Practice question

In α-helix, peptide bonds are regularly oriented, allowing exciton splitting of strong pi to pi-star transition into parallel and perpendicular components, generating negative bands near 208 nanometers and 222 nanometers from n to pi-star transition, plus positive intense band near 192 nanometers. Intensity at 222 nanometers correlates with helical content. β-sheet shows weaker broad minimum near 215-218 nanometers, random coil shows minimum near 195 nanometers. Observing double minima near 208 and 222 nanometers is definitive fingerprint of significant α-helical secondary structure.