Vitamin D, example and challenge.
D000475:Alkenes; D055598:Chemical Phenomena; D002621:Chemistry; D004875:Ergosterol; D007536:Isomerism; D008968:Molecular Conformation; D010777:Photochemistry; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D014807:Vitamin D; D014961:X-Ray Diffraction
D000475:Alkenes; D014807:Vitamin D; D004875:Ergosterol