Читать книгу Materials for Biomedical Engineering - Mohamed N. Rahaman - Страница 70

A key feature of the amide bond is that the carbonyl (C=O) double bond resonates between the C–O and C–N positions, which gives the C–N bond partial double bond character (Figure 2.19a). The N atom has trigonal planar geometry, in a manner similar to carbon atoms in the ethylene molecule due to sp² hybridized electron orbitals (Section 2.4.2). Because rotation about a double bond is restricted, the amide bond has a planar geometry (Figure 2.19b). This has important consequences for the secondary and tertiary structure of the protein molecule.

Figure 2.19 Schematic illustration of the stereochemistry of the amide bond. (a) Resonance of the carbonyl (C=O) double bond, resulting in partial double bond character of the amine (N–H) bond. (b) Planar geometry of amide bond.