond length of C–N bond
B
Spectroscopic analysis shows planar structure of the $-CO-NH-$ group
C
C–N bond length in proteins is smaller than usual bond length of C–N bond
D
None of above
Detailed Solution
In the peptide group, the lone pair on nitrogen is delocalised into the carbonyl group (resonance): $-C(=O)-NH- \leftrightarrow -C(-O^-)=NH^+-$.
So the C–N bond has partial double bond character. Its length (about 1.32 Å) is shorter than a normal C–N single bond (about 1.47 Å).
Because of this partial double bond, rotation about C–N is restricted and the $-CO-NH-$ group is planar, as shown by spectroscopy and X-ray studies.
So the statement that the C–N bond length in proteins is longer than the usual C–N bond length is incorrect.
So the C–N bond has partial double bond character. Its length (about 1.32 Å) is shorter than a normal C–N single bond (about 1.47 Å).
Because of this partial double bond, rotation about C–N is restricted and the $-CO-NH-$ group is planar, as shown by spectroscopy and X-ray studies.
So the statement that the C–N bond length in proteins is longer than the usual C–N bond length is incorrect.