Primary structure z The oxygen and hydrogen of the CO-NH group are in the trans position as consequence of the stabilization resonance z α-carbon atoms are the only ones that may rotate freely z -NH- group does not protonate z Polypetidic chain may be presented by a series of rigid planes separated by HCR- groupsPrimary structure z The oxygen and hydrogen of the CO-NH group are in the trans position as consequence of the stabilization resonance z α-carbon atoms are the only ones that may rotate freely z -NH- group does not protonate z Polypetidic chain may be presented by a series of rigid planes separated by HCR- groups