1. Early studies on the peptide(protein) structure 1.1 The peptide(o=c-n-h) bond was found to be shorter than the c-n bond in a simple amine and atoms attached are coplanar 1.1.1 This was revealed by X-ray diffraction studies of amino acids and of simple dipeptides and tripeptides. 1.1.2 The peptide(amide) bond was c-N double bond, 1.27) thus having partiar'< found to be about 1. A(C-N single bond, 1.49; double bond feature(should be rigid and unable to rotate freely).1. Early studies on the peptide (protein) structure 1.1 The peptide (O=C-N-H) bond was found to be shorter than the C-N bond in a simple amine and atoms attached are coplanar. 1.1.1 This was revealed by X-ray diffraction studies of amino acids and of simple dipeptides and tripeptides. 1.1.2 The peptide (amide) bond was found to be about 1.32 Å (C-N single bond, 1.49; C=N double bond, 1.27), thus having partial double bond feature (should be rigid and unable to rotate freely)