Alpha-helix are formed by an array of consecutive residues with backbone torsion angles around the standard values (fi=-57 and psi=-47). Characteristic NMR restraints are:

Presence of a pattern of consecutive, medium-to-strong d_NN(i,i+1) NOE connectivites accompanied by numerous d_ab(i,i+3), d_aN(i,i+3), and d_aN(i,i+4) interactions.

d_NN(i,i+2) may also be observed, and d_bN(i,i+1) NOEs are usually stronger than in beta-sheets or in random conformations.

String of consecutive small ³J_HN-HA coupling constants (5-6 Hz).

All amide protons (except at the N-terminus) participate in CO(i)/NH(i+4) hydrogen bonds, which results in decreased H/D exchange.

Upfield conformational chemical shift effect of HA (average de -0.39 ppm) and NH (average de -0.19 ppm) protons and downfield effect for CA carbons (average of +2.6 ppm).

¹J_CA-HA of 146.5+-1.8 Hz