The structure of the α helix. (a) Peptide bonds form a right-handed spiral; intrachain hydrogen bonds are shown. The electric dipole of the helix, established through intrachain hydrogen bonds, propagates to the amino and carbonyl constituents of each peptide bond. The partial charges of the electric dipole are indicated by δ+ and δ−. (b) An easy way to distinguish left- and right-handed helices (see text).